current trip meaning

LV switchgear: functions and selection

• LV switchgear functions - Electrical protection
• LV switchgear functions - Isolation
• LV switchgear functions - Switchgear control
• Elementary switching devices
• Combined switchgear elements
• Switchgear selection
• Tabulated functional capabilities of LV switchgear
• Standards and description of circuit-breakers

Fundamental characteristics of a circuit-breaker

• Other characteristics of a circuit-breaker
• Selection of a circuit-breaker
• Coordination between circuit-breakers
• Selectivity MV/LV in a consumer’s substation
• Selectivity of Residual Current Devices (RCDs)
• Maintenance of low voltage switchgear
• 1 Rated operational voltage (Ue)
• 2 Rated current (In)
• 3 Frame-size rating
• 4 Overload relay trip-current setting (Irth or Ir)
• 5 Short-circuit relay trip-current setting (Im)
• 6 Circuit breaker suitable for isolation
• 7 Rated short-circuit breaking capacity (Icu or Icn)
• 9 Related technical guides

The fundamental characteristics of a circuit-breaker are:

• Its rated voltage Ue
• Its rated current In
• Its tripping-current-level adjustment ranges for overload protection (Ir [1] or Irth [1] ) and for short-circuit protection (Im) [1]
• Its short-circuit current breaking rating (Icu for industrial CBs; Icn for domestic-type CBs).

Rated operational voltage (Ue)

This is the voltage at which the circuit-breaker has been designed to operate, in normal (undisturbed) conditions.

Other values of voltage are also assigned to the circuit-breaker, corresponding to disturbed conditions as noted in Other characteristics of a circuit-breaker .

Rated current (In)

This is the maximum value of current that a circuit-breaker, fitted with a specified overcurrent tripping relay, can carry indefinitely at an ambient temperature stated by the manufacturer, without exceeding the specified temperature limits of the current carrying parts.

A circuit-breaker rated at In = 125 A for an ambient temperature of 40°C will be equipped with a suitably calibrated overcurrent tripping relay (set at 125 A). The same circuit-breaker can be used at higher values of ambient temperature however, if suitably “derated”. Thus, the circuit-breaker in an ambient temperature of 50°C could carry only 117 A indefinitely, or again, only 109 A at 60°C, while complying with the specified temperature limit.

Derating a circuit-breaker is achieved therefore, by reducing the trip-current setting of its overload relay, and marking the CB accordingly. The use of an electronic-type of tripping unit, designed to withstand high temperatures, allows circuit-breakers (derated as described) to operate at 60°C (or even at 70°C) ambient.

Note: In for circuit-breakers (in IEC 60947-2) is equal to Iu for switchgear generally, Iu being the rated uninterrupted current.

Frame-size rating

A circuit breaker which can be fitted with overcurrent tripping units of different current level-setting ranges, is assigned a rating which corresponds to the highest current-level-setting tripping unit that can be fitted.

A Compact NSX630N circuit-breaker can be equipped with 11 electronic trip units from 150 A to 630 A. The size of the circuit-breaker is 630A.

Overload relay trip-current setting (Irth or Ir)

Apart from small circuit-breakers which are very easily replaced, industrial circuit-breakers are equipped with removable, i.e. exchangeable, overcurrent-trip relays. Moreover, in order to adapt a circuit-breaker to the requirements of the circuit it controls, and to avoid the need to install over-sized cables, the trip relays are generally adjustable. The trip-current setting Ir or Irth (both designations are in common use) is the current above which the circuit-breaker will trip. It also represents the maximum current that the circuit-breaker can carry without tripping. That value must be greater than the maximum load current IB, but less than the maximum current permitted in the circuit Iz (see chapter Sizing and protection of conductors ).

The thermal-trip relays are generally adjustable from 0.7 to 1.0 times In, but when electronic devices are used for this duty, the adjustment range is greater; typically 0.4 to 1 times In.

(see Fig. H27 )

A NSX630N circuit-breaker equipped with a 400 A Micrologic 6.3E overcurrent trip relay, set at 0.9, will have a trip-current setting:

Ir = 400 x 0.9 = 360 A

Note: For circuit-breakers equipped with non-adjustable overcurrent-trip relays, Ir = In. Example: for iC60N 20 A circuit-breaker,

Ir = In = 20 A.

Short-circuit relay trip-current setting (Im)

Short-circuit tripping relays (instantaneous or slightly time-delayed) are intended to trip the circuit-breaker rapidly on the occurrence of high values of fault current. Their tripping threshold Im is:

• Either fixed by standards for domestic type CBs, e.g. IEC 60898, or,
• Indicated by the manufacturer for industrial type CBs according to related standards, notably IEC 60947-2.

For the latter circuit-breakers there exists a wide variety of tripping devices which allow a user to adapt the protective performance of the circuit-breaker to the particular requirements of a load (see Fig. H28 , Fig. H29 and Fig. H30 ).

• ^ 50 In in IEC 60898, which is considered to be unrealistically high by most European manufacturers (Schneider Electric = 10 to 14 In).
• ^ 1 2 For industrial use, IEC standards do not specify values. The above values are given only as being those in common use.

Circuit breaker suitable for isolation

A circuit-breaker is suitable for isolating a circuit if it fulfills all the conditions prescribed for a disconnector (at its rated voltage) in the relevant standard. In such a case it is referred to as a circuit-breaker-disconnector and marked on its front face with the symbol

All Acti 9, Compact NSX and Masterpact LV switchgear of Schneider Electric ranges are in this category.

Rated short-circuit breaking capacity (Icu or Icn)

The short-circuit current-breaking performance of a LV circuit-breaker is related (approximately) to the cos φ of the fault-current loop. Standard values for this relationship have been established in some standards

The short-circuit current-breaking rating of a CB is the highest (prospective) value of current that the CB is capable of breaking without being damaged. The value of current quoted in the standards is the rms value of the AC component of the fault current, i.e. the DC transient component (which is always present in the worst possible case of short-circuit) is assumed to be zero for calculating the standardized value. This rated value (Icu) for industrial CBs and (Icn) for domestic-type CBs is normally given in kA rms.

Icu (rated ultimate s.c. breaking capacity) and Ics (rated service s.c. breaking capacity) are defined in IEC 60947-2 together with a table relating Ics with Icu for different categories of utilization A (instantaneous tripping) and B (time-delayed tripping) as discussed in Other characteristics of a circuit-breaker .

Tests for proving the rated s.c. breaking capacities of CBs are governed by standards, and include:

• Operating sequences, comprising a succession of operations, i.e. closing and opening on short-circuit
• Current and voltage phase displacement. When the current is in phase with the supply voltage (cosφ for the circuit = 1), interruption of the current is easier than that at any other power factor. Breaking a current at low lagging values of cosφ is considerably more difficult to achieve; a zero power-factor circuit being (theoretically) the most onerous case.

In practice, all power-system short-circuit fault currents are (more or less) at lagging power factors, and standards are based on values commonly considered to be representative of the majority of power systems. In general, the greater the level of fault current (at a given voltage), the lower the power factor of the fault-current loop, for example, close to generators or large transformers.

Figure H31 below extracted from IEC 60947-2 relates standardized values of cos φ to industrial circuit-breakers according to their rated Icu.

• The dielectric withstand capability
• The disconnection (isolation) performance and
• The correct operation of the overload protection have not been impaired by the test.
• ^ 1 2 3 Current-level setting values which refer to the current-operated thermal and “instantaneous” magnetic tripping devices for over-load and short-circuit protection.

Related technical guides

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What Does a Circuit Breaker Tripping Mean?

 when there's a circuit breaker tripping, it can indicate that the circuit breaker detects an electrical issue, and it shouldn't be ignored..

The pandemic-induced surge in home electricity use is real. Consider that, according to the National Bureau of Economic Research, American spending on  home power consump tion  skyrocketed by $6 billion! 

With more usage comes more problems, and circuit breaker issues are among the most common. When there's a circuit breaker tripping, it can indicate that the circuit breaker detects an electrical issue, and it shouldn't be ignored.

 Circuit Breaker Tripping 101

Most circuit breaker issues center around circuit overload. Circuit breakers are a vital part of your home's electrical system since they are designed to prevent costly and damaging surges in electrical current. 

The breaker, working in tandem with a fuse, serves as an electrical unit's internal sensing mechanism. At the slightest sense of excess current, the circuit breaker will "trip," triggering a cease in all electrical activity within the circuit.

Not only can such a smart mechanism help with preventing damage to wires and other electrical components, but circuit breakers can also save lives by preventing electrical fires. According to the National Fire Protection Association,  electrical failures  were the second leading cause of home fires between 2012-2016.

So why do circuit breakers trip? Here are the three most common reasons for circuit breaker tripping and how you can go about fixing a circuit breaker.

 1) Circuit Overload

By far, the m ost common reason a circuit trips is because it's overloaded. Even running a circuit at its electrical capacity can cause home appliances to burn out or a circuit to trip. Ideally, you want to run a circuit below its capacity to keep it from tripping and to prevent any damage from occurring. 

The most familiar example of circuit overload is an over-stuffed power outlet. When you have a dozen gadgets all demanding electrical current to work, eventually that single outlet's capacity will experience overload, and the circuit will trip.

Knowing what each electrical outlet in your house can handle is key to preventing circuit overload. Even a single high-current appliance like a washing machine cannot plug into just any outlet.  Understanding your power outlets  is critical for a safer home.

Before you head to your circuit breaker box or call your electrician, notice what was plugged in at the outlet where the tripped circuit occurred. You may have overloaded it.

 2) Short Circuit

Similar to an overload, when a circuit "shorts," it responds to more current than it can bear. But a short circuit is far more dangerous. 

A short circuit occurs when a "hot" or active wire comes into contact with either another active wire or a neutral wire. The touching wires cause a spike in current that can likewise trip your circuit breaker. Most often, the causes for short circuits are mechanical issues like: 

• Loose Connections
• Improper Wiring
• Damaged Wires

Faulty components, like switches, plugs, cords, appliances, or lighting fixtures, are often culprits of short circuits. Short circuits can occur if you screw or nail into drywall and penetrate an electrical wire.

Remember that short circuits may involve faulty circuit wiring, but the device you're plugging in can cause the problem as well. Keep this in mind, especially if you're using older devices or gadgets that have been out of commission for years, as these can be more prone to short circuits, independent of what's going on in the outlet.

Due to their volatile nature, short circuits are some of the biggest causes of electrical fires, so be extra attentive and don't hesitate to call a professional. As a general rule, most people should never  DIY electrical issues  in their homes.

 3) Ground Fault Surge

 Ground fault surges are similar to short circuits because they involve a sudden spike in current, creating an overload. Ground faults occur when an active wire comes into contact with the ground wire. The contact can come directly or indirectly via the metal housing that connects to the ground wire. 

Copper grounding wires are especially prone to ground fault surges. Copper is the most  conductive material  in everyday use when it comes to home electrical systems. When a hot wire touches the ground wire's copper coating, it results in superconductivity that overwhelms the circuit. A similar result can come from an active wire touching a ground's metal outlet box. 

 Understanding and Fixing Circuit Breaker Issues

So how should you go about troubleshooting a circuit breaker issue? Even though you should leave anything remotely technical to a professional, there are a few things you can do to investigate circuit breaker trip meaning.

First thing's first. Make sure you and your family are safe. Check for signs of excess heat or burning—smell for what could be smoke from an electrical fire. If you sense any signs of a fire, evacuate and call 911.

Check for any discoloration around an outlet. Also, make a note of any sparks or popping noises coming from the outlet. Any of these could be a sign of a ground fault surge or a short, in which case simply flipping the circuit breaker switch won't help. And remember, the older the outlet, the more likely it is to experience problems.

Look for any signs of damage to your devices. Remember that the problem could be coming, not from your home's outlet, but from what you plugged in.

If there are no signs of a blown circuit, try going to your circuit breaker service panel. You may be familiar with this metal box, often located in a garage or utility room. Flip the switch of the house area that tripped, and see if that "resets" the circuit. 

 Fixing a Circuit Breaker

If a simple flipping of the switch doesn't work, it's time to call a professional electrician. The seasoned team at Buell Electric can assess the problem and fix a circuit breaker, which may involve repairs or upgrades. 

Circuit breaker tripping may be as innocent as overloading an outlet, but it can point to more serious problems as well. The best way to know for sure is to  contact us  today.

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What Causes Circuit Breakers To Trip?

