Breaker tripped under no load?

Question

Came home tonight and found my hall light didn't work when I flipped the switch. Went to the panel and found the breaker had tripped.

The only things on this circuit that I know of, based on what stopped working, are: - hallway light - closet light - half bath lights and fan

All of these things were working this morning. I know because I used all of them. All of them were also turned off before I left. Normally, when, I've seen a breaker tripped, there's something obvious like a hair dryer, space heater, or a short or ground fault. This one is so odd because it seems to have tripped while nothing was drawing current.

I have two theories:

• The breaker is old and beginning to fail. I've read they can start to trip at random as they wear out. This house is over 100 years old. The electrical is definitely newer than that, but I am not sure how old it is. I suspect maybe sometime in the 90s at the earliest from looking at the panel labelling.
• One of the switches for the listed lights shorted when I turned it off. If it was the last thing turned off, no one would have noticed anything. In this case, I suspect the closet light, as it's a pull-chain type fixture that doesn't seem well mounted. Maybe the wire shorted against the box?

So, here is my biggest question: can a failing breaker trip when there is no current drawn? That is, when everything on the circuit is off? If the answer is no, the problem is definitely a short or ground fault somewhere. If it can, I suppose I can replace the breaker.

I welcome the experts' advice. For the time being, I've left the breaker on the OFF position for safety.

Answer 1

This more of a comment than an answer, but I can't post comments because I don't have enough brownie points yet!

Anyway, had an identical problem at a home I used to live at. First symptom was the circuit supplying the freezer in the garage kept tripping, so I thought dang, bad freezer. But plugged into another circuit and it was fine, no tripping. The circuit the freezer used to be plugged into kept tripping. Then we lost some outlets and lights in the living room (shared wall with attached garage).

OK, now what!? Crawled up in the attic and found the cabling where it went thru the top plate had been chewed thru my mice! There was a dead one right there in the hole. But it only explained part of the problem because the living room lights were on a separate circuit. I pulled some outlets to do continuity checks and they failed. So I pulled the sheetrock off the garage side of the shared wall and found more mice had chewed thru cables along with a large mouse nest. The electrocuted bodies where still there. I counted my lucky stars the breakers did their job and my house didn't burn down. Had to do a reasonable amount of re-wiring, but again, very glad I had a Square D QO panel and not Zinsco panel!

I share this story because it sounds similar to your problem. Shorts and tripped breakers without known reasons are scary and cause for concern. Good Luck.

Answer 2

I would check that closet light in any event, inspect the wiring inside the box carefully, and re-mount the fixture so it's secure as it should be. (Even if the breaker didn't trip you'd want to fix that.) It's very possible there is a pinched wire, stray wire making short, or something else in there that caused a short when you pulled the chain.

It's more of a hazard when a breaker fails to trip than when it trips unnecessarily. But it wouldn't be a bad idea to replace it if it is old and there's been a short.

Answer 3

Circuit breakers scan tart to nuisance trip when they have tripped and been reset many many times; the current sensing elements can develop what's called a "thermal memory", meaning they no longer return to their original state, so it takes less and less current to make them trip the next time. If your breaker has not been repeatedly tripping, it's not "worn out".

Most likely your pull chain switch has failed and caused a short circuit. There are two kinds of sensing elements in most circuit breakers, a thermal trip that responds to long term overloads that increase slowly, and an instantaneous trip that responds to immediate short circuits, i.e. not waiting for the current to build up. When switch components break off inside of old worn out fixtures, they can sometimes land in places that cause short circuits, in which case your breaker did EXACTLY what it was supposed to do, prevent a fire.

Answer 4

With all loads turned off, reset the breaker, if the breaker holds turn on each light switch one at a time when it trips that's where to start looking. I agree with the other guys closest light is probably the culprit, a specialy if it's a pull chain type fixture. If it's not the problem, and you don't have Ark Fault type breakers, then it's time to start searching... If there are recepticals on that circuit, make sure they are properly "pigtailed" and wires are terminated by screw type connections, not back-stabbed! Loose connections via back-stabbed devices are the majority of residential service calls and fires! Which is why code now requires Arc-Fault type breakers. Hope this helps!!!