How To Tell If A Circuit Breaker Is Bad (And The Next Steps To Take)

Circuit breakers, despite any techy magic happening beneath the surface, should be the most predictable things in the world. If they encounter a ground fault or an overcurrent/overload situation (or some types of electrical arcing, depending on the breaker), they should shut down the circuit. No drama, other than figuring out what to do with the stuff in your stalled bread machine. There should be no buzzing, no burning smells, no scorching or sparking, no hot circuit breakers or inexplicable flickering of lights.

Bad circuit breakers are uncommon, but uncommon things happen all the time. Breakers that are defective from the manufacturer are exceedingly rare, and a quality breaker can last over 40 years. But an expected lifespan means something happens at the end of that lifespan: the circuit breaker no longer does its job.

If experience any of the signs above, you're past the point of much diagnosis. Turn off the breaker. If that doesn't stop the sparks or buzzing, turn off the power to the entire house and call an electrician. But there are subtler signs that might prompt you to do a little investigation before investing in that electrician's new Maserati. If you experience frequent tripping that seems unwarranted by a circuit's load, the breaker is a sensible thing to check. It's also a good idea if your breakers are quite old (say, older than 30 years), have signs of physical damage like cracked cases or visible corrosion, if your power fluctuates for no apparent reason, or if a breaker simply doesn't act like you expect it to act. Again, these should be the most predictable devices in your house.

The most common scenario that might cause you to doubt your circuit breakers is when a breaker won't properly reset, or won't stay on for long after you reset it. The most likely explanation is that there's something on the circuit causing a problem — possibly that thrift store bread machine — but you have one thing to check before you start defaming the bread maker. Be sure that you're properly resetting the breaker. Most tripped circuit breakers require that you fully flip them to the "off" position, then to the "on" position in order to reset them. If you skip the "off" step, it might seem as if the breaker won't reset at all.

If that doesn't work, your next step is to be sure you've identified the right breaker for the circuit in question (or the right circuit for the breaker in question), then flip that breaker to the "off' position. Now, unplug everything that might be on or near that circuit, and turn off every light, ceiling fan, or anything else you can't unplug. If you then reset the breaker and it trips again or won't reset at all, checking for a fault breaker is a good bet. 

Keep in mind that there could be other causes, like wiring issues or problems with your breaker panel itself. A similar problem is when a reset breaker doesn't seem to be allowing power through to the circuit. If you have and know how to use a multimeter, you can test for voltage on the reset breaker.

The opposite circumstance — a breaker that stays energized even though it's tripped or doesn't seem to trip when it should — is a less likely, but more alarming scenario. In such a situation, it would be completely reasonable to shut down power to the house and call an electrician for emergency help. Your course of action might depend on why you're suspicious of the breaker. If you have two space heaters or a couple of big electric fans on a single 15-amp circuit, you might expect it to trip the breaker, and blame the breaker if it doesn't comply. Perhaps the most likely explanation, though, lies in the complex calculations some circuit breakers use in deciding when to trip.

Some breakers are designed to delay tripping based on how overloaded the circuit is, tripping sooner for big overloads and later for smaller overloads. This is called inverse time tripping, and it prevents constant "nuisance tripping" when a problem is quickly eliminated or when a transient overload is caused by a common situation like an electric motor that demands excess power, but only when it first starts up. So if you accidentally overload a circuit but the breaker doesn't trip, this might be all that's happening. You can test it by introducing a load that's more than 200% of the rated ampacity of the breaker and leaving it on for a bit; modern breakers should trip at this threshold. But it might be more sensible to call an electrician than to intentionally overload your circuits when you already suspect a wiring or breaker problem.

Arc-fault circuit interrupt (AFCI) breakers, ground-fault circuit interrupt (GFCI) breakers, and variations of them (CAFCI, AFI, GFI, dual-function, etc.) have a "test" button just like their wall-receptacle brethren. These breakers do more than standard circuit breakers that only monitor the load and ampacity of a circuit, and you can test that additional functionality with — you guessed it — the "test" button. Just press the button while the circuit is in operation, which should trip the breaker. If it doesn't, the breaker should be replaced. Note that the "test" button only tests the AFCI and/or GFCI functionality of the breaker. You should still test a suspect AFCI or GFCI breaker using the standard methods described above.

Some breakers, like Schneider Electric's Homeline QO, QOB, and HOM AFCI and dual-function models, have additional diagnostic indications built into this testing function. The Schneider Electric process works like this: remove all loads from the circuit, turn the breaker off, then hold down the test button while turning the breaker back on and waiting at least five seconds. The amount of time one of these breakers takes to trip after the test procedure indicates if there's a problem with the breaker. The amount of time the trip takes (less than one second, two seconds, or five seconds) indicates the type of fault the breaker experienced. This can be useful in diagnosing faults in the circuit, thereby eliminating suspicions about the breaker itself. Smart and connected circuit breakers also sometimes include this kind of diagnostic information, and might require additional hardware for testing.