• May 2, 2024

Should your circuit breakers frequently trip, there’s no cause for alarm. It’s quite a common occurrence. Below are explanations for why this happens and advice on how to prevent it in the future. Master your circuit breaker problems!

Table of Contents

Understanding Circuit Breaker Tripping

Circuit breakers are protection devices for electrical circuits. When too much current passes, the breaker trips, stopping the flow of electricity and preventing damage. This can be caused by faulty wiring, too many appliances on one circuit, or a ground fault.

Overloading can cause tripping. This happens when too many devices are connected to a single circuit. Heat builds up in the wires, which can start fires or cause damage. To prevent this, distribute loads across multiple circuits and don’t connect too many appliances to one outlet.

Short circuits also lead to tripping. This happens when two wires with opposite charges come in contact or when a wire touches something grounded. This causes an immediate surge in current that triggers the breaker. Check for exposed wires or insulation damage, and call an electrician if you spot any signs of trouble.

Ground faults can also cause tripping. This happens when there’s an unintentional connection between a live wire and a conductive surface. Install GFCIs to avoid this.

In short, know what causes circuit breakers to trip. Identify potential hazards like overloading, short circuits, and ground faults. Take steps to prevent accidents and ensure your electrical equipment is safe. If you’re unsure how to handle electrical problems, call a licensed electrician.

Overloading Causes

Circuit breakers trip to stop overheating, electrical fires, and damage to electrical parts. Plugging in too many devices can cause the circuit to become overloaded, so the breaker trips to cut off the power.

Short circuits are like a blind date gone wrong. They can be explosive, and often end in disaster. This happens when a hot wire comes into contact with a neutral or insulation/water. This throws off the electric balance, causing danger and tripping.

Short Circuit Causes

A short circuit happens when a low-resistance path appears between two points in the circuit that aren’t usually connected. This can cause too much current to flow, making a circuit breaker trip. Insulation or wiring damage, faulty appliances, and circuit overload are the most common reasons for a short circuit. It’s critical to identify and fix the root cause quickly to avoid electrical fires and other dangers .

When too much power passes through a circuit, the circuit breaker will automatically turn off. It’s designed to protect wiring and guard against electrical accidents . But if the breaker trips regularly, there may be underlying issues that need investigation and repair. Often times, this means upgrading or replacing components.

Sometimes short circuits are caused by human error or wear and tear. But they may also come from design or installation problems. Planning and upkeep from local electricians can keep electrical systems running safely and appropriately for a long time. If your circuit breaker is tripping a lot, get an experienced technician to review your system and suggest solutions that match your needs and budget .

Overheating Causes

Circuit breakers are essential safety features. They stop electrical fires and protect your appliances. When overloaded, too much current flows, producing heat. This causes the breaker to trip!

Other factors can cause overheating. Damaged insulation on wires increases resistance. Loose connections add resistance and heat. High temperatures and poor ventilation worsen the situation.

It’s important to maintain and service the electrical system. Checks of all components will make sure they work efficiently. To avoid tripping, prevent overheating. This will reduce energy consumption and safeguard equipment. So, let’s learn about circuit breakers and how they deal with overloads!

Circuit Breaker Types

Circuit breakers are essential for any electrical system. They prevent overloaded and faulted circuits . There are different types of circuit breakers suitable for specific electrical loads.

See the table below for the different types of circuit breakers and their functions:

It is crucial to select the right type of breaker. Each one has its own advantages in specific situations. For instance, thermal circuit breakers are perfect for small appliances like hair dryers or irons . Meanwhile, magnetic circuit breakers are great for bigger loads such as air conditioners or refrigerators .

Remember, circuit breakers are like Beyoncé – they can handle a lot, but have their limits.

Circuit Breaker Ratings and Specifications

Circuit breakers are designed to protect electrical circuits from overloads. To ensure that circuits and appliances are safe, the ratings and specifications of circuit breakers need to be understood.

If a circuit breaker trips often, it may mean there’s an issue. It’s best to get professional help in these cases. Time to go on a hunt for your electrical wiring!

Troubleshooting Circuit Breaker Tripping

Circuit breakers can flip out for multiple reasons, like overloads , short circuits , and ground faults .

Overloads happen when too much electricity passes through the circuit, creating too much heat and tripping the breaker. Short circuits are when two or more wires touch, resulting in extra current. Ground faults occur when the power takes an unexpected route, like through a person’s body.

To figure out why your circuit breaker is tripping, it’s important to figure out what is going on and act accordingly. Inspections and maintenance can also help avoid future tripping.

Stop your circuit breaker from misbehaving with these prevention tips!

Preventing Circuit Breaker Tripping

A circuit breaker tripping can be prevented with understanding. When circuits are overloaded, breakers trip to avoid overheating and potential fires. Here are 3 steps that can help you prevent circuit breakers tripping:

• Know the electrical load – work out how many appliances & devices are connected to one circuit. Don’t overload them by spreading high-energy equipment across multiple circuits .
• Look after your appliances – ensure all your appliances & devices are in good condition, with no damaged cords or frayed wires.
• Upgrade your system – if you’re tripping breakers often you may need to upgrade the electrical system with higher capacity breakers or more circuits.

Plus, investing in surge protectors can also assist in preventing circuit overload and subsequent tripping of breakers. By following these steps you can make sure your home’s electricity runs safely and without interruption due to circuit breakers tripping.

Remember: these precautions will keep you from tripping more than just your circuit breakers!

Safety Precautions

Safety must be taken seriously when dealing with circuit breakers . Always switch off the main power supply before beginning work. Wear protective gear such as insulated gloves and boots to stay safe from electrocution. Never touch wires or components inside the box without proper training. Keep the area around the breaker box free from any flammable substances. Inspect breakers for damage or wear regularly .

Label each circuit breaker correctly . Test them frequently for functionality. This will help identify circuits quickly in case of an emergency. These precautions and practices ensure safety while dealing with circuit breakers. When in doubt, blame it on the circuit breaker – it’s always a good scapegoat for electrical woes!

Circuit breakers are essential components of any electrical system. They stop too much current flowing and thus, protect against potential fires . The most common cause for tripping is overload. But, other causes like short circuits and ground faults can also cause the breaker to trip. When it trips, there is something wrong that needs to be fixed right away.

Short circuits occur when two wires touch each other. This creates a low resistance path which allows a lot of current to flow with no load. Ground faults occur when the hot wire touches something incorrectly wired or with a damaged cord.

To prevent tripping, regular maintenance of the electrical system is needed. Keeping appliances in good condition, replacing worn-out cords and fixtures, and periodically checking for loose wires all help reduce the chances of tripping. In summary, understanding why the breaker trips and taking precautionary measures will keep you safe and save you repair costs.

Frequently Asked Questions

1. what causes a circuit breaker to trip.

There are several possible causes, including overheating due to circuit overload, short circuits, ground faults, and age-related wear and tear.

2. How can I prevent my circuit breaker from tripping?

You can avoid overloading your circuit by keeping the number of electrical appliances used on one circuit to a minimum, regularly checking wires for signs of wear and tear, and not using too many extension cords.

3. What should I do if my circuit breaker keeps tripping?

If your circuit breaker is constantly tripping, it is important to identify and fix the underlying issue. Contact an electrician to inspect and repair any faulty wiring or electrical devices.

4. Can a circuit breaker trip without an overload?

Yes, a circuit breaker can trip due to a short circuit or a ground fault, which may occur without an overload.

5. How do I reset a tripped circuit breaker?

To reset a tripped circuit breaker, turn it off and then back on again. Make sure to identify and correct the underlying issue that caused the trip before restoring power.

6. What is the lifespan of a circuit breaker?

The lifespan of a circuit breaker can vary depending on usage and other factors. However, most circuit breakers last between 10 and 30 years.

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• How to Prevent Circuit Breaker from Tripping
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Home > Protection > Tripping Curves of Circuit Breakers – B, C, D, K and Z Trip Curve

Tripping Curves of Circuit Breakers – B, C, D, K and Z Trip Curve

Types of circuit breaker based on its tripping curve.

A circuit breaker is a protection device employed in every electrical circuit to prevent any potential hazard. There are different types of circuit breakers used all over the world due to their various characteristics & applications. It is necessary to have a circuit breaker that offers adequate protection so that one can work safely around it without having fear of any potential hazards. That is why it is best to know about these kinds of circuit breakers & what kinds of protection do they offer before buying one.

Table of Contents

What is a Circuit Breaker?

A circuit breaker is an electrical device that provides protection against fault current. It breaks the circuit in case of overloading & short circuit. The fault currents generated due to these fault conditions can damage the electrical devices as well as cause fire in a building that can also pose danger to human life.

The circuit breaker instantly cut off the power supply to reduce further damage. A circuit breaker has two types of tripping unit i.e. thermal and magnetic tripping unit.

Thermal Tripping Unit: the thermal tripping unit is used for protection against overloading. It uses a bi-metallic contact that bends with a change in temperature. The current flowing through the bimetallic strip heats up contact & trip the circuit breaker.

The rate of bending of the bi-metallic strip depends on the amount of current. Therefore, greater the overloading current, faster the circuit breaker trips.  

Magnetic Tripping Unit: The magnetic trip unit is used for protection against short circuit current. it includes a solenoid that produced a strong magnetic field due to high short circuit current to instantly trip the circuit breaker.

Related Posts:

• MCB (Miniature Circuit Breaker) – Construction, Working, Types & Applications
• MCCB (Molded Case Circuit Breaker) – Construction, Types & Working

What is a Trip Curve?

A trip curve also known as a current time graph is a graphical representation of the response of a circuit breaker. It shows the current relationship with the tripping time of a protection device.

Why We Need Different Tripping Curves?

Circuit breakers are used for tripping the power supply as quickly as possible in case of overcurrent. But it should not trip so fast & unnecessary that it becomes a problem.

The overcurrent can happen under normal conditions such as the inrush current of a motor. Inrush current is the huge current draw during the starting of a motor that causes voltage dips in the main line. The circuit breaker should be able to tolerate the inrush current & it should provide some delay before tripping.

Therefore, the circuit breaker selected should not trip so fast that it creates a nuisance & it should not trip so late that it causes any damage. This is where the tripping characteristics of the circuit breakers come into play.

The tripping curve tells how fast a circuit breaker will trip at a specific current. The different tripping curves classify the circuit breakers into categories where each category is used for specific types of loads. It is essential to select a circuit breaker that provides the necessary overcurrent protection.

• Types of Circuit Breakers – Working and Applications
• Air Circuit Breaker (ACB): Construction, Operation, Types and Uses

How to read a Trip Curve?

The following figure shows a chart of a trip curve.

The horizontal X-axis represents the multiples of the current flowing through the circuit breaker. While the Y-axis represents the tripping time of the circuit breaker on a logarithmic scale.

The thermal region shows the response of the bimetallic contact trip unit during overcurrent. The curve shows that the circuit breaker’s tripping time reduces with an increase in the current. The first curve in the graph shows the response of a thermal trip unit.

While the magnetic region shows the response of the solenoid to fault current such as a short circuit current.

As seen from the graph, a circuit breaker does not have a fixed tripping time and we cannot predict an exact tripping point. It is because the tripping is affected by ambient conditions such as temperature. Think of it as a Schrödinger’s Cat area, we do not know when the tripping will occur unless the event happens. 

Types of Circuit Breaker Based on Tripping Curves

The circuit breakers are classified into the following five types based on their tripping curves.

Such type of circuit breaker is designed to instantly trip when the operating current is 3 to 5 times its rated current. Their tripping time falls between 0.04 to 13 seconds. They are suitable for domestic applications where surges are very low such as lighting & resistive loads.

They are sensitive and must not be used in places where the normal surges keep on tripping it unnecessarily.

Type C circuit breaker trips instantly at current surges 5 to 10 times its rated current. its tripping time lies between 0.04 to 5 seconds. As they can tolerate higher surge currents, they are used in commercial applications such as the protection of small motors, transformers, etc.

Type D circuit breaker trips instantly when operating current reaches 10 to 20 times its rated current. Its tripping time is 0.04 to 3 seconds. Such circuit breakers can tolerate the high inrush current of large motors. Therefore, they are suitable for running heavy loads in industrial applications.

Such type of circuit breakers trips at 10 to 12 times its rated current with a tripping time of 0.04 to 5 seconds. These circuit breakers are also used for heavy inductive loads in industrial applications.

Type Z circuit breakers are the most sensitive circuit breaker that instantly trips when the operating current reaches 2 to 3 times its rated current. They are used for sensitive equipment that requires very low short circuit trip settings. 

