What Causes a Circuit Breaker to Go Bad?

Switching does not cause early wear of circuit breakers; rather, it is more common for a circuit breaker to be used less than 100 times during its life cycle, much less than the regulatory requirements. In most cases, these failures are caused due to overheating resulting from moisture or the circuit breakers being used to protect faulty circuits from the beginning of their installation.

According to my experience, six mechanisms are involved in nearly all failures of circuit breakers as seen in service reports. Out of these six mechanisms, five can be seen before a failure occurs.

The simple response to this inquiry would involve the heat built up at a bad connection and later regular working of the device, humidity, and corrosion problems, problems with device quality, such as federal pacific Stab Lok and Zinsco systems, incorrect device usage based on load as well as voltage spike much worse than damage from other things happening inside GFCI and AFCI devices. Most of the time the device acts as the messenger, but the true cause usually involves issues with connections, location, or circuit.

The Five Failure Mechanisms, in Order of Frequency

• Loose Terminals. An inadequately torqued screw increases resistance, making the joint become increasingly hot, thereby transferring excess heat to the body of the breaker.
• Continuous Tripping. Each trip creates stress on the mechanism and contacts. Circuits that trip more than once a week dramatically reduce the operational lifespan of the breaker.
• Moisture and Corrosion. Moisture in the basement, yard, or garage can lead to corrosion of the bus and contacts.
• Wrong or Fake Product. Wrong curve, wrong interrupting capacity, or a fake breaker that has not adhered to the standards.
• Surges and Anomalies. These rarely harm thermal-magnetic breakers; however, they destroy the electronics in GFCI, AFCI, or “smart” devices.
• The sixth cause is really not a problem of the mechanism but rather of a legacy, because some panel designs created between the 1960s and the 1980s are known to mal-function.

Loose Terminations: The Number One Cause

Copper moves . Aluminium moves even more. A connection tightened to the recommended torque value at the time of installation may loosen after twenty years of heat cycling, and this will lead to an increase in temperature of the connection itself, which will cause further loosening and even more heating of the joint.

Failure happens gradually and is not easily noticed from a glance at the back of the panel. So what you see at the end is insulation material with discoloration along with terminal lugs and a breaker with a “softened” housing. In other words, what you can’t see up until the point when it starts arcing is the inside of the connection joint.

There are two ways to prevent the problem. First, torque to the value written on the equipment or the panel label, not “firm,” and second, re-torque whenever any servicing is performed because a twenty-year serviceable panel will have different terminations from the original ones. A thermal imaging survey identifies hot spots in a pane and it takes around one minute to conduct the survey for one panel. That is the service our technical team performs before recommending any replacement.

Aluminium conductors should be given a separate notice. It is important to have a device which is specified for aluminium conductors, as well as an antioxidant material required by the manufacturer and a torque wrench instead of a screwdriver. If a breaker rated for copper is attached to an aluminium feeder, problems are likely to arise once there is a load on the circuit.

Repeated Tripping and Thermal Cycling

This is why after years of nuisance tripping, a breaker may have the opposite effect of working better over time. It is also why simply “resetting it” is not the proper course of action, if a circuit trips regularly.A standard thermal-magnetic device, such as this single-pole 32 to 63 A MCB, is built for thousands of operations, but not for thousands of fault interruptions.

Moisture, Corrosion and Dirty Panels

There is a clear connection between water and electricity, but the process of failure here is more gradual and less spectacular compared to that of other methods. Humidity condenses on cold busbars, and that condensation forms a film containing dirt and salts which has a little bit of conductivity. The first sign of failure is nuisance tripping during seasons of high humidity, while the second is the corrosion (at the point of contact) that leads to an increase of resistance and starts the heat cycle described above in this paper.

Typical cases of this type occur with panels situated in garages, outbuildings, basement and outdoors, and the solution to the problem is proper enclosure with the suitable IP rating instead of just covering the panel with plastic sheet.A watertight board rated for dusty and wet locations, such as this IP65 modular distribution board, keeps the condensation cycle on the outside where it belongs.

One particular risk: a panel that has been submerged, even if just for some time, should be replaced instead of dried. Water will get to the internal clearance of every device, and the residue left is conductive.

Wrong Device for the Load

There are three variants of this error that are commonly made in practice.

