Trouble on AFCI "again"

[acrwc10]

So I got a call from a costumer that the AFCI had tripped, I went out there and ask " have you done any vacuuming,,,,,,," and the answer is yes. So I reset the breaker and left. A week and a half goes by and the AFCI trips again ( each time they can't get it to reset ) This time I start taking the circuit apart and megger the NM box to box and find one piece about 35' long ( completely in-accessible ) that has a reading of 9.8 ohms ( on the 200 ohm setting ) from black to white, when I put the meter to the 250 volt setting it shorts out at 40 volts.
The funny thing is that The breaker holds at all. If it has a nail or something in it, I would expect a dead short or nothing. The 10 ohm reading has me scratching my head. And the circuit holds with everything on at 11 amps.
I don't want to start cutting walls quite yet. Any suggestions on tracing the wire in the wall to locate a possible sheet rock screw or breach in the wire.
Any Ideas ????
I should add that I changed the breaker from a non combination type AFCI to a combo. Just on the off chance it would have an affect on the problem.

 

[e57]

I don't want to start cutting walls quite yet. Any suggestions on tracing the wire in the wall to locate a possible sheet rock screw or breach in the wire.
Any Ideas ????
I should add that I changed the breaker from a non combination type AFCI to a combo. Just on the off chance it would have an affect on the problem.

Got spare money for a new tool? It's a learning curve to master - but better than a guess, even though interpetive....

That said I have found rock screws, hidden boxes, shorts, opens - in all kinds of wire with them.

 

[acrwc10]

Got spare money for a new tool? It's a learning curve to master - but better than a guess, even though interpetive....

That said I have found rock screws, hidden boxes, shorts, opens - in all kinds of wire with them.

I had kicked around the thought of a TDR. How long did it take to figure out the nuances of using one ?

 

[Lcdrwalker]

Greenlee has a circuit tracer with adjustable gain. I use one and the signal disapears after the fault is passed. Unit is good for 9VDC to 300VAC and is about $350.00.On high setting it will also trace underground runs.

 

[ptonsparky]

You will still need to trace the path of the wire even if you use a tdr. Getting a distance to fault won't help if you don't know the exact route of the cable.

All things considered, it might be easier to "jump" around the damaged portion. Not as much fun as using a TDR for the first time but easier.

 

[Dennis Alwon]

So I got a call from a costumer that the AFCI had tripped, I went out there and ask " have you done any vacuuming,,,,,,," and the answer is yes. So I reset the breaker and left. A week and a half goes by and the AFCI trips again ( each time they can't get it to reset ) This time I start taking the circuit apart and megger the NM box to box and find one piece about 35' long ( completely in-accessible ) that has a reading of 9.8 ohms ( on the 200 ohm setting ) from black to white, when I put the meter to the 250 volt setting it shorts out at 40 volts.
The funny thing is that The breaker holds at all. If it has a nail or something in it, I would expect a dead short or nothing. The 10 ohm reading has me scratching my head. And the circuit holds with everything on at 11 amps.
I don't want to start cutting walls quite yet. Any suggestions on tracing the wire in the wall to locate a possible sheet rock screw or breach in the wire.
Any Ideas ????
I should add that I changed the breaker from a non combination type AFCI to a combo. Just on the off chance it would have an affect on the problem.

As in any short I would separate the circuit in the middle of the run and then meg it. If it is fine then you know the problem is in the second hale=f of the circuit. Keep moving down the line til you isolate the problem.

 

[nakulak]

sometimes in a case like that, if the damaged wire is completely inaccessible, it might be easier to abandon the bad part of the ckt if there is an easier place to refeed the dead part from (from another ckt)

 

[acrwc10]

As in any short I would separate the circuit in the middle of the run and then meg it. If it is fine then you know the problem is in the second hale=f of the circuit. Keep moving down the line til you isolate the problem.

I did just that,and I know which piece of cable it is.

sometimes in a case like that, if the damaged wire is completely inaccessible, it might be easier to abandon the bad part of the ckt if there is an easier place to refeed the dead part from (from another ckt)

That is an issue as there is no access, above or below.
Any thoughts on the 10 ohm reading? like I said it seems odd to me that it isn't just an infinite reading if it is a nail or such.

 

[acrwc10]

Has anyone used the Rigid see snake to look in ceilings or take out the outlet box and look up the wall for issues like this ? A friend just bought one and I'm thinking about trying it , can't hurt.

 

[cowboyjwc]

I haven't used that one, but I have used a snake type camera, the only thing it told me is where the problem wasn't. I still had to remove drywall to find the nail sticking through the hole.

 

[M. D.]

I've a plumber for a brother ,.. nice guy though really :roll: ,.. when he needs to repair a leak in ,.. lets say the tub drain second floor ,.. he does not bat an eye ,. the sheetrock comes down ,.. pin hole leaks in copper pipes?? bye bye sheetrock,..

We electricians will bend over backwards to prevent a teeny weeny little patch.

A friend of mine ,.. he wanted a pool table light,.. he bitched and moaned about the notch I had to make at where the wall meets the ceiling so I could install the switch ,.. two weeks later he was having boiler trouble ,.I go over to help him out,.. insulators had been there,.. 2" holes cut in the same ceiling , everywhere ,.. 75 of them at least . I say "buddy whats up with that" ,.. he says .."oh,.. those. I can patch those,.. you will never even know they were there."

Cut the rock and get'er done

 

[ptonsparky]

We have a piece of romex that has several nail holes in it with very apparent arc & sparks. Never?? did trip a breaker and was used until a remodel resulted in the find. Your next spark may separate the wires enough to allow the circuit to operate.

Sounds like you will be patching walls one way or another so short of buying the proper equipment, take an educated guess and cut the circuit in half, test and do it again. They need more receptacles on that wall anyway.

Locate the path, back to that again, take you non contact voltage probe and run it along the wall until it lights up. Maybe you will find the guilty nail. Use sticky notes to mark the path.