• Main Difference between Fuse and Circuit Breaker
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• How to Read MCB Nameplate Data printed on it?
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• Why Circuit Breaker Capacity Was Rated in MVA and Now in kA and kV?
• How to Wire 120V and 240V Main Panel? Breaker Box Installation – US – NEC
• How to Wire Single-Phase, 230V Consumer Unit (Breaker Box) with RCD? IEC, UK and EU

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Do we have to consider the tripping curves for DIY installation?

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MCCB Current Setting | I2t | Ir | Isd | Ii | Ig Explanation

Mccb current setting:.

MCCB is nothing but a molded case circuit breaker. It is designed to operate all indoor application. MCCB contains the following protection such as over current, short circuit, Instantaneous and earth fault. During loading condition all the protection will be enabled automatically. The current reference will be come from the phase current transformer, which will be placed inside of the MCCB. However, in this article we are going to see the MCCB current setting and how to set MCCB.

MCCB Current Rating:

Refer the picture of a 800 A MCCB trip Unit. In that, I n notates the nominal per phase current of the MCCB. Also, in this type of current setting, you cannot set the over current limit for each phase of the MCCB. Once You set in that, it considers all three phase. Lets see….the common current setting value.

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Over current Protection (Ir):

It is denoted By Ir. Here sub-ordinate r mentions that rated current. This the first dial. It starts from 0.4 to 1.0 which means 40% to 100% of the Nominal current. Typically,

In Our case we have set the MCCB to operate the over current at 320Amps. Also, these type of over current protection are said to be a definite time protection.

Note: For circuit-breakers equipped with non-adjustable overcurrent-trip relays, Ir = In

Over current protection time setting (tr):

It is denoted by tr. In this dial, we set the time limit for the over current protection as we said above. In our case we have set 0.5 sec. It means, the MCCB allows 320+ Amps for just 0.5 sec only. Beyond that limit MCCB trips the circuit. i.e if you have 319 Amps also, it does not count the time, the MCCB become inoperative.

Also another instruction that you can see, @6 Ir, It means the MCCB has overcurrent of 6 times of the rated set current, then it trips immediately Without time delay even without fault.

Short Circuit Protection (Isd):

Current setting:

Short circuit protection is denoted by (Isd). Sd is s short form of short circuit adjustable protection. In our case you can calculate that, Isd = 1.5 Ir. Here you should consider the over current setting Ir value Not a nominal current value of the MCCB (In). because of when increasing in over current, simultaneously, it increases the short circuit current rating also. In our case Isd= 1.5 * 320 A = 500Amps. The MCCB will trip the circuit when the current increases to 500 Amps with the definite time delay.

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Short Circuit Time Delay (Tsd):

The time delay of short circuit current that MCCB allows to flow beyond that limit MCCB trip the circuit or in simple words, MCCB short circuit current time delay.  In our case, Tsd is 0.1 sec. It means the MCCB allows 500 Amps short circuit current for 0.1 sec.

In this You can see that, the time setting is divided into two-time delay, here white color is called trip setting and black color is called alarm setting. If you accidently set the tsd value in alarm dial means, the MCCB do not trips the circuit under any short circuit fault condition. Instead it gives signal alarm only.

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Also 0 sec means switch-off the protection.

I 2 t Protection (i square t protection)

Another one thing that, you should note that I 2 t Protection.  I 2 t protection means the trip unit consider the equipment temperature. The Value of the I 2 t can be calculated by

I 2 t = k 2 S 2

which shows that the allowable heat generated is proportional to the squared cross-sectional-area of the conductor. where

t = Duration of short-circuit current (seconds)

S = Cross sectional area of insulated conductor (mm2)

I = Short-circuit current (A r.m.s.)

k = Insulated conductor constant (which can be calculate using this )

Instantaneous current setting (Ii):

It is denoted by Ii. Subordinate i means instantaneous. Instantaneous fault means the current goes high in very short period. To protect the circuit against such fault these instantaneous protection is used. In our case Ii = 2 * In => Ii= 2* 800Amps => 1600Amps.

Ii protection does not have time delay, typically it operates at 0 sec when the fault occurs. But in practical case 0 sec is not possible and it takes 30 to 50 ms for relay processing time.

Earth Fault Protection or ground fault protection (Ig):

Any one or more phases contact with the ground conductor; such fault is called Earth fault or ground fault. It is denoted by Ig. In our case, it set in Position A., It means the manufacturer already defined the value of A approx. 100 to 200 Amps. Also the remaining position (B, C, D, …. J ) also mentions the same. Each dial has its own tripping amount of current.

Time setting for ground fault:

It is denoted by Tg. Small g means ground fault. In our case, the time delay is 0.1 sec. The MCCB allows 0.1 sec time delay beyond that limit, the MCCB trips. Remember that, the time setting have two dial as we said in short circuit time relay (alarm and trip).

Thanks You guys we have studied about the MCCB current setting.

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“Also another instruction that you can see, @6 Ir, It means the MCCB has overcurrent of 6 times of the rated set current, then it trips immediately Without time delay even without fault”

Good information on this page but are you sure the above statement is correct ?

The dial would seem to suggest that the delay bands are labelled in seconds of over current at six times the (Ir) rating i.e. in the above example Ir is set to 320A * 6 = 1920A. So overcurrent trip within 0.5 seconds @ 1920A.

Good info, but in: “Also another instruction you can see, @ 6 Ir, it means that the MCCB has an overcurrent of 6 times the rated current set, then it trips immediately without time delay even without faults” is it correct? If it is, the high setting for overcurrent protection would not make sense.

Sir, I would like to thank you from my bottom of heart for your illustrious explanations.

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MCB Trip Curves – B, C, D, K, and Z trip curves

MCB (Miniature circuit breaker) is a re-settable device designed to protect a circuit from short circuits and overcurrents. The trip curve of an MCB (B, C, D, K, and Z curves) tells us about the trip current rating of Miniature Circuit breakers. The trip current rating is the minimum current at which the MCB will trip instantaneously. It is required that the trip current must persist for 0.1s.

Class B trip curve

Class c trip curve, class d trip curve, class k trip curve, class z trip curve, class a trip curve, importance of mcb trip curve types, trip curves for other circuit breakers.

The MCB trip curves, also known as I-t tripping characteristic consist of two sections viz, overload section and short circuit section. Overload section describes the trip time required for various levels of overload currents and the short circuit section describes the instantaneous trip current level of MCB.

Read More: Miniature Circuit Breaker (MCB) – Principle of operation

The MCB with  class B trip characteristics trips instantaneously when the current flowing through it reaches between 3 to 5 times the rated current. These MCBs are suitable for cable protection.

MCB with class C trip characteristics trips instantaneously when the current flowing through it reaches between 5 to 10 times the rated current. Suitable Domestic and residential applications and electromagnetic starting loads with medium starting currents.

MCB with  class D  trip characteristics trips instantaneously when the current flowing through it reaches between Above 10(excluding 10) to 20 times the rated current. Suitable for inductive and motor loads with high starting currents.

MCB with class K trip characteristics trips instantaneously when the current flowing through it reaches between 8 to 12 times the rated current. Suitable for inductive and motor loads with high inrush currents.

MCB with class Z  trip characteristics trips instantaneously when the current flowing through it reaches between 2 to 3 times the rated current. These types of MCBs are highly sensitive to short circuits and are used for the protection of highly sensitive devices such as semiconductor devices.

MCB with class A  trip characteristics trips instantaneously when the current flowing through it reaches between 2 to 3 times the rated current. Like Class Z MCBs, these are also highly sensitive to short circuits and are used for the protection of semiconductor devices.

MCBs with trip curve class B and trip curve class C is the most commonly used ones. MCBs with Class C trip curves can be found in the lighting power distribution boards in residential and commercial buildings. It trips as soon as the current rises between 5 to 10 times its rated current. Class B MCBs are used in the protection of electronic devices such as PLC, DC power supplies, etc. in control panels. It trips as soon as the current rises between 3 to 5 times its rated current.

In some applications, frequent current peaks occur for a very short period (100ms to 2s). For such applications, class Z-type MCBs shall be used. Class Z-type MCBs are used in circuits with semiconductor devices.

It is important to choose an appropriate MCB current rating and trip curve in order to safeguard the circuit from damage during faults. Hence it is necessary to calculate the short circuit current and inrush current before choosing an appropriate MCB rating. If the chosen MCB rating is much higher than required, then it may not trip in the event of a fault. Similarly, if the MCB is underrated, then it may cause nuisance trips, for example even the starting currents or inrush currents may trip the MCB.

External selection tool: https://new.abb.com/low-voltage/solutions/selectivity/tools-support/curves

All circuit breakers, such as MCCB, ACB, VCB, etc have their own trip characteristics. The only thing is that may not follow the categorization as that of MCB. Also, the circuit breaker curve types are not the same for all types of circuit breakers. It varies from one circuit breaker type to the other and depends on many design factors.

Learn more about MCB:

• What is an MCB?
• Miniature Circuit Breaker (MCB) – Principle of operation
• What is kA rating of MCB and MCCB?

Related Articles: 1.  Difference between MCB and MCCB 2.  Difference between contactors and relays 3.  Difference between Soft Starters and VFDs 4.  Difference between MCCB and RCCB 5.  Difference between MCB and RCBO 6.  Difference between RCCB and RCBO 7.  Difference between MPCB and MCCB

27 thoughts on “MCB Trip Curves – B, C, D, K, and Z trip curves”

Very good explanation. I understood the concept. Thank you.

Thank you, Mr. Sanket. Kindly browse through our articles. Please subscribe or follow us on twitter/facebook for instant updates.

Thankhs google team good explace thanks again

Very good mcb make , what Amps load trip make

Very good. Nice explain.. Good job

Explanation is good but your second paragraph doesn’t match the charts. It looks like it is the B-curve that trips between 3-5 times its rated current, and C-curve that trips between 5-10 times its rated current.

Very good, thanks

very good …..thanks

Thanks very much

Very good explanation

Is this curves is applicable to Rccb ?

No. These curves are applicable for mcbs only.

Thanks for your information

The information about mcb is very useful and helpful for a technician, many many thanks for sharing your information.

Great information, I got to know a few more details out of what I wanted to know.

Which type is better choice for UPS protection?

The explanations are very good but in the video is a mistake at minute 0.38. The short circuit sections with the overload section are reversed.

Good for selection of MCB’s

On the c type Mcb on the time curves at a short circuit fault current at 220amp it shows dis connection at 6/7seconds are you saying that disconnection will be instant at this current or 6/7 seconds.

I use B-curve in my home when short circuit occured in the appliace MCB tripped but my appliance burned. My appliance lead wires were shorted by a metal piece was lying on it.I thought MCB could have protected but not. And I also headed big noise of it.

Sorry to hear that. This could be because the MCB was oversized: Much higher than the rated current of the appliance or the MCB could be faulty. We suggest you replace it with a new one. Make sure that you are choosing the right one.

Thanks for sharing such an informative article about MCB.

sir Type C is used for average current load. Type B and C are the most commonly used in DBs. Tripping of MCB Type C is 5-10 times higher than normal.  eg: if a 6A mcb put in acircuit , the rated current is 6 A , then how ever the type c mcb with stand 5 to 10 times higherr than normal .

hello, what about the CL curve mcb, because in my home installation I used the cl4 code on the mcb

Perhaps you are referring to product name of the MCB and not its trip curve.

The information is quite educative. Thank you so much

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Power circuit breaker ratings explained

Darryl Moser Sales Enablement Manager ABB Electrification Products Division

When selecting the right low voltage power circuit breaker for an application, it is important to consider both short-circuit current ratings and short-time current ratings. Understanding these performance characteristics will help you choose between the various circuit breaker designs.

A circuit breaker is selected based on its electrical ratings to serve a particular purpose in each application, proper selection of the circuit breaker is essential for the safe and correct operation of the electrical system. Two important ratings to consider are; short-circuit current rating (this is commonly referred to as the maximum interrupting rating) and the short-time current rating. In this post, we will discuss these circuit breaker ratings and how they can affect the protection and selective coordination of the system.

