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I have an external cutoff for my air conditioner that has two physical fuses (TR-50's, time delay 50 amps) outside. This is between the condenser unit and the main power panel, where it is protected by a 50 amp circuit breaker.

An electrician is coming to replace the cutoff (containing fuses) with a simple lever cutoff.

In discussing this he said that a circuit breaker should not be allowed to trip more than 4 or 5 times before being replaced.

That struck me as odd. I have never experienced a need to replace a breaker, and some in my house due to stupid wiring patterns (a plug we use for a kettle is on the same circuit as the plug my wife uses for her hair dryer in the washroom) have tripped more often than 5 times.

I am trying to decide if he trying to upsell me, or has a valid point.

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Curious. Even though Google finds plenty of claims that breakers can survive up to 2-3 faults I've never in my whole life heard anything like that from local maintenance people and as you might guess they are eager to upsell just about anything so they'd be the first people to tell me that. –  sharptooth Jul 2 '12 at 9:50
I wonder if this was ever true, maybe this was some FUD that started circulating when breakers started replacing fuses? Perhaps you should give the folks over at skeptics.stackexchange.com a crack at this mystery. –  auujay Jul 2 '12 at 14:38
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5 Answers

up vote 6 down vote accepted

Breakers do wear out, and do fail, but without looking it up i would say that wear is not an issue until hundreds or thousands of trips. When they fail, they almost always fail open anyway. I have seen dozens of failed breakers, and they always fail open. Each breaker is tested several times at the factory, and one that has tripped few times in the field is probably more reliable since this type of device has higher failure rate at the beginning and end of life, with most reliable service after some use. Lifetime is not determined just by number of trips, but by how hot it gets for extended periods and, of course, it is working hardest just before it trips so if the circuit is overloaded but rarely trips the breaker is working harder than one that trips regularly due to short overloads.The former sounds like your situation so i would replace just to avoid nuisance trips in the future. Breakers are cheap.

Also, very old breakers have less stringent standards than new ones, depending on national electrical codes so for very old breakers it is always a good idea to upgrade when doing a major rewire.

Finally, when breakers do start to fail they often start to become too sensitive and trip at lower than rated current so if it trips a few times even though it looks like circuit is not overloaded its a good idea to change the breaker.

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I've sold breakers for 25 years and never heard of it, but it doesn't make it untrue. Weigh the difference in the price he is charging you to put the breaker in now against what it would cost to have him come back and change it. Then compare your savings. No savings means don't do it until you start having problems.

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I don't know. But I've had two breakers fail, both of which had tripped many times (including an exciting "fail closed"--luckily while I was standing there with the breaker box open and could pull the master switch).

It may have depended on the build quality of the breakers, or there may have been other problems. The wiring in that house was quite dodgy.

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I find this hard to believe, but it may be true in the "worst case" of a dead short.

A breaker has an electromagnet in it, that when a certain amount of current is passing through, causes the spring-loaded contacts to release. Therefore, best case, it should last as long as a relay -- it is an anti-relay, in a sense.

Now if you have a hard short, that may stress the electromagnet for the 200 milliseconds or so it is absorbing the extra current, and that may reduce its lifetime. Breaking a high-current load may also pit and burn the breaker's contacts.

Contrast this with plugging in one too many appliances, where the electromagnet is operating well within design parameters -- it should last nearly as long as an ordinary wall switch in this case.

I think he's trying to up-sell you. Contact the manufacturer of your circuit breakers for the definitive info, and if they don't back the electrician up, report him to your local better business bureau.

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Circuit breakers are more often than not certified to open a fault at its maximum rating (AIC) exactly once in its lifetime, at which time it is recommended to be returned to the manufacturer for recalibration and testing. That said breakers frequently can open large faults more than once, however manufacturers are not required to guarantee this.

Often a breaker that has tripped multiple times does so under an overload (not short circuit or ground fault) condition. If this happens several times in a short duration, such as a matter of hours, the temperature of the internal components can become very high. If you've ever had experience with a breaker which under excessive load trips after a few minutes, is reset immediately and placed under the same load trips within maybe a minute, then seconds, and then possibly will not reset at all until a period of time has passed, then you may have noticed that such a breaker will permanently become more prone to trip. From my experience this is the most common cause of a "weak" breaker. Less often a breaker will be closed into a bolted or arcing fault condition repeatedly, which can lead to internal contacts actually blowing apart or possibly even welding; once again this sort of use goes far beyond what a manufacturer is going to stand behind as accepted use and can actually lead to dangerous and catastrophic failure of a breaker when it can no longer contain the arcing happening within causing it to completely destroy its internal mechanisms or even rupture its outer casing.

The subject gets more complicated when factors such as HACR, SWD, HID and other specialized ratings of breakers are taken into account as all these classes are made to withstand higher than normal temperature and operating conditions. In the case of refrigeration equipment such as an air conditioner a HACR rated breaker is required, it can take the high inrush conditions of starting such a load without damage over time. Nearly all (probably all) currently produced breakers are HACR rated. With circuit breakers you pretty much get what you pay for and a more expensive breaker is more likely to operate better for a longer period of time than the cheapest thing on the shelf.

Finally there is the possible situation of older breakers in a situation where the utility serving said breakers has upgraded its own distribution systems, leading to higher available fault current than may have existed when the original installation was done. Say a thirty or forty year old breaker panel was installed on a system where no more than a 5K amp interrupting current, or AIC rating was required due to line lengths, inefficient transformers or many other factors. Decades later the utility grew sick of their inefficient distribution transformers wasting electricity and upgraded their system. This is all well and good except with this they now require a 22K AIC rating on any new systems. That 22K refers to 22000, yes thousand, amps available under a worst case bolted fault condition. This is a big difference from the 5000 amps those thirty year old breakers were designed to survive and can once again lead to catastrophic failure, ie explosion. Utilities aren't required to make sure their customers existing distribution systems can survive an upgrade in fault current availability, so if you have fairly old breakers it might be wise from a safety standpoint to have a knowledgeable person survey your electrical system and identify any possible risks such as these.

The bottom line is if you think something might pose a problem when it comes to electrical equipment like breakers the best thing to do is have it checked out by someone with training and experience in the field, your electrician should be obviously fairly knowledgeable on the subject and it is often a good idea to weight their opinions higher than say the guy at a hardware store or even a maintenance person who doesn't have considerable experience or training in all things electrical.

Sorry for the long winded response however as many things electrical go there are often few simple, general answers to anything. When in doubt, call an electrician, and if you suspect the answer you get, call a different one. Leave it to the pros!

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