What Do Tripped Circuit Breakers and Blown Fuses Indicate?

The purpose of both devices is to interrupt a circuit before another malfunction happens. A trip or a blown fuse are both pieces of information and not just a hassle; at this point, the artefact has not caused any trouble.

Properly interpreting the message will lead to getting fixed in five minutes or needing the repairman back every another fortnight.

The main takeaway: A circuit breaker that trips or a fuse that blows indicates that there was too much current flowing through the circuit. In addition to that, both the time taken for this to happen and its pattern help in identifying whether it was an overload, a short circuit, a ground fault, or an arc fault. An overload develops gradually and results in a trip after the circuit has been used for a while. In the case of a short circuit, an instantaneous trip occurs, which is usually accompanied by a bang. A ground fault also results in an instantaneous trip, which is usually caused by an appliance that operates when it’s wet or by a broken wire. An arc fault, however, results in an occasional trip and doesn’t usually affect the workings of other circuits in the area.

The Four Messages

Timing is a key indicator. An overload takes time to warm up the bimetal, so it does not trip at once after it is switched on. A short circuit, on the other hand, is instant. If you turn on a breaker and it opens despite the fact that nothing is switched on, there is a wiring fault, and it will not change, no matter how many times you reset the breaker.

The overload scenario is probably the most common and the least understood. A 15 A circuit feeding a load of 1,800 W for lighting, 1,500 W for a heater and 900 W for a kettle is performing exactly as required by the laws of science. The devices that make up an ordinary overload are described in this single-pole MCB specification, and nothing in it will help a circuit that is genuinely carrying too much.

What a Breaker and a Fuse Each Tell You

Both types of devices are capable of interrupting an undesirable overcurrent but they do so in different ways.

When a fuse blows, it uses the calibrated link to blow out. It reacts instantly to very large current faults and operates in current-limiting mode, meaning that it opens its contacts before the fault current reaches its peak value. That is the reason fuses are still more effective at protecting semiconductor and certain motor circuits than circuit breakers. When a fuse fails, you just replace it regardless of the extent of the damage, whether the fuse just blew out (in which case the body will be black and damaged) versus “hard” failure (in this case the element will stretch itself and break off).

As for the circuit breaker, rather than blowing out, it is shutting the fault current off by interrupting an arc in the current conducting part of the device. The advantage of the circuit breaker is that it can be reset. The interrupting process itself is covered in our guide to 10 kA miniature circuit breakers, where the breaking capacity is the number that decides what the device can safely interrupt.

One meaningful difference: a fuse that has blown cannot be tested. Also, any cartridge type fuse has to be replaced by the same type and specification. If a 20 A fuse was used instead of a 13 A one in a plug or, in general, a feed, then the situation would be dangerous, just like using a bigger protective device.

Why a Tripped Breaker Is Not Always the Breaker’s Fault

There are three instances of repeated tripping that have nothing to do with the device.

• A shared neutral. In a multi-wire branch circuit, two circuits share a neutral. If the neutral is disconnected, the voltages vary in each of the two circuits, resulting in trips of the devices used in both circuits and potentially damaging the electronic components. This is a fault in wiring, and the result can be mistaken for the breaker malfunctioning over a long period.
• An appliance creating trouble. A washing machine that has a leaking pump seal, a refrigerator that has compressor trouble, or a kettle having a wet element. The circuit itself works properly until the faulty device is applied. Hence, this is why the appearance of trips seems random.
• One leg fault. When a double pole device trips two legs at once, even if only one leg is faulty, it makes a device appear as if it has just failed rather than being broken.The construction behind that behaviour, and why common trip matters, is described in this two-pole miniature circuit breaker.

One leg fault. When a double pole device trips two legs at once, even if only one leg is faulty, it makes a device appear as if it has just failed rather than being broken.

Is It Safe to Reset?

Once, perhaps. However, repeatedly, it would not be advisable.

Resetting a circuit breaker with a continuing fault is not hazardous by itself because the equipment is designed to do so. However, there is the issue of damage occurring as a result of a reset, since each time a breaker is reset it causes arcing across the electrical contacts of the breaker, leading to wear and tear on the equipment. While it may be able to withstand hundreds of resets without an issue, whenever the fault is persistent, the breaker may trip at the wrong level of current due to the excessive number of resets.

In addition, whatever gets damaged downstream of the fault, is more than likely to incur damage during a subsequent fault condition. A short circuit of several hundred amps to compressors, control boards or motor windings does not benefit from repetition, and equipment that could have been saved after the first fault is usually replaced after the tenth.

The rule to follow is that you should reset a breaker once, and write down what happened. If the breaker trips again, stop and check what is wrong. The procedure for that diagnosis is in our breaker and panel FAQ.

Will a Blown Fuse or a Tripped Breaker Start a Fire?

The answer is no. The purpose of both types of device is to protect from situations where those very practices apply.

It is human behaviour that creates the potential fire hazard – replacing a fuse with a higher-rated one, wrapping a fuse with foil or wire, installing a larger circuit breaker, or keeping a circuit breaker on. Any action taken in this regard would negate the protection provided by the device and would thus turn a malfunction into a source of heat in walls.

The second risk is the risk posed by an old device that does not trip anymore, which is very hard to detect. A panel built in the 1970s with original devices can be providing less protection than one would expect based on their markings, which means that testing is the only way to know how good the devices are. Our panel test and survey service exists because a breaker that fails to trip gives no warning at all.

FAQ

What is the most common cause of a tripped breaker?

Overheating can happen as a result of appliances using an overload that was never intended for device use. There are a lot of trips during winter and morning because of such items as a heater, electric kettle, or hair dryer using a general purpose power line.

How many times can a breaker trip before it goes bad?

Although hundreds of operations may qualify as acceptable under standards testing performed thousands of times, the actual limitation is neither the number of operations, as such, but rather the situation whereby a machine fails due to tripping at a lower current.

Is it safe to turn on a tripped breaker?

Yes, in case of no any odour of burning and no visible damage. In case it trips right after, stop as the circuit has a fault.

Will a blown fuse start a fire?

A correctly rated fuse will not. Replacing a fuse with one of a higher rating, or bypassing it with a wire, will remove the protective element of the fuse and allow faults to heat up the wires until they catch fire.

References

• NEMA — Overcurrent Protective Devices and Coordination
• UL Solutions — Fuse and Circuit Breaker Standards
• U.S. Department of Energy — Home Electrical Safety
• This Old House — Tripped Breakers and Blown Fuses
• Bob Vila — What Your Breaker Panel Is Telling You

Conclusion

A trip conveys a signal about the current it carries, and the timing tells you what kind it is. Slow implies overload, instantaneous indicates a fault, while intermittent represents a connection. A trip itself does not usually provide useful information.

If a trip occurs again after a proper reset, it means that the circuit needs to be checked and not simply replaced, though our company is ready to provide you with either one.