Short-circuit current ratings defined

The short-circuit current rating is the maximum short circuit current that the circuit breaker is rated to safely interrupt at a specific maximum voltage. This short-circuit current rating is normally expressed in rms symmetrical amperes and is specified by the current magnitude only. If a circuit breaker is provided with instantaneous phase trip elements, the interrupting capacity is the maximum rating of the device with no intentional delay. If the circuit breaker is provided without instantaneous phase trip elements, or if the instantaneous phase trip elements can be disabled by the user, the interrupting capacity is the maximum rating of the device for the rated time interval. An engineer can safely apply a circuit breaker in a power system where the available short-circuit fault current on the supply side terminals does not exceed its maximum interrupting rating.

Short-time current ratings defined

The short-time current rating of a circuit breaker is the ability of the circuit breaker to withstand the effects of the rated short-time current level over defined time duration. It demonstrates the ability of the breaker to remain closed for a time interval under high fault current conditions. The short-time current rating is used by the engineer to determine the ability of the circuit breaker to protect itself and to coordinate with other circuit breakers so the system will trip selectively.

Switchgear ratings

Users of low-voltage switchgear commonly use the phrase “bus bracing” to refer to the mechanical strength of the bus bar system in the equipment, but when you look into the standards you will not find “bus bracing” defined or listed as a rating. The product standards applicable to Metal-Enclosed Power Circuit Breaker Switchgear are IEEE C37.20.10 for definitions and IEEE C37.20.1-2018 and C37.51- 2018 for the ratings; [1] [2] [4].

“Rated short-circuit withstand current: The maximum rms current that a circuit can carry momentarily without electrical, thermal, or mechanical damage or permanent deformation. The current shall be the rms value, including the dc component, at the major peak of the maximum offset phase as determined from the envelope of the current wave during a given test time interval.” [1]

For ratings, reference IEEE C37.20.1 – 2015, IEEE Standard for Metal-Enclosed Low-Voltage (1000 Vac and below, 3200 Vdc and below) Power Circuit Breaker Switchgear. [2]

Rated short-circuit withstand current, which is the rated symmetrical short-circuit current that the switchgear bus must be able to withstand for a time duration of at least four electrical cycles, 0.067 seconds on a 60 Hz system. During this test the voltage must be at the maximum rated value such as 635V as opposed to a nominal value of 600V and it must be at a power factor of 15% or lower which translates into a peak current of at least 2.3 times the rms value.

The test to verify rated short-time withstand current in low-voltage metal enclosed switchgear is conducted by applying the short-time current level for two periods of one-half second (30 cycles), separated by a fifteen second interval with no current; or, at the option of the switchgear manufacturer, the test can be performed as a single test of one full second (60 cycles).

Circuit breaker ratings

The rated short-time current in LVPCBs is a rating given to non-automatic circuit breakers, those without trip units, and for non-fused automatic circuit breakers.

Note: Rated short-time withstand current is not applicable to fused circuit breakers as the fuse will open prematurely and not allow the current to flow for the full duration of the rated short-time withstand test.

Modern electronic trip units allow for maximum time-current curve shaping which helps you to selectively coordinate with other circuit breakers. These trip units are designed with adjustments for long-time pickup threshold and time delay, shorttime pickup threshold and time delay, instantaneous pickup, and ground fault pickup threshold and time delay.

Protection and coordination

Equipment protection and coordination can be competing objectives of the system designer, when applied within their electrical ratings circuit breakers will safely protect both themselves and the electrical system. Selective coordination is necessary when continuity of service is desired. This is often achieved through the use of the circuit breaker’s short-time ratings. An intentional tripping delay may be applied only when downstream circuit breakers have an adequate short-time current rating or are self-protecting.

For many applications in low-voltage power distribution systems, a lesser short-time current rating may be acceptable; but, for applications such as a main circuit breaker in a service entrance switchboard or switchgear, it may not be. A low-voltage power circuit breaker used as a main circuit breaker that has a 65 kA short-time current rating would allow the flexibility to coordinate with downstream circuit breakers for a fault of any magnitude up to the full 65 kA short circuit current rating of the circuit breakers and switchgear.

Proper selection of LVPCBs is critical to the performance of the electrical system. Choosing circuit breakers with an appropriate short-circuit current rating and short-time current rating provides the opportunity to have a selectively coordinated system up to high fault current levels.

Emax 2 Circuit Breaker Ratings

[1] IEEE C37.20.10 – 2016, IEEE Standard Definitions for AC (52 kV and below) and DC (3.2 kV and below) Switchgear Assemblies [2] IEEE C37.20.1 – 2015, IEEE Standard for Metal-Enclosed Low-Voltage (1000 Vac and below, 3200 Vdc and below) Power Circuit Breaker Switchgear [3] ANSI C37.50 – 2018, Low Voltage AC Power Circuit Breakers Used in Enclosures— Test Procedures [4] ANSI C37.51 – 2018, Metal-Enclosed Low-Voltage AC Power Circuit Breaker Switchgear Assemblies— Conformance Test Procedures [5] UL 1066, Fourth Edition, Low-Voltage AC and DC Power Circuit Breakers Used in Enclosures

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Check out more on power circuit breakers: Emax 2 circuit breakers on ABB website

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This site is created by ABB application engineers and experts as an educational tool to help engineers.

Selectivity techniques

The different selectivity techniques, also from the operational point of view.

Selectivity (discrimination) is achieved by automatic protective devices when a fault is cleared by the protection device installed immediately upstream of it, while all the other protection devices remain unaffected.

Two areas can be defined, depending on the current ranges and circuit-breaker trip curves:

In which the thermal protection for thermal-magnetic trip units and protection L for electronic trip units are normally called upon to trip.

In which the magnetic protection for thermal-magnetic trip units or protections S, D and I for solid-state trip units are normally called upon to trip.

Time-current selectivity

Current selectivity, time selectivity, energy selectivity, zone selectivity.

The protections against overload generally have a definite time characteristic, whether they are realized by means of a thermal trip unit or by means of function L of an electronic trip unit. By definite time characteristic we mean a trip characteristic for which, as the current increases, the trip time of the circuit-breaker decreases.

When there are protections with this type of characteristics, the selectivity technique used is time-current selectivity. Time-current selectivity realizes trip selectivity by adjusting the protections so that the load-side protection, for any possible overcurrent value, trips more rapidly than the supply-side circuit-breaker.

When the trip times of the two circuit-breakers are analyzed, it is necessary to consider:

• ​The tolerances over the thresholds and trip times;
• ​The real currents circulating in the circuit-breakers.

With regard to tolerances, ABB SACE makes the trip curves of its trip units available in the technical catalogues and in DOCWin software. In particular, in the curve module of DOCWin, the curves of both the electronic and thermomagnetic trip units include the tolerance values. Thus, a trip of the protection unit is represented by two curves, one showing the highest trip times (top curve), and the other one indicating the most rapid trip times (bottom curve).

• the supply-side circuit-breaker trips according to its own bottom curve.
• the load-side circuit-breaker trips according to its own top curve.
• if the two circuit-breakers are passed through by the same current, it is sufficient that there is no overlapping between the curve of the supply-side circuit-breaker and of the load-side circuit-breaker;
• if the two circuit-breakers are passed through by different currents, it is necessary to select a series of significant points on the time current curves and check that the trip times of the supply-side protection are always above the corresponding times of the load side protection.
• 1.05 x I1 1 of the supply-side circuit-breaker (value below which the supply-side protection never trips)
• 1.20XI3 (or I2) 2 of the load-side circuit-breaker (value above which the load-side protection certainly trips with the protections against short-circuit).

• 1.05 is the value for minimum definite non-intervention defined in the Standard (IEC60947-2). For some types of circuit-breakers this value could vary (see the technical catalogue for further information).
• 1.2 is the value for maximum definite intervention for protection against short-circuit defined in the Standard (IEC60947-2). For some types of circuit-breakers, this value might be lower (see the technical catalogue for further information).

This type of selectivity is based on the observation that the closer the fault point to the power supply source of the installation, the higher the short-circuit current. Therefore, it is possible to discriminate the zone where the fault occurs, by setting the instantaneous protections to different current values.

Total selectivity can normally be achieved in specific cases only where the fault current is not high and where there is a component with high impedance interposed between the two protections (transformer, very long cable or a cable with reduced cross-section, etc.), and consequently there is a great difference between the short-circuit current values.

Therefore, this type of coordination is used above all in final distribution (low rated current and short-circuit current values, and high impedance of the connection cables). The time-current trip curves of the devices are normally used for this study. It is intrinsically fast (instantaneous), easy to realize and cost-effective.

• The ultimate selectivity current is usually low and therefore selectivity is often partial;
• The setting level of the protections against overcurrent rises rapidly;
• It is impossible to have redundancy of protections, which guarantees that the fault is cleared rapidly if one protection fails to operate.

This type of selectivity can also be realized between circuit-breakers of the same size not providing time-delayed overcurrent protection (S).

• The protection against short-circuit of the supply-side circuit-breaker A shall be set to such a value that it does not trip for faults occurring on the load side of protection B. (In the example in the figure I3 minA > 1kA)
• The protection of the load-side circuit-breaker B shall be set to such a value that it trips for faults occurring on its load side. (In the example in the figure I3 MaxB < 1kA)

Obviously, the setting of the protections must take into account the real currents circulating in the circuit-breakers.

This selectivity limit, associated to the magnetic threshold of the supply-side circuit-breaker, is exceeded in all cases where energy type selectivity is realized. If the settings indicated for energy selectivity are respected, for the combinations of circuit-breakers with an energy selectivity value given in the coordination tables published by ABB, the selectivity limit to be taken into consideration is the one given in the tables and not the one obtained by using the above mentioned formula.

The ultimate selectivity value that can be obtained is equal to the instantaneous trip threshold of the supply-side protection minus any tolerance value. Is = I3 minA

This type of selectivity is a development of the previous one. For this type of coordination, in addition to the current trip threshold, a trip time is also defined: a certain current value will make the protections trip after a defined time delay, such as to allow any protection placed closer to the fault to trip, excluding the area of the fault. Thus, the setting strategy is to increase gradually the current thresholds and the trip delays by getting closer to the power supply sources (setting level directly correlated to the hierarchical level). The delayed trip thresholds must take into account the tolerances of the two protection devices and the effective currents flowing through them.

The difference between the delays set for the protections in series must take into account the times of fault detection and clearance of the device on the load side and of the inertia time (over-shoot) of the device on the supply side (time interval during which the protection can trip even when the phenomenon is over). As in the case of current selectivity, the study is made by comparing the time-current trip curves of the protection devices.

Speaking generally, this type of coordination:

• is easy to study and realize;
• is not very costly as regards the protection system;
• allows even high selectivity limit values to be obtained (if Icw is high);
• permits redundancy of the protection functions.
• the trip times and energy levels let through by the protections, especially by those close to the sources, are high.

This type of selectivity can also be realized between circuit-breakers of the same size, equipped with electronic trip units providing time-delayed overcurrent protection.

The protections against short-circuit of the two circuit-breakers will be set:

• With the I 2 trip thresholds against time-delayed short-circuit set so as not to create trip overlapping, taking into consideration the tolerances and the real currents circulating inside the circuit-breakers;
• With t 2 trip times set so that the load-side circuit-breaker B clears the fault, whereas the supply-side circuit-breaker A , still in its timing phase, manages to "see" the extinction of the current and thus remains closed.

The ultimate selectivity limit obtained is equal:

• To the instantaneous trip threshold of the supply-side protection, if this function is enabled, minus the tolerance (if any): Is = I3 minA
• To the Icw value for supply-side air circuit-breakers when the instantaneous protection function is set to OFF.

Note These selectivity limits are exceeded in all the cases where energy type selectivity is realized. If the settings indicated for energy selectivity are respected for the combinations of circuit-breakers with an energy selectivity value given in the coordination tables published by ABB, the selectivity limit to be taken into consideration is the one given in the tables, and not the one that can be obtained from the considerations in this paragraph.

The coordination of the energy type is a particular type of selectivity that exploits the current-limiting characteristics of moulded-case circuit-breakers. It is recalled that a current-limiting circuit-breaker is "a circuit-breaker with a break-time short enough to prevent the short-circuit current reaching its otherwise attainable peak value" (IEC 60947-2). In fact, all the ABB SACE moulded-case circuit-breakers of the Tmax series, the miniature circuit-breakers and the air current-limiting circuit-breaker E2L and E3L have more or less marked current-limiting characteristics. Under short-circuit conditions, these circuit-breakers are extremely fast (trip times in the range of a few milliseconds) and open when there is a strong asymmetrical component. Thus, it is impossible to use the time-current trip curves of the circuit-breakers, obtained with symmetrical sinusoidal types of wave forms, for the coordination study.

