What's it take to trip a breaker?

My mother’s house…a few outlets quit working. I couldn’t easily find the problem, didn’t have the time, and called in a sparky. After 2 hours, he found a romex wire that had “burned” in too. I was shocked that the breaker didn’t trip. He said it would not trip the breaker if a wire burns.

Wouldn’t that condition be classified as a short and shouldn’t it trip a breaker?

Wires don’t “burn in two”. I think you would have to find out what really happened. I would guess that a wire was broken due to some kind of mechanical damage and created an open circuit as opposed to a short circuit.

If it was a nicked wire with a much smaller cross-sectional area, a high current could cause a hot glowing spot that may eventually weaken the wire to the point of it becooming brittle and breaking. If this happened, it was a bit of a miracle that a fire didn’t start.

Think AFCI

Yes, a nick is what I was referring to by mechanical damage. Agree.

I agree - this type of failure is almost exactly why AFCIs were created and are now required in many locations.

Was it aluminum wiring by chance. This type of thing is much more common with aluminum wiring.

As an electrical inspector, I see this type of situation regardless of it being copper or aluminum.

Some “glowing” arcs and other arcing incidents will lead to cable or even devices that melt and eventually separate themselfs from the circuit without opening a circuit breaker.

Yes, that is the premise of why AFCIs have been developed.

Copper non-metallic sheathed wire. But an FPE panel…that’s the part that has me concerned. House was built about 1973.

Well, that’s a pretty important piece of information you left out. Lacking that, the knicked wire is the likely root cause. With the added information that this was an FPE panel, it may well have been some sort of overload that just used the weakest spot of all the wiring as the “fuse”.

Agreed…While this problem on the surface would lead someone to blame an FPE breaker itself…in this case I would agree that chances are you had a nick or damage to a wire that became a weak spot…which leads to a smaller surface area on the conductor which leads to it’s failure.

If he FPE still bothers you I would suggest a good inspection by an electrician who is very familiar with FPE products. While th FPE did not trip as it probably would no have on other breakers as well…unless it results in a ground fault because of the condition.

This is exactly why AFCI’s are here today and more so why the NEW combination versions are demanded in the 2008 NEC…sounds to me like a classi series arc.

I left it out on purpose because I didn’t want everyone jumping to conclusions about FPE being the likely cause.

I want to thank everyone for their valuable input.

That would be a perfectly reasonable conclusion too, in that case.

I realize that I don’t have to respond to stuff on this site, but I choose to anyhow. Purposely leaving out information you have from your post is completely “uncool”. You can screw around with someone’s time if they are your student or on your payroll, but if you’re looking for answers from experts, give all your information. If the purpose of your post was to educate others, say so up front so that those who might choose not to spend their time on posts like that are fully informed, up front.

No offense was intended. I left out the panel being FPE because I KNOW FPE is an issue in itself. I was wondering if there was another reason or electrical condition that prevents a breaker from opening besides simply a defective breaker or panel design (I am not an electrician). I feared had I said initially that it was an FPE panel, that the thread would have turned into a discussion of the hazards of FPE, of which I am well aware. I’ve read this board enough to know that FPE excites a lot of folks.

Your comments are appreciated and I’m sorry if you felt I acted inappropriately.

Good GAWD!!!