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flyrod 12-29-2005 08:49 PM

delayed breaker trip
 
Replaced a breaker today on the garage circuit of a ten year old rental home. As far as I know, it powers the overhead light garage door recepticle, and one gfci plus the outlets after it. What confuses me is why this breaker trips after about five minutes with no draw except the garage door sensor beam. After replacing the 20 amp breaker(#12 wire) and the gfci outlet, it's still tripping. I thought a breaker only trips when there is a short or too heavy a current draw? Why would this breaker act like it gets hot and trip after five minutes with such a light load? Could there be a reason breakers act in this manner otherwise, bad ground/nuetral/loose wire in the box? I didn't check the tightness of the white or ground when i replaced the breaker. Is my only other option is to start pulling and retightening all the outlets and ceiling light wire nuts etc?

Teetorbilt 12-29-2005 09:35 PM

md will be patrolling shortly, wait for it.

mdshunk 12-29-2005 09:59 PM

There must be something putting a heck of a load on that breaker. A breaker that is only slightly overloaded will can take quite a while to trip.

Your first course of action is to get an amprobe and check the current draw on the conductor right at that breaker. If this is a 20 amp breaker that takes about 5 minutes to trip, I suspect you'll read something like 24 amps or so. There may well be something like an outdoor receptacle or a post light wire feed on this circuit. These are the usual suspects for "slight overloads". Outdor receptacles draw damp really bad inside, slightly shorting out in a semiconductive overload type situation. Ants and other insects can pack outdoor receptacles full of nesting type mud and such, shorting them out and overloading them. Underground UF cables to post lights and other such appurtenances can get a little nick in them over time, start to corrode and "leak" current into the earth, slightly overloading the breaker.

Another possibility is that a tight staple on one of the cables finally pinched through the insulation of the romex. Yes, it can take years and years sometimes for this to occur, when the insulation finally "cold flows" enough for the staple to contact the bare conductors. This is usually a dead short and not a overload.

IF your amprobe readings indicate a current draw more in line with what you'd expect from an idle garage door opener, you have just diagnosed a bad breaker. Breakers, despite what the clerk at a home center might tell you, very seldom "go bad". A breaker installed in a damp ambient, such as a very wet basement or in an outdoor panel in bad shape, are prime candidates for failure.

Take your amprobe reading first, otherwise you're just guessing. That's step #1. If you get a high reading, start unhooking sections of the circuit to see what section contains the equipment or device drawing such a great amount of current. Don't rule out the possibility that the GDO might be hosed up too.

flyrod 12-29-2005 10:09 PM

I suspect the outdoor post light now, we had a thaw with rain. that light has to be on that circuit being so close to the garage. Ill test the amps at the breaker and then outside. Thanks for the response, I love these forums even when i don't have a problem.

mdshunk 12-29-2005 10:18 PM

Quote:

Originally Posted by flyrod
I suspect the outdoor post light now, we had a thaw with rain. that light has to be on that circuit being so close to the garage. Ill test the amps at the breaker and then outside. Thanks for the response, I love these forums even when i don't have a problem.

Yep, now knowing about your recent thaw and rain, I believe you're on the right track. If that post light just operates on an eye, and not a switch, its underground feeder is "hot" at all times. If you use your mind's eye to draw a straight line from the post light to the nearest garage receptacle, that post light probably feeds out of that receptacle. If you take the receptacle apart, you can disconnect the feed to the post light. You should notice a distinctively different UF cable in that box, differentiating it from the other Romexes. I always, always, always run undergound feeds in PVC conduit. UF cable does have a lifespan, and when it goes bad, you have to dig. If you use conduit, if a conductor goes bad, you can pull new conductors in the conduit without digging. UF cable sucks. Rated for direct burial? Yes. Good idea? Nope.

First thing, though. Get the post light to light up (cover the eye with black tape or turn on the switch) and turn off the breaker that you're having trouble with and confirm that your suspect post light is even on the circuit in question.

flyrod 12-30-2005 06:24 PM

great diagnosis
 
You saved me alot of time and you were 100% right. A nicked feeder to the lamp post on that circuit that only malfunctioned when the ground was wet. Thanks again

mdshunk 12-30-2005 09:06 PM

I'd like to take this opportunity to pat myself on the back.

Glad everything worked out for you.


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