These phenomena are mainly dynamic (therefore proportional to the square of the instantaneous current value) and are heavily dependent on the interaction between the two devices in series. Therefore, the end user cannot determine the energy selectivity values. The manufacturers provide tables, slide-rules and calculation programs giving the ultimate current selectivity values of I s under short-circuit conditions for different combinations of circuit-breakers. These values are defined by theoretically integrating the results of tests carried out in compliance with the prescriptions in Annex A of Std. IEC 60947-2.

The short-circuit protections of the two circuit-breakers shall observe the conditions below.

• Supply-side thermomagnetic trip unit
• Supply-side electronic trip unit

The ultimate selectivity limit Is obtained is the one given in the tables ABB SACE makes available for its customers.

This type of coordination is an evolution of time coordination. In general, zone selectivity is realized by means of dialogue between the current measuring devices that, once the setting threshold has been detected as having been exceeded, allows the fault zone to be identified correctly and the power supply to the fault to be cut off.

It can be realized in two ways:

• The measuring devices send the information on the current setting threshold having been exceeded to a supervision system and the latter identifies which protection has to intervene;
• When there are current values exceeding their setting, each protection sends a lock signal by means of a direct connection or a bus to the hierarchically higher level protection (on the supply side in relation to the power flow direction) and, before intervening, checks that a similar lock signal has not arrived from the load-side protection. Thus, only the protection immediately on the supply side of the fault trips.

This second way guarantees without doubt shorter trip times. Compared with a coordination of the time type, the need to increase the intentional delay as one moves towards the power supply source is no longer necessary. The delay can be decreased to the time needed to exclude the presence of a possible lock signal coming from the load-side protection.  This type of selectivity is suitable for radial networks and, when associated with directional protection, is suitable for meshed networks too.

Compared with the coordination of time type, zone selectivity permits:

• a reduction in the trip times (these can be lower than hundred milliseconds);
• a reduction both in the damage caused by the fault and in the interferences in the power supply system;
• a reduction in the thermal and dynamic stresses on the components of the installation;
• a very high number of selectivity levels.
• it is more burdensome both in terms of cost and of complexity of the installation;
• it requires an auxiliary supply.

As a result, this solution is mainly used in systems with high rated current and short-circuit current values and with binding requirements for safety and service continuity. In particular, examples of logical selectivity are often found in the primary distribution switchgear placed closely on the load side of transformers and generators.

This type of selectivity can be realized:

• between Emax 2 air circuit-breakers equipped with Ekip Touch and Ekip Hi-Touch trip units. The ultimate selectivity limit which can be obtained is equal to the Icw Is = Icw
• between Tmax T4L,T5L and T6L moulded-case circuit-breakers equipped with PR223 EF trip units. The ultimate selectivity limit which can be obtained is 100kA Is = 100kA

Then, by means of S51/P1 contact module, it is possible to make a chain of zone selectivity between Tmax and Emax 2. It is also possible to realize a selectivity chain including ABB MV protections.

Operating principle of zone selectivity between ABB circuit-breakers:

• In the presence of current values higher than their setting, each protection sends a lock signal (by means of a direct connection or a bus) to the hierarchically higher level protection (on the supply side in relation to the power flow direction) and, before tripping, checks that an analogous lock signal has not arrived from the load-side protection. In this way, only the protection immediately on the supply side of the fault trips.

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Tripping Time of a Circuit-Breaker. Definition & Meaning

Tripping time: the time interval from the instant at which the associated tripping current begins to flow in the main circuit to the instant when this current is interrupted (in all poles) [this term is defined in the IEC 60050-442].

Note 1 to entry: For circuit-breakers “opening time” is commonly referred to as “tripping time”, although, strictly speaking, tripping time applies to the time between the instant of initiation of the opening time and the instant when the opening command becomes irreversible.

Note 2 to entry:

• in the case of a directly operated circuit-breaker, the instant of initiation of the opening time is the instant of initiation of a current large enough to cause the circuit-breaker to operate;
• in the case of a circuit-breaker operated by any form of auxiliary power, the instant of initiation of the opening time is the instant of application or removal of the auxiliary power to the opening release.

The moment of tripping time initiation is the moment in time when the electric current in the main circuit of the circuit breaker reaches the value at which its overcurrent release device trips.

The moment in time when the trip command becomes irreversible is the moment when the overcurrent release actuates the circuit breaker’s holding device and induces the opening of its main contacts. Therefore, the tripping time is actually the time interval between the moment when the electric current in the circuit breaker’s main circuit reaches the tripping level of its overcurrent release and the moment when the overcurrent release trips.

Tripping Time Setting of Overcurrent Releases

The tripping time shall be stated as follows, depending on the type of over-current release:

1) Definite time-delay overcurrent releases .

The time-delay of such releases is independent of the over-current. The tripping time setting shall be stated as the duration in seconds of the opening time of the circuit-breaker, if the time-delay is not adjustable, or the extreme values of the opening time, if the timedelay is adjustable.

2) Inverse time-delay overcurrent releases .

The time-delay of such releases is dependent on the overcurrent.

The time-current characteristics shall be given in the form of curves supplied by the manufacturer. These shall indicate how the opening time, starting from the cold state, varies with the current within the range of operation of the release. The manufacturer shall indicate, by suitable means, the tolerances applicable to these curves.

These curves shall be given for each extreme value of the current setting and, if the time setting for a given current setting is adjustable, it is recommended that they be given in addition for each extreme value of the time setting.

It is recommended that the current be plotted as abscissa and the time as ordinate, using logarithmic scales. Furthermore, in order to facilitate the study of co-ordination of different types of overcurrent protection, it is recommended that the current be plotted as multiples of the setting current and the time in seconds on the standard graph sheets detailed in 5.6.1 of IEC 60269-1:2006.

Standard Time-Current Zone

The tripping characteristic of circuit-breakers shall be such that they ensure adequate protection of the circuit, without premature operation.

The zone of the time-current characteristic (tripping characteristic) of a circuit-breaker is defined by the conditions and the values stated in Table 1.

This table refers to a circuit-breaker mounted in accordance with the reference conditions operating at the reference calibration temperature of 30 °C, with a tolerance of +5 °C.

The test may be made at any convenient temperature, the results being referred to 30 °C, using the information given by the manufacturer.

In any case the variation from the test current of Table 1 shall not exceed 1,2 %/ per K of calibration temperature variation. If the circuit-breakers are marked for a calibration temperature different from 30 °C, they are tested for that different temperature. The manufacturer shall be prepared to give information on the variation of the tripping characteristic for calibration temperatures differing from the reference value.

A current equal to 1,13 I n (conventional non-tripping current) is passed for the conventional time through all poles, starting from cold (see Table 1).

Moreover the circuit-breakers shall trip within the time corresponding to the test c of Table 1 when a current equal to 2,8 I n is passed through all poles, the lower time limit being 0,1 s instead of 1 s.

NOTE. An additional test, intermediate between c and d, is under consideration for circuit-breakers of type D.

a The term “cold” means without previous loading. b 50 I n for special cases.

About The Author

Dmitry Makarov

Breaker Keeps Tripping: Understanding the Common Causes and Solutions

When a circuit breaker trips, it protects your device and circuit; it’s just doing its job unless it is damaged.

Do you notice that sometimes the lights of a residential place go off due to circuit breaker tripping, or sometimes the fuse blows up? It is due to some faults in the electrical network. I see these faults too much because I work as an electrical maintenance engineer.

I will discuss different reasons that cause circuit breaker tripping. I won’t rely only on my long work experience as an engineer, which is now about 15 years, but also I will provide you with the results of deep searching about circuit breaker tripping.

Table of Contents

How To Find The Reason Behind Tripping My Circuit Breaker?

Tripping of a circuit breaker can occur due to various reasons, such as overloading, short circuits, ground faults, or issues with the electrical appliances or wiring. Here are some steps to help you identify the reason behind the tripping:

Identify the Circuit: Determine which circuit breaker has tripped and which area of the house or building is affected. This can help narrow down the potential causes.

Unplug Appliances: If the tripping occurs when a specific appliance is used, unplug that appliance and try resetting the circuit breaker. If the breaker does not trip, the appliance might be faulty and cause an overload.

Check for Overloading: Assess whether the circuit is overloaded by connecting too many high-powered devices to the same circuit. Try redistributing the load by connecting devices to different circuits.

Inspect for Short Circuits: Examine the electrical outlets, switches, and wiring for signs of damage or exposed wires that could be causing a short circuit. If you notice any issues, consult a qualified electrician to repair or replace the affected components.

Look for Ground Faults: Ground faults occur when a hot wire comes into contact with a ground wire or a metal wall box. Use a ground fault circuit interrupter (GFCI) tester to identify any potential ground fault issues and address them accordingly.

Check for Wet Conditions: If the circuit is in a damp or wet area, it could lead to a ground fault. Ensure that all electrical components in such areas are moisture-resistant and properly grounded.

Inspect the Breaker Itself: Examine the circuit breaker for any signs of damage, corrosion, or overheating. If you notice any issues, consider replacing the circuit breaker with a new one.

Consult a Professional Electrician: If you are unable to identify the cause of the tripping or if you suspect a more complex electrical issue, it is advisable to consult a licensed electrician. They can conduct a comprehensive inspection of the electrical system and troubleshoot any underlying problems.

It is crucial to prioritize safety when dealing with electrical issues. If you are unsure about how to proceed or are not comfortable handling electrical components, it is best to seek professional assistance to ensure a safe and effective resolution to the problem.

What would cause a circuit breaker to keep tripping?

Now, after this quick discussion for non-technical persons. let’s move to the electrical engineering discussion.

Overloaded Circuit:

One of the main reasons for circuit breaker tripping is the overloaded circuit in the electrical system. When many loads are connected to the circuit, the circuit attempts to draw a greater electrical load than its rated value. Due to this, the circuit breaker heats up, and the breaker tripping occurs.

Electrical Short Circuit:

Another reason for the breaker tripping is the electrical short circuit. A short circuit occurs due to low insulation resistance .

When the positive and negative (live and neutral) terminal connects with each other in the absence of any resistance. This causes an unimpeded flow of electricity. A large amount of current flows through a breaker that causes tripping.

It is worth mentioning here how to decide whether the tripping occurs due to a short circuit . The answer is clear and simple. If a circuit breaker trips instantly again and again after you reset it, the tripping occurs due to a short circuit.

How Do I Know That I Have a Short Circuit at the House? If you find fuses being blown regularly or a circuit breaker tripping frequently, it might be a symptom of a short circuit.

A fuse will usually explode, or a circuit breaker will trip instantly. If a new fuse with the proper rating also blows, you’ve got a short circuit.

If a circuit breaker is reset and it trips again instantly, as you connect it, you have a short circuit or a broken circuit breaker. Read my detailed article about Electrical short circuits, why is it dangerous?

Ground Fault:

Another reason that causes the circuit breaker tripping is the ground fault. A ground fault is a type of short circuit when a hot wire comes in contact with the ground or any other type of metal.

The ground fault causes an increase in the flow of current. It causes the circuit breaker to heat up and as a result, circuit breaker tripping occurs.

Some ground faults are not detectable by normal MCB. So it’s recommended to use GFCI (ground fault circuit interrupter) This is better for human safety as this breaker can detect small milli-amperes and trips before a shock happens. Read my article on my other site: Surge Protectors and GFCI Outlets: Can They Safely Coexist?

When fluctuation or sparking occurs between two-wire connections at a point. Arc faults occur.

Sometimes the screws at a point become loose, In this case, AFCI (arc fault circuit interrupter) is recommended.

While the circuit breaker is an Arc fault interpreter (AFCI ). It detects the early wiring problem and trips in advance to stop the flow of a large amount of current.

Bad Circuit Breaker:

Sometimes the circuit and loads are all OK and in good condition. But the breaker keeps tripping randomly.

This is a sign that the circuit breaker is bad. Like any device, breakers have a lifetime, and then breakers go bad . And it’s time to replace it.

The circuit breaker keeps tripping immediately

If your circuit breaker keeps tripping immediately after resetting it, this indicates a severe electrical issue that requires prompt attention. Here are some steps to follow to address the problem:

Identify the Problem Circuit: Determine which specific circuit is causing the repeated tripping. This can help pinpoint the area of concern and focus your troubleshooting efforts.

Disconnect All Appliances: Unplug or disconnect all devices and appliances from the circuit that keeps tripping the breaker. If the breaker doesn’t trip after disconnection, the issue may be related to one of the appliances or devices.

