testing circuit breakers


Old 04-20-07, 05:21 PM
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Join Date: Dec 2006
Location: orange county
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Question testing circuit breakers

Have three theoretical questions. Question # 1 How long does it take for a c/b to open once it exceeds it's rating. #2 How can one be assured that one's c/b will open when the current exceeds its design rating? #3 is there a safe way to test (load up ?) a circuit to test to see if it truly is going to open when it is supposed to? In the HVAC industry, if I want to see if the limit t-stat on a furnace is operating properly I merely disconnect the fan and wait. With my trusty thermometer in the plenum I can easily see at what temp it opens. Very re-assuring. Thanx in advance for your time ,as always
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Old 04-20-07, 06:16 PM
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How long it takes for the breaker to open would depend on whether it was a dead short where it would open instantaneously, or an overload where it could take quite a bit longer.

As for whether or not is would work as designed I believe that you would have to rely on the factory to turn out a good product that mets the UL specs.

There are load banks available to impose a load on the circuit or you could add a high load by adding high draw appliances to the circuit and time how long it takes.
Old 04-20-07, 06:17 PM
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1. Circuit breakers used in home wiring typically have two different methods for tripping. In the event of a high current short (such as hot shorted to ground or neutral) they trip very quickly. In the event of a low current trip, such as something close to their limit, they trip slower. This is to allow motors time to start, and get the high current they need to start. The high current is tolerated for a short period of time, but if it continues the breaker will trip. I do not know the times.

2. You can't.

3. No. Do not intentionally cause short circuit or an overload to test a breaker.
Old 04-21-07, 03:32 AM
Join Date: Apr 2006
Location: New Bern, NC
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There was a person posting on the forums last year claiming to be developing a tester for field testing circuit breakers. I have not heard of any such device being approved.

Unless this guys product went through, there are NO testers available to field test circuit breakers. All breaker testing must be done in a testing labratory, like UL.

Trip curve charts are available for all circuit breakers from the mfg. They show the inverse time characteristics of the breaker. The higher the amperage the faster they trip.
Old 04-21-07, 08:29 AM
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Location: orange county
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Thank you Pcboss, Raycraft, and Jwhite for your responses. Have a great week-end.

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