Trippin’  How many times can a breaker trip? Inquiring minds want to know. Wenatchee Home and Real Estate Inspection services.

This came up on a recent Home Inspector’s board and thought it was an interesting subject. (Thank you Mr. Egan for sending me down the path ; )

So, how many times can a circuit breaker trip? I really did not know what the correct answer was. So I did a little research and found the the answer is “it depends”.

For MCB (Miniature Circuit Breaker), which what we find in most homes they have to meet a criteria set by UL Standard 489 and NEMA Standard AB1 for Molded Case Circuit Breakers (MCCB).ETA White Paper

With 100 amp or less breakers they are tested to be operated 6000 times at rated current and 4000 without current, that is 10,000 operations, most likely they will never see that many operation unless the breaker is being used as a switch and in the right scenario, so highly unlikely this will be exceeded.

But now we move into two other criteria- Overload and Short Circuit.

In an overload condition they are rated for 50 operations at 6x (600%) rated current. During UL 489 testing, the device must survive short-circuit testing and continue to provide future overload protection.

From Eaton (Cutler Hammer) literature: UL489,(document link) requires that a breaker must safely clear its maximum current, which is the short circuit current rating of the breaker, twice and still be functional.  Schneider  (Square-D) uses this same criteria (document link).  And per IEEE 3.35 Circuit breaker useful life: it is prudent to replace any MCCB that has interrupted, at most, two faults at rated maximum current.

But wait, Eaton later in the document goes on to state-

“In actual application, high fault levels are extremely rare (less than 2% of all faults). An arcing fault is by far the most common type of a fault and the only type of a fault that can occur after installation. Arcing faults are usually the result of an insulation failure within a motor or wiring system. Such faults are initially very low level faults that if not cleared quickly can escalate rapidly. Arcing faults can also occur as the result of accidental contact between exposed live conductors, such as the dropping of a tool across exposed terminals. Molded case circuit breakers have dead front construction with no exposed live parts to help prevent such “accidental contact” faults. Molded case circuit breakers can be expected to safely clear such faults many times and still be operable.”

If it a maximum rated short has caused the breaker to trip more than once it is most likely time to replace the breaker.

Knowing what caused the breaker to trip either by overload (which is usually thermal trip) or short circuit (usually magnetic trip) will determine if the breaker needs to be replaced. This means that a qualified electrician should evaluate the cause and perform repairs and replacement as necessary.

So this also brings into the question of the not so uncommon practice by some electricians of intentionally shorting the circuit to determine what breaker is protecting the branch circuit. Should they replace the breaker now?

“If you think it's expensive to hire a professional to do the job, wait until you hire an amateur.”

Red Adair

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