Check for Short Circuits or Ground Faults: Inspect the wiring, outlets, and switches for signs of damage, exposed wires, or any moisture intrusion. Focus on the affected circuit and look for any visible signs that might indicate a short circuit or ground fault.

Examine the Breaker Itself: Check the circuit breaker for any signs of damage, overheating, or wear. A faulty breaker could be the root cause of the repeated tripping. Consider replacing the circuit breaker with a new one if it appears damaged.

Consult a Professional Electrician: If you are unable to identify the cause of the immediate tripping, or if the issue persists despite your troubleshooting efforts, it is essential to seek assistance from a qualified electrician. They can perform a comprehensive inspection of the electrical system and troubleshoot the problem effectively.

It is crucial to prioritize safety when dealing with electrical issues. If you are uncertain about how to proceed or are uncomfortable handling electrical components, it is best to seek professional help.

Electrical problems can be complex and potentially dangerous, so it is important to have them addressed by a licensed electrician to ensure the safety of your property and its occupants.

Can a circuit breaker trip for no reason?

A breaker will trip for no reason if it malfunctions . A breaker will trip when a short circuit occurs on an electrical circuit, causing sparks, popping sounds, or smoke to be produced.

A loose connection, slipping wire, or even damage from animals chewing on cables could cause this.

If you didn’t find any faults like a short circuit , overload, or lost connection, your circuit breaker might be old and unable to carry current anymore.

In other words, it has become bad. It would be best if you replaced it for the circuit to continue operating.

Why is the circuit breaker tripping without load?

If your circuit breaker trips without loads, a wire with damaged insulation somewhere in the electrical panel or in power outlets can be the cause of breaker tripping and will continue to do so until you fix it .

A general wiring issue can potentially be the reason why a circuit breaker trips. You can have obsolete wiring if your home is older.

The issue with older electrical systems is that new technology and appliances frequently demand more power than previous systems can safely handle.

The older wiring can’t keep up with the increasing demands as our daily energy needs increase. This may be the problem if several breakers are often tripping without a load. Otherwise, there can be a problem with the breaker panel itself.

When your breaker trips without any load being present, you should take into consideration the following three wiring problems:

Current Leakage: One possibility is that one or more of the input wires have current leakage, which causes the circuit breaker to trip even when there isn’t a load attached to it. If so, your annoying issue is taking place for your own benefit. tripping is a precaution for the safety of your all-electrical devices.

Damaged Wires : Not simply the input cables might be damaged; it could happen everywhere. They could have been accessed by pests or insects that, only by gnawing, caused significant harm. This kind of issue may be sufficient to trigger a breaker trip even with no loads.

A Loose Wire in an Outlet : This loose wiring issue may be pretty frustrating. In other words, a loose wire in one of your outlets will keep your breaker continuously tripping. If you have a GFCI outlet, this is a very typical issue (Ground-Fault Circuit Interrupter).

Why shouldn’t you reset a tripped circuit breaker immediately?

The straightforward answer is that you shouldn’t reset a circuit breaker unless you are sure of the reason for the fault and that it poses no danger.

Note that if you reset it immediately it may trip again in case it is still hot, even if the fault is cleared.

Circuit breakers are there to safeguard your family, your house, and yourself. When a circuit breaker trips, it indicates that a current greater than the trip current is passing through it.

In case of a faulty circuit or wires, or a short circuit, the circuit breaker will trip again immediately if you reset it.

The short circuit current makes the circuit breaker get hot and trip, it should be cooled before you reset it.

Can a tripped breaker stop a fire?

Yes, if tripping happen before the fire catch wires or panel. But it won’t if tripping happens after the fire catch wires or panel .

There can be two scenarios, 1 st one is before the wiring or breaker panel catches fire.

And 2 nd is the role of the circuit breaker after catching fire let’s explore both scenarios in detail below:

Role of circuit breaker before Catch Fire :

Tripped circuit breakers can prevent fire and protect electrical systems against overloads and short circuits, circuit breakers assure electrical safety in homes, offices, and other buildings as well as for industrial uses.

The circuit breaker instantly shuts off the electrical circuit when a problem is found, protecting the wires and reducing the chance of catching fire.

Role of circuit breaker after catching fire:

Tripped circuit breakers didn’t play any role and could not provide safety to the system after catching fire.

If the circuit breaker is not tripped due to any reason or sometimes the fault current is too much bigger than the rating of the cable, then the circuit breaker wiring or panel box catches fire.

Can tripping circuit breaker damage your devices?

Tripping circuit breakers themselves do not typically cause direct damage to your electrical devices.

In fact, the primary purpose of a circuit breaker is to protect your devices and electrical system from potential damage due to electrical overloads or short circuits.

When a circuit is overloaded or a short circuit occurs, the circuit breaker is designed to trip and cut off the flow of electricity, preventing excessive current from damaging your devices and wiring.

However, frequent or repetitive tripping of circuit breakers may indicate underlying issues within the electrical system that could potentially affect connected devices. Repeated tripping may point to problems such as overloading, short circuits, ground faults, or other electrical faults that could impact the functionality and safety of your devices.

Indirectly, sudden loss of power due to a tripped circuit breaker can cause data loss or corruption in electronic devices like computers, especially if they are not connected to an uninterruptible power supply (UPS). Additionally, frequent power fluctuations resulting from faulty electrical systems can gradually wear down sensitive electronic components, reducing the lifespan of your devices over time.

To prevent potential damage to your devices, it’s important to address any electrical issues promptly. If you notice persistent circuit breaker trips, it’s advisable to consult a qualified electrician to identify the underlying cause and ensure that your electrical system is functioning safely and efficiently. Taking proactive steps to maintain your electrical system can help prevent potential damage to your devices and ensure the safety of your property.

Why is the Main circuit breaker tripping?

The main breaker can trip for a variety of reasons. Whether it be a lightning strike, a power surge from the utility company, or an overload to the electrical panel, the main breaker can be tripped due to any of these factors.

Furthermore, the main circuit breakers can trip simply because they’re worn out . There might be a situation when a branch circuit breaker fails and is no longer capable of tripping as designed, which may result in the main breaker tripping to provide secondary safety shutoffs in the event that the individual circuit breaker fails. 

Furthermore, If the total load demand becomes too much or if there is any significant issue with the electrical system, the main breaker cuts off electricity to the entire house.

These issues often entail brief power spikes, although it may be necessary to detect system issues occasionally.

The main circuit breaker “tripping” is somewhat uncommon since often, individual circuit breakers trip long before the main breaker has to shut down.

Does weather affect the circuit breaker?

Yes, weather affects the circuit breakers . In response to the heat generated by the circuit breaker, the bimetallic strip inside the breaker flexes and trips the breaker.

The hot weather also can cause a breaker to trip, it all depends on the thermal effect of heat that causes the bimetallic strip inside the breaker to flex and trip it.

On the other hand, as compared to hot weather, cold weather didn’t affect the circuit breaker as much as lead to tripping, but if there is a foggy season and too much moisture in the environment, that can cause tripping the breaker.

A breaker’s components can also be adversely affected by the ambient heat in the air surrounding the breaker. A circuit breaker should typically not be heated over 140°F. If it happens, it indicates a potential trip of the circuit breaker.

If you can’t keep your finger on the plastic portion of the circuit breaker without being burnt, it’s too hot, according to a reliable “rule of thumb.”

Why do my breakers trip when it rains?

The main cause of a breaker’s trip after the storm is a short circuit brought on by water .

Due to heavy rain, the electrical wire isolation may deteriorate after water exposure, causing a short circuit. Improper panel box installation might be another reason your circuit breaker tripped during the storm.

Rainwater may get into your circuit in a number of ways if the main line is not installed properly.

Water may enter your wiring conduits through the wire leading to the meter and electrical circuit. It’s also conceivable that the conduit or hose you used to install your main line will let water through.

Because of this, if the breaker box is in the basement, water may wet your circuit. The worst possible scenario for your house is a wet circuit breaker.

A wet circuit is dangerous because you might get electrocuted in addition to the electrical problems it can create.

Can you reset a breaker in the rain?

It is generally not recommended to reset a circuit breaker while it is raining or in wet conditions . Water can significantly increase the risk of electrical hazards, potentially leading to electric shocks or other safety risks.

Resetting a circuit breaker in the rain could expose you to electrical currents and pose a danger to your safety.

To ensure your safety when dealing with electrical components, including circuit breakers, it’s crucial to follow these guidelines:

• Safety First: Prioritize your safety at all times. Do not attempt to handle electrical components in wet conditions or when you are standing on a wet surface.
• Turn Off the Main Power: If you need to access the circuit breaker panel during wet conditions, make sure to turn off the main power to the house or the affected circuit before attempting any reset.
• Wait for Dry Conditions: If the circuit breaker trips during the rain, it is advisable to wait until the weather improves and the area is dry before attempting to reset it.
• Take Precautionary Measures: If you must work on electrical components in damp conditions, wear appropriate personal protective equipment (PPE) such as rubber gloves, rubber-soled shoes, and other safety gear to minimize the risk of electrical shock.

If you are unsure about how to safely handle a circuit breaker or if you are uncomfortable with electrical work, it is best to seek assistance from a qualified electrician.

Professional electricians have the necessary expertise and equipment to handle electrical components safely, even in adverse weather conditions.

Prioritizing safety is essential to prevent accidents and ensure the protection of both you and your property.

Can a storm and lightning cause a CB to trip?

Yes, storms and lightning can potentially cause a circuit breaker to trip. Lightning strikes can induce power surges in electrical systems, leading to a sudden increase in electrical current that exceeds the circuit breaker’s capacity.

In response to the excessive current, the circuit breaker will trip, cutting off the power supply to the affected circuit or the entire house to prevent electrical damage or fire hazards.

Additionally, storms can cause power fluctuations and electrical disturbances, which might impact the stability of the electrical supply. These fluctuations can result in overloading or short circuits within the electrical system, leading to the tripping of the circuit breakers.

To protect your electrical system during storms and lightning, consider taking the following precautions:

• Install Surge Protectors: Use surge protectors to safeguard sensitive electronic devices from power surges caused by lightning strikes or other electrical disturbances.
• Unplug Electronic Devices: Unplug sensitive electronic devices during thunderstorms to prevent potential damage from power surges or lightning strikes.
• Invest in Lightning Protection Systems: Consider installing lightning protection systems, such as lightning rods and surge arresters, to divert lightning strikes away from your property and protect your electrical system.
• Maintain the Electrical System: Regularly inspect and maintain your electrical system to ensure that it is in good condition and capable of withstanding electrical disturbances caused by storms and lightning.

If you experience frequent circuit breaker trips during storms or if you suspect damage to your electrical system as a result of a lightning strike, it is advisable to seek the assistance of a licensed electrician.

A professional electrician can assess the condition of your electrical system, identify any potential issues, and implement necessary measures to safeguard your property from electrical hazards.

Will a breaker trip if wires touch each other?

Yes, a circuit breaker can trip if wires touch each other, especially if the wires create a short circuit.

When wires make direct contact or create a path with low resistance between the hot and neutral wires or between the hot wire and the ground, a short circuit occurs.

This causes a sudden increase in electrical current, exceeding the circuit breaker’s capacity and triggering it to trip.

The purpose of a circuit breaker is to protect the electrical system and connected devices from potential damage caused by overcurrent situations like short circuits. When the circuit breaker trips due to a short circuit, it interrupts the flow of electricity and prevents further damage to the wiring, appliances, and other electrical components.

To prevent wires from touching and causing a short circuit, it’s essential to follow proper wiring practices, including:

• Using appropriate wire connectors and junction boxes to secure and protect wire connections.
• Insulating exposed wires to prevent contact with other wires or conductive materials.
• Maintaining proper wire spacing and organization to minimize the risk of accidental contact.

If you suspect that wires are touching or if you experience frequent circuit breaker trips, it’s essential to consult a licensed electrician to inspect your electrical system.

A professional electrician can identify any potential wiring issues, troubleshoot the cause of the tripping, and ensure the safety and functionality of your electrical system.

Can the circuit breaker trip if you hold it?

The circuit breaker standard UL489 requires circuit breakers to be “trip free”. A trip-free circuit breaker will still trip if you hold it in the ON position.

Yes, you can hold the toggle up, but that does not stop the breaker from tripping under an over-current condition.

A circuit breaker cannot be forced if it trips repeatedly; it will keep opening and burn out.

It is usually not harmful to have a momentary connection, as it will only last for a short time.

