Quote:
Originally Posted by SAABDOCTOR
I use a circut breaker in place of the fuse. I am cheap!:d
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I know that we all have breakers somewhere....in our house electrical panel, in the RV or motorhome, boats, etc....you name it, breakers a more common than fuses. So, having said that, one of the issues with using breakers is....when should I replace a breaker? Molded case breakers generally operate with two types of trips....thermal and magnetic. A thermal trip is associated with a current overload.... i.e. your 15A breaker has a 17A load places on it. Depending on the trip curve that the breaker has been designed with, XX amount of time will elapse before the breaker trips out and opens the circuit. Everyone resets the breaker and gives it another try. If the overload condition is still present, the breaker will trip again. Now, the magnetic trip part of the breaker.....This magnetic trip (M.T.) is the part of the breaker that trips when it senses a fault condition....a direct short or ground of the item that is being fed. Generally speaking, a breaker can be reset after a thermal trip, but it is pretty sketchy to keep using a breaker that has been through a magnetic trip or fault. So....how do you know which happened? The short answer is...you dont!....unless you reset it and try again. If there is some time between reset and trip (let's say a few to several seconds....maybe a minute), you most likely are experiencing an overload. Instantaneous tripping after reset is most likely a ground or short between the pos. and neg. or in an Alternating current situation...phase to neutral or ground. If you experience an instant trip (think magnetic and shorted or ground circuit) you should replace the breaker as you have no idea how much current has passed through the breaker and if it is capable of protecting the circuit in the event of another fault. And before anyone says.....oh, it's just a little 120VAC circuit, be aware that depending on the KVA rating of the supply source and the impedance of the transformer that supplies that source, you can have 10's of thousands of AMPS available fault current......Nope, that's NOT a typo......10's of thousands of Amps.
So, resetting a breaker can be a risky proposition if it has been through a short circuit type fault or a phase to ground type fault. A mild overload trip isn't nearly as risky.........but do you know for sure which one happened?