Locating hot-to-equipment-ground short

[oldchap]

Friends,

In a new residential construction after rough-in passed, then later the outside siding and inside drywall installed, we now have a short between the hot and the naked copper ground in one NM cable. We suspect a nail or screw that we can't find. Does anyone know of a TRACER capable of locating a short in in-the-wall wiring? Second, does anyone have successful experience with ANY moderately-priced tracer that locates in-wall wiring circuits, energized or de-enegized? Which one(s)? I see a good many negative reviews. Are there positive ones from you experienced electricians?

Thanks!

 

[Dennis Alwon]

I have located nails thru a wire by isolating what wire is shorted. I would then plug my tester into the neutral side of an extension cord that is plugged into an energized circuit. The other tester lead would simply get applied to the nails in the siding around where the wire may be.

IMO, you should just eliminate the wire and run a new one even if you can pull the nail out and clear the short.

 

[wooleybully]

wooleybully

wooleybully

fluke makes a good tone tester, it will help locate where a wire is in the wall, but you have already identified the problem, [ short ] it would be best to abandon this wire, clearing a short by pulling the nail out wont fix the arc blast damage to the wiring, yes it will work if not seperated but the resistance will be very high, and wire very brittle and circumference probably reduced, creating a fire/safety hazard. i would isolate this run between boxes if possible, you can find short between two boxes by toning for continuity, make sure all your light switches are off so you dont get false ground to hot.good luck

 

[G._S._Ohm]

If it's a bolted short pass 10 A or so into the cable through a load resistor or toaster or hair dryer.

If the short is at the 50' mark of two conductor #14 copper then you will read 2.6 vac across the ends of the cable. With resistance this low be sure that the leads you measure voltage with do not touch the leads that supply the current.

For exactly 50' and exactly 10 A I'm not sure how close to exactly 2.6 v you will read - in other words, a reasonable tolerance you can expect using this method.

There's always TDR to find the fault within 0.1'.

 

[hillbilly1]

Amprobe makes an excellent tracer for this, I use a 9 volt battery to power the circuit, since it does not inject a tone, like most tracers, you will find exactly were the short is, you just follow the wire in the wall until the signal disappears. It actually looks for current that is drawn from the circuit at a certain frequency. I have located shorts behind sheetrock within a 1/2" using this method and tracer. About $900 for one though, but if you do a lot of troubleshooting, it's well worth the money.

 

[petersonra]

You know which circuit it is. Instead of trying to fix it, just run a new circuit. It will be more cost effective.

 

[SG-1]

Try disconnecting the naked copper ground ( EGC ) so the breaker cannot trip ( no current flow ). Then use a non-contact type volt meter to locate the energized nail head. Or as Dennis suggested a voltmeter & extension cord.

I think Wollybully's idea is excellent.

No offence G.S. Ohm, but 10 amps might cause the damaged conductor to glow inside the wall. IMHO, this fault is unlikely to be of the bolted type.

 

[G._S._Ohm]

10 amps might cause the damaged conductor to glow inside the wall.

Good point. This method may work in principle but it is not a safe way to have the fault show itself.
I should have said that if you get abnormally high resistance readings (more than you would expect from, dunno', 100' of two conductor #12 or #14) abandon the method immediately.
This forum has taught me and is teaching me, a lot.

 

[SG-1]

Good point. This method may work in principle but it is not a safe way to have the fault show itself.
I should have said that if you get abnormally high resistance readings (more than you would expect from, dunno', 100' of two conductor #12 or #14) abandon the method immediately.
This forum has taught me and is teaching me, a lot.

That is why I have been ganging out here too, for the education .

I've been thinking, if he has a thermal imager...

 

[John120/240]

Tear off the siding or open up the sheetrock to find the short & prove your point.

But really, just run a new circuit & charge the offending party enough to cover all

headaches.