You will need to resolve the problem causing the trip and then you will need to replace the circuit breaker if it went bad.

Why is the circuit breaker not tripping?

The circuit breaker may not trip if it malfunctions due to (an entirely mechanical problem, or sustains partial or total damage ) Occasionally, a circuit breaker will not trip in circumstances of fault like a short circuit, or overload, indicating it is bad and must be replaced.

It is also possible for the cause of the problem to be entirely mechanical, which means there may be a physical switch that is stuck in the “on” position.

The circuit breaker may also malfunction without tripping if it sustains partial or total damage. On occasion, a power failure occurs as internal components melt. To ensure appropriate operation, examine the circuit breaker and replace the broken one.

Signs of damaged/ faulty circuit

• Inspect the circuit breakers for any burning odors.
• If the panel feels hot to the touch, the circuit is either broken or overloaded.
• If the circuit is beyond its prime or is too old, replace it with a new one.
• Parts become melted or scorched due to heat.
• The item is defective if it trips off more frequently while gadgets draw more power.

What happens if a breaker doesn’t trip in faults condition?

If a circuit breaker fails to trip during a fault condition, it can lead to various hazardous situations, including:

• Overheating and Fire Risk: When a circuit experiences an overload or short circuit, excessive current flows through the wires, leading to overheating. If the circuit breaker does not trip to interrupt the flow of current, the wires, insulation, or other electrical components can overheat and potentially ignite a fire.
• Equipment Damage: The excessive current in the circuit can damage connected electrical devices, appliances, and other equipment. Without the protection of the circuit breaker, the electrical components can sustain irreparable damage, leading to costly repairs or replacements.
• Electrocution and Safety Hazards: In the absence of circuit protection, the risk of electric shock or electrocution increases, especially if someone comes into contact with live wires or faulty electrical equipment.
• Damage to the Electrical System: Continual overloading or short circuits without interruption from the circuit breaker can cause significant damage to the overall electrical system, including the wiring, panels, and other connected components. This can lead to extensive repairs and pose a safety risk to the property.

To mitigate the risks associated with a circuit breaker failing to trip during a fault condition, it is crucial to regularly inspect and maintain the electrical system. Consider the following measures:

• Schedule Regular Inspections: Arrange for periodic inspections of the electrical system by a qualified electrician to ensure that the circuit breakers are functioning correctly.
• Test the Circuit Breakers: Conduct routine tests on the circuit breakers to verify that they trip appropriately during overload or short circuit situations.
• Upgrade to Advanced Protection: Consider installing advanced protection devices, such as ground fault circuit interrupters (GFCIs) and arc fault circuit interrupters (AFCIs), to enhance the safety and reliability of the electrical system.

Prioritizing regular maintenance and promptly addressing any issues with the circuit breakers or the electrical system can help prevent hazardous situations and ensure the safety and functionality of your property.

Is the circuit breaker tripping a good or bad thing?

Yes, circuit breaker tripping is good from the perspective of the safety of your home and home appliances .

It also provides protection against dangerous electrical fire hazards due to short circuits and overloading as long as it is not a bad CB .

But sometimes, apparently, you didn’t see any issue, but your circuit breaker keeps tripping and can get you in trouble.

It can be due to wiring issues like too much old wiring, damaged cables, or loose cable connection, which is difficult to troubleshoot because you have to check all the outlet’s wiring connected to the breaker.

That can be time-consuming, but it’s necessary to troubleshoot the fault and rectify it as soon as possible to avoid any bigger damage or loss.

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Three surfers on a dream trip to Mexico were brutally killed. Here’s what we know

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A trio of tourists on a surfing trip in Mexico were living an idyllic life. They were posting photos of themselves on the beach, on rooftops, drinking beer, listening to music as they explored the country’s scenic coastline.

Then, they disappeared.

Here’s what we know about what happened:

Who were they?

The men who were killed were Australian brothers Callum Robinson, 33, his brother Jake, 30 , and their American friend Jack Carter Rhoad, 30.

Callum was a high-level lacrosse player. He played Division III college lacrosse at Stevenson University in Maryland.

World & Nation

Bodies found in Baja California during search for missing tourists, Mexican officials say

Mexican officials say three bodies are found in the Baja California area where two Australian brothers and their American friend went missing while on a surf trip.

May 4, 2024

“He lived an extraordinary life, but what is most impressive about Callum is what a loyal friend he was. Once you were his friend, you were friends for life,” said Stevenson University lacrosse team coach Paul Cantabene.

“My heart is shattered into a million pieces,” wrote Callum Robinson’s girlfriend, Emily Horwath, in an Instagram post.

His brother Jake was a doctor, and Jack Carter Rhoad founded an online apparel company in San Diego called Loma Apparel. He also worked for a consulting company called ITCO Solutions.

Rhoad had recently proposed to his girlfriend, and his final Facebook post, from July 2023, showed pictures of the proposal.

What were they doing in Mexico?

The three men were on a surfing trip in Baja California and were expected to check into an Airbnb in Rosarito on April 27 but never showed up, according to Debra Robinson, Callum and Jake’s mother.

The three arrived in Mexico on April 26 for their idyllic beachside trip. Callum Robinson posted photos of the trio drinking beer on a rooftop, as well as pictures of the men at the beach and in a rooftop Jacuzzi.

3 bodies in Mexican well identified as Australian and American surfers killed for tires

Mexican authorities say three suspects killed two Australians and an American on a surfing trip in Baja California to steal tires from their truck.

May 5, 2024

Their disappearance triggered a manhunt and investigation by local Mexican police, the FBI and the Mexican marines.

What happened?

Mexican authorities have determined that the three men were killed by thieves who were looking to steal their white pickup truck in order to sell its tires.

The Chevrolet truck was posted in the first picture Callum Robinson shared when the men arrived in Baja California on April 26. It had a California license plate.

The bodies of the victims were found about 4 miles from where they were killed, just south of the city of Ensenada. A tent the men were staying in, as well as their burned-out truck, was found nearby.

María Elena Andrade Ramírez, chief state prosecutor of the state of Baja California, said investigators discovered their bodies 50 feet deep in a remote well.

Inside the well was a fourth cadaver as well, she said.

Three Mexicans are being held in connection with the case, the prosecutor said.

This gentrifying Mexico City neighborhood has a Soho House — and a migrant encampment

An encampment in the Juarez neighborhood of Mexico City shows how migration is impacting countries south of the U.S. border.

May 7, 2024

What does it mean for tourists?

The killings have set off pitched discussions over safety as well as the prioritization of solving the homicides of other tourists killed in Mexico.

On the Talk Baja Facebook group, concerned surfers and potential visitors to the Northern Mexico state have discussed whether they should still visit the area.

The U.S. State Department said in its 2023 report that Americans should “reconsider” travel to Baja California due to kidnapping and crime. The “reconsider” category is the second-worst category, after the department’s “do not travel to” recommendation.

More to Read

Testimony details alleged motives in Mexico surfer slayings: ‘Money, devices and the pickup’

May 9, 2024

Three friends drove from California to Mexico for a surfing trip. Then they disappeared

May 3, 2024

U.S. couple likely thrown overboard by boat hijackers are dead, Grenada police say

Feb. 27, 2024

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Noah Goldberg covers breaking news for the Los Angeles Times. He worked previously in New York City as the Brooklyn courts reporter for the New York Daily News, covering major criminal trials as well as working on enterprise stories. Before that, he was the criminal justice reporter for the Brooklyn Eagle.

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The Morning

When travel plans go awry.

There are ways of keeping ourselves anchored, even when we enter a parallel universe disconnected from time.

By Melissa Kirsch

The weekend trip is, in theory, the perfect break. Two nights someplace else, just a small duffel bag and limited logistics standing between you and a reset. Leave on Friday, come back Sunday, fill the hours in between with enough that’s novel and return refreshed, or at least with a slightly altered perspective. You might take a weekend trip for vacation or work or to see family, but the effect is the same. You’re a little changed on return. You see your regular life a little bit differently.

I took what was meant to be a quick trip last weekend to attend a college graduation, and it was, strictly speaking, quick: I was scarcely away for 48 hours, but extreme weather marooned me for most of those hours in the liminal spaces of transit — airports, grounded planes, traffic jams — where time loses legibility. An old friend used to call these neither-here-nor-there realms the “zero world” for the way they feel unfastened from reality, parallel to daily life but separate. The flight cabin after an announcement of a fourth lightning delay is a world detached from the one you know, a temporary society populated by temporary citizens with perhaps not much in common save one deeply held belief: We need to get out of here.

I was as cranky and impatient as the rest of my fellow travelers at each complication in our journeys, but also fascinated by the communities and customs and Cibo Express markets of the zero world. Each of us was, at any given time, one captain’s announcement away from a temper tantrum, but we were also competitively careful to be polite to one another and to the airline staff, as if determined to demonstrate that those wild videos of short-tempered passengers being duct-taped to their seats did not represent us, the makeshift civilization of this departure lounge.

Graduation, when I finally arrived, was a joyous affair despite the glitches. The speaker, an astronaut, showed a photo of the farm where she grew up, the place she thought of as home for much of her life. Then she showed a photo of the limb of the Earth, the glowing edge of the atmosphere, and described how, when she went to space, home was no longer a town on a map but this planet, a shift in perspective so massive I felt a little queasy contemplating it.

On Hour 3 in the airport bar on Sunday morning, beside two German travelers practicing Spanish, I ordered an omelet and imagined my own home, which felt very far away and lit by its own otherworldly halo. What would I be doing if I were there? Reading, texting, catching up on emails — the same things I was doing here. What was so bad about this? Was it the lack of choice? The lack of fresh air?

It was all those things, and also the feeling of being trapped in a warp between origin and destination. My emotions felt out of proportion to the situation: I hadn’t traveled very far for very long, was in no peril and would still arrive in New York with enough day left to do whatever needed to be done, but I felt on the verge of tears, loosed from my moorings, floating between fixed points, dislocated. I put on my headphones, put on a favorite band whose songs are so familiar they provide a home base no matter where I am. I listened to the same album on repeat for the duration of the flight, in the car on the way home, even at home once I finally made it there.

There’s a story in The Times today about how A.S.M.R., the pleasant, brain-tingling feeling we get when hearing certain sounds or watching certain comforting scenes, has become a feature of all viral internet content, not just specialized videos devoted to inducing the sensation. You can still put on a very specific video of someone whispering into a microphone or crinkling paper, but you’re just as likely to find the stimuli in videos of people cooking or cleaning their pools. This seems like a logical extension. We’re restless beasts in need of soothing. Sometimes we’re dramatically homesick, sometimes it’s just a bad day. Why not imbue the mundane with the choreography of comfort? Why not add pleasure whenever and wherever we can?

For weekend travel inspiration: The Times’s 36 Hours series.

How to deal with the increasing unpredictability of travel .

Stunning views of Earth from space .

How A.S.M.R. became a sensation.

THE WEEK IN CULTURE

The final round of the Eurovision Song Contest takes place in Sweden today. This year’s favorites include a Croatian techno act called Baby Lasagna. Read , or listen to , a guide to the competition.

“I won’t let anything break me”: Eden Golan, Israel’s 20-year-old entrant, spoke to The Times about the campaign to exclude her country from the event because of the war in Gaza.

The stage crew has 50 seconds to disassemble and reassemble sets. Watch a video from The Wall Street Journal .

Film and TV

“It’s easy to get caught up in the bigness of it all”: Owen Teague, the star of the latest “Planet of the Apes” film, and Andy Serkis, the lead in the earlier movies, sat down for a conversation .

“Kingdom of the Planet of the Apes” is not as transporting as the previous trilogy of films, the Times critic Alissa Wilkinson writes , but “there’s still a tremendous amount to mull over.”

The latest season of “Doctor Who,” starring Ncuti Gatwa as the 15th actor to play the doctor, opened with a double episode. Read a recap.

Disney and Warner Bros. Discovery announced a plan to bundle their Disney+, Hulu and Max streaming services this summer

The recording engineer Steve Albini, who died this week at 61, was “arguably the most influential figure ever to emerge from indie rock,” Pitchfork wrote . Listen to 10 of his essential tracks , which shaped the sound of alternative rock music.

Kendrick Lamar and Drake’s rap beef crashed the website Genius , where users can annotate lyrics to songs. Times critics discussed where the rappers’ sonic conflict goes next .

Other Big Stories

A stage version of the beloved animated film “Spirited Away” is running in London, after premiering in Japan. The adaptation is opulent and impressive, but it could use more heart , our critic writes.