• The wrong trip characteristic: A B-curve device used in a motor circuit trips at every start. The proper solution would have been to replace it with the appropriate device. However, instead of replacing it properly, someone installs a device with a higher rating. Therefore, the cable is unprotected, while the motor is still tripping – although now it is doing this a little later.
• The wrong interrupting rating: In situations where the available fault current is around 10 kA, a device rated for 3 kA will not effectively interrupt a short circuit. Unfortunately, it may be quite difficult to identify that something is wrong before it is too late.Devices designed for residential and light commercial boards carry ratings of 6 to 10 kA for exactly this reason, and the difference is visible in the specification of this 10 kA single-pole miniature circuit breaker.
• The counterfeit or incompatible device: A breaker produced by another manufacturer may fit into the bus properly, but that does not mean it can replace the original device. The geometry of the connector and the bus contact are part of the design approved in the certification process. If an improperly fitting device is installed, the bus contact will get too hot.

Manufacturing-Era Defects

The two panel brands of the middle of the 20th century have a known record of failure that cannot be solved by simply swapping breakers: Stab-Lok by Federal Pacific and Zinsco. Both brands have been associated with devices that have failed to trip in case of fault, which has led to an increase in litigation and regulation.

When it comes to any panel bearing either brand name, it would be best to have it checked by a licensed electrician and replaced instead of replacing just the faulty breaker. The same goes for Pushmatic panel breakers, which have been outdated altogether and which work with an unfamiliar bus design, which makes them some of the least used breaker boards by modern electricians.

Identifying a panel involves more than just identifying a breaker. The printing conventions are different enough that sometimes it becomes more convenient to attach a photo of the name of the panel.

Voltage Transients

A lightning strike or event of switching utility creates pulses of several microseconds and several kilovolts. Thermal and magnetic breakers are incapable of functioning during the microsecond pulses as they take far too short time to heat up the bimetallic strip. However, the pulse destroys insulation of the winding of the motor and control boards and even destroys the electronic components of the GFCI, AFCI, or smart breaker.

That is why sometimes a house can have functioning circuit breakers and yet have three completely ruined GFCIs after a storm.The protection that prevents it is a surge protective device at the panel, sized to the exposure: a Type 1+2 SPD with a 50 kA maximum discharge current for a service with overhead supply, a smaller Type 2 device for a buried service in a low-lightning area.

What Actually Prevents It

• Tightening all terminations to the required torque value, and then tighten the panel again if any work is required on the panel.
• Repairing a trip circuit instead of resetting it once every week.
• Providing suitable enclosure to keep the water out and replacing a panel if it is dampened.
• Selecting an efficiently designed panel for the specific device to be used and matching it for the cable current rating, fault rating and load characteristics.
• Installing a Type 2 SPD at the panel and a Type 3 protection at any sensitive equipment connected to the panel.
• Getting a thermal survey done on the panel at intervals to look out for hot joints forming.

FAQ

How do you know when a circuit breaker needs to be replaced?

The circuit breaker is not resetting itself, is tripping while it was unloaded or is getting hot and smells burnt. While old age is a reason to examine a breaker, it is not necessarily the reason to change it.

What is the most common cause of circuit breaker failure?

The weakening joint leading to heat build-up in an electrical component. In general, the device has suffered failure due to being improperly tightened at the moment of installation.

How common is it for a circuit breaker to go bad?

Circuit breakers are not so much common as they are the kind of thing that every electrician has to carry replacements for—but they are really rare relative to their numbers in service. Most circuit breakers go on for decades without any problems.

What is the average lifespan of a circuit breaker?

For regular thermal-magnetic circuit breakers, it is about 25 to 30 years. GFI and AFCI devices, however, tend to fail significantly sooner because of their electronics and technology.

References

• NEMA — Circuit Breaker Application and Installation Guidance
• UL Solutions — Circuit Breakers, Molded Case and Low Voltage
• U.S. Department of Energy — Residential Electrical Safety
• This Old House — Electrical Panel Repairs and Upgrades
• Bob Vila — Why Breakers Fail

Conclusion

A circuit breaker could malfunction in different ways. It can break down due to high heat, moisture, or flawed connectors. However, only one type of breakdown can happen inside the apparatus, while the other two are happening outside it, at the panel. Therefore, replacing the breakers but not repairing the junction is a costly mistake that is often made in the industry.

If a panel keeps tripping, provide us with its nameplate, circuit information, and bus picture.