A federal judge granted a preliminary injunction that would bar the Des Moines Art Center from dismantling “Greenwood Pond: Double Site,” an environmental work by Mary Miss that includes wooden walkways and sitting areas in need of repair.

The owners of the Los Angeles house where Marilyn Monroe last lived, and died, sued the city, accusing officials of “backroom machinations” to save it from a planned demolition .

David Shapiro, a lyrical poet who appeared in a famous photograph from the 1968 uprising at Columbia University, died at 77 .

THE LATEST NEWS

Israel-Hamas War

A Biden administration report said that Israel may have broken international law in Gaza, but that Israel’s “credible and reliable” assurances mean the U.S. can keep sending weapons.

The Biden administration is still waiting for Israel to show how it plans to evacuate and protect civilians in Rafah ahead of a possible invasion.

The U.N. General Assembly voted to support Palestinian statehood , a symbolic move. The U.S. voted no, and Israel accused delegates of “shredding the U.N. charter.”

Michael Cohen, who paid Stormy Daniels hush money and whom prosecutors say Donald Trump reimbursed, is expected to testify Monday in Trump’s Manhattan criminal trial. The judge asked prosecutors to stop Cohen from criticizing Trump .

Russia tried to break through Ukrainian lines in the country’s north using shelling and armored columns. Ukraine said it had repelled the attacks.

Russia is upgrading a munitions depot in Belarus, possibly to house nuclear weapons , a Times analysis of satellite imagery found.

The Biden administration plans to raise tariffs on Chinese electric vehicles to protect U.S. auto manufacturers.

Apple is revamping Siri to offer more advanced A.I. responses , akin to ChatGPT.

An appeals court upheld Steve Bannon’s conviction for defying a subpoena from the House Jan. 6 committee. He could soon have to serve prison time.

A Virginia school board voted to restore the names of Confederate leaders — including Robert E. Lee and Stonewall Jackson — to two schools, reversing its 2020 decision to rename them .

CULTURE CALENDAR

By Desiree Ibekwe

🎥 Back to Black (Friday): You may well have seen the online discussion about this movie, an Amy Winehouse biopic directed by Sam Taylor-Johnson. The movie — which focuses on Winehouse’s relationship with Blake Fielder-Civil — was No. 1 at the British box office but divided viewers and critics, some of whom found fault with the appearance of its star, Marisa Abela. “I don’t need to convince people that they’re actually watching Amy,” Abela told The Times . “I need to remind people of her soul.”

RECIPE OF THE WEEK

By Melissa Clark

Strawberry Shortcake

It’s Mother’s Day tomorrow, and if your mom has a sweet tooth (and if so, I can relate), Jane Grigson’s strawberry shortcake as adapted by Nancy Harmon Jenkins might be just the thing for a celebratory brunch. Make the biscuit dough and cut out the rounds the day before (just keep them in the fridge until baking time). Then, while they’re in the oven, you can macerate the berries (any kind you like) with sugar and prep the whipped cream. Be sure to save any leftover biscuits. They’re excellent toasted for breakfast the next day.

REAL ESTATE

The hunt: An American took a chance on the Lake Geneva area of Eastern France, with a $300,000 budget. Which home did she buy? Play our game .

What you get for $900,000: A Frank Lloyd Wright house in Wilmette, Ill.; an 1879 three-bedroom house in Wilmington, N.C.; or a renovated ranch house in Scottsdale, Ariz.

Free help: A filmmaker, feeling unhelpful in her daily life, decided to offer small favors to passers-by in Union Square.

Made for walking: Brides are increasingly pairing cowboy boots with relaxed silhouetted dresses.

Scarlett Johansson: The actress shared her beauty regimen with T Magazine.

How to: Restoring a chair is easier than one might think . Here’s how a couple known as the Brownstone Boys did it.

ADVICE FROM WIRECUTTER

Food processors, blenders and choppers.

Countertop appliances can help you get a meal on the table faster, often with less work and a quicker cleanup. But deciding which gizmo is best for you can be a challenge. It depends on what kinds of foods you most frequently prepare, Wirecutter’s kitchen experts say. For example, if your main goal is to reduce the time you spend prepping ingredients, a food processor is likely your best bet. If you demand the smoothest, silkiest textures from your soups, sauces and smoothies (and have ample storage space), consider a full-size blender. Oh, and those TikTok-famous manual vegetable choppers ? No one needs those. — Rose Lorre

GAMES OF THE WEEK

W.N.B.A. season openers: A once-in-a-generation group enters the W.N.B.A. next week. You may already know their names: Caitlin Clark, Angel Reese, Cameron Brink, Kamilla Cardoso. Their college matchups shattered viewership records, and their pro draft last month did the same. The W.N.B.A. is trying to seize the moment: Nearly all of Clark’s games with the Indiana Fever will be national broadcasts , and some of her games are moving to bigger arenas to meet fan demand.

The season begins Tuesday, as Clark and the Fever face the Connecticut Sun and M.V.P. contender Alyssa Thomas. After that, the two-time defending champion Las Vegas Aces play Brittney Griner and the Phoenix Mercury. 7:30 p.m. and 10 p.m. Eastern on ESPN2

More coverage

Clark and Cardoso are featured in a documentary series , “Full Court Press,” airing on ABC this weekend, which follows them through their final season of college.

The W.N.B.A. is expanding : The league plans to add a 13th team, in the San Francisco area, next season, and a 14th, in Toronto, the year after.

NOW TIME TO PLAY

Here is today’s Spelling Bee . Yesterday’s pangram was uncloak .

Take the news quiz to see how well you followed this week’s headlines.

And here are today’s Mini Crossword , Wordle , Sudoku , Connections and Strands .

Thanks for spending part of your weekend with The Times. — Melissa

Sign up here to get this newsletter in your inbox . Reach our team at [email protected] .

Melissa Kirsch is the deputy editor of Culture and Lifestyle at The Times and writes The Morning newsletter on Saturdays. More about Melissa Kirsch

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The huge solar storm is keeping power grid and satellite operators on edge

Geoff Brumfiel

Willem Marx

NASA's Solar Dynamics Observatory captured this image of solar flares early Saturday afternoon. The National Oceanic and Atmospheric Administration says there have been measurable effects and impacts from the geomagnetic storm. Solar Dynamics Observatory hide caption

NASA's Solar Dynamics Observatory captured this image of solar flares early Saturday afternoon. The National Oceanic and Atmospheric Administration says there have been measurable effects and impacts from the geomagnetic storm.

Planet Earth is getting rocked by the biggest solar storm in decades – and the potential effects have those people in charge of power grids, communications systems and satellites on edge.

The National Oceanic and Atmospheric Administration says there have been measurable effects and impacts from the geomagnetic storm that has been visible as aurora across vast swathes of the Northern Hemisphere. So far though, NOAA has seen no reports of major damage.

The Picture Show

Photos: see the northern lights from rare, solar storm.

There has been some degradation and loss to communication systems that rely on high-frequency radio waves, NOAA told NPR, as well as some preliminary indications of irregularities in power systems.

"Simply put, the power grid operators have been busy since yesterday working to keep proper, regulated current flowing without disruption," said Shawn Dahl, service coordinator for the Boulder, Co.-based Space Weather Prediction Center at NOAA.

NOAA Issues First Severe Geomagnetic Storm Watch Since 2005

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"Satellite operators are also busy monitoring spacecraft health due to the S1-S2 storm taking place along with the severe-extreme geomagnetic storm that continues even now," Dahl added, saying some GPS systems have struggled to lock locations and offered incorrect positions.

NOAA's GOES-16 satellite captured a flare erupting occurred around 2 p.m. EDT on May 9, 2024.

As NOAA had warned late Friday, the Earth has been experiencing a G5, or "Extreme," geomagnetic storm . It's the first G5 storm to hit the planet since 2003, when a similar event temporarily knocked out power in part of Sweden and damaged electrical transformers in South Africa.

The NOAA center predicted that this current storm could induce auroras visible as far south as Northern California and Alabama.

Extreme (G5) geomagnetic conditions have been observed! pic.twitter.com/qLsC8GbWus — NOAA Space Weather Prediction Center (@NWSSWPC) May 10, 2024

Around the world on social media, posters put up photos of bright auroras visible in Russia , Scandinavia , the United Kingdom and continental Europe . Some reported seeing the aurora as far south as Mallorca, Spain .

The source of the solar storm is a cluster of sunspots on the sun's surface that is 17 times the diameter of the Earth. The spots are filled with tangled magnetic fields that can act as slingshots, throwing huge quantities of charged particles towards our planet. These events, known as coronal mass ejections, become more common during the peak of the Sun's 11-year solar cycle.

A powerful solar storm is bringing northern lights to unusual places

Usually, they miss the Earth, but this time, NOAA says several have headed directly toward our planet, and the agency predicted that several waves of flares will continue to slam into the Earth over the next few days.

While the storm has proven to be large, predicting the effects from such incidents can be difficult, Dahl said.

Shocking problems

The most disruptive solar storm ever recorded came in 1859. Known as the "Carrington Event," it generated shimmering auroras that were visible as far south as Mexico and Hawaii. It also fried telegraph systems throughout Europe and North America.

Stronger activity on the sun could bring more displays of the northern lights in 2024

While this geomagnetic storm will not be as strong, the world has grown more reliant on electronics and electrical systems. Depending on the orientation of the storm's magnetic field, it could induce unexpected electrical currents in long-distance power lines — those currents could cause safety systems to flip, triggering temporary power outages in some areas.

my cat just experienced the aurora borealis, one of the world's most radiant natural phenomena... and she doesn't care pic.twitter.com/Ee74FpWHFm — PJ (@kickthepj) May 10, 2024

The storm is also likely to disrupt the ionosphere, a section of Earth's atmosphere filled with charged particles. Some long-distance radio transmissions use the ionosphere to "bounce" signals around the globe, and those signals will likely be disrupted. The particles may also refract and otherwise scramble signals from the global positioning system, according to Rob Steenburgh, a space scientist with NOAA. Those effects can linger for a few days after the storm.

Like Dahl, Steenburgh said it's unclear just how bad the disruptions will be. While we are more dependent than ever on GPS, there are also more satellites in orbit. Moreover, the anomalies from the storm are constantly shifting through the ionosphere like ripples in a pool. "Outages, with any luck, should not be prolonged," Steenburgh said.

What Causes The Northern Lights? Scientists Finally Know For Sure

The radiation from the storm could have other undesirable effects. At high altitudes, it could damage satellites, while at low altitudes, it's likely to increase atmospheric drag, causing some satellites to sink toward the Earth.

The changes to orbits wreak havoc, warns Tuija Pulkkinen, chair of the department of climate and space sciences at the University of Michigan. Since the last solar maximum, companies such as SpaceX have launched thousands of satellites into low Earth orbit. Those satellites will now see their orbits unexpectedly changed.

"There's a lot of companies that haven't seen these kind of space weather effects before," she says.

The International Space Station lies within Earth's magnetosphere, so its astronauts should be mostly protected, Steenburgh says.

In a statement, NASA said that astronauts would not take additional measures to protect themselves. "NASA completed a thorough analysis of recent space weather activity and determined it posed no risk to the crew aboard the International Space Station and no additional precautionary measures are needed," the agency said late Friday.

People visit St Mary's lighthouse in Whitley Bay to see the aurora borealis on Friday in Whitley Bay, England. Ian Forsyth/Getty Images hide caption

People visit St Mary's lighthouse in Whitley Bay to see the aurora borealis on Friday in Whitley Bay, England.

While this storm will undoubtedly keep satellite operators and utilities busy over the next few days, individuals don't really need to do much to get ready.

"As far as what the general public should be doing, hopefully they're not having to do anything," Dahl said. "Weather permitting, they may be visible again tonight." He advised that the largest problem could be a brief blackout, so keeping some flashlights and a radio handy might prove helpful.

I took these photos near Ranfurly in Central Otago, New Zealand. Anyone can use them please spread far and wide. :-) https://t.co/NUWpLiqY2S — Dr Andrew Dickson reform/ACC (@AndrewDickson13) May 10, 2024

And don't forget to go outside and look up, adds Steenburgh. This event's aurora is visible much further south than usual.

A faint aurora can be detected by a modern cell phone camera, he adds, so even if you can't see it with your eyes, try taking a photo of the sky.

The aurora "is really the gift from space weather," he says.

• space weather
• solar flares
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