Mystery Open Hot

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walklong

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First post, need some feedback/check my logic.

I'm semi-retired and have about 30 years of residential/light commercial electrical experience so I'm conversant with (if slightly rusty) terminology and theory. I'm trying to help a buddy out with in an older (40's?) single family residence that's been converted, first to professional office then to student rooming house. Wiring is a mish mash of several eras of NM cable.

Immediate problem is in the kitchen which is being renovated by my buddy. I recently ran two new 20a dedicated circuits to the microwave and the refrigerator. There are two GFCI devices serving counter tops, fed from above, that are now, unexpectedly dead (I know that both were functioning when I was on the site previously). My present theory is that, during installation of cabinets above these devices, my buddy managed to cut the hot conductor without tripping a breaker. (Alternatively, the breaker MAY have tripped, un-noticed and was reset when a tenant discovered something not powered - but the one tenant I spoke with today was not the guy.)

This panel has little (no?) useful labeling and all of the breakers are set and functioning (I can measure 120 v at the breaker lug and I've checked and tightened all the visible connections). Apart from dismounting the cabinets and opening the walls at the likely locations of damage, any suggestions for determining where the open is or, alternatively, determining which circuit I'm dealing with? (I don't own and won't be obtaining a sophisticated/expensive tracing tool).

TIA for any and all help.

Bill
 
You can buy a basic circuit tracer at a big box store for $40 to $60.

The first thing I would do is see if the gfcis will test and reset. If they wont, I would pull them and check the wiring. The new gfcis self test, and if they failed a self-test, they will lock out power.

Welcome to The Forum
 
walklong said:
First post, need some feedback/check my logic.

There are two GFCI devices serving counter tops, fed from above, that are now, unexpectedly dead (I know that both were functioning when I was on the site previously).

Apart from dismounting the cabinets and opening the walls at the likely locations of damage, any suggestions for determining where the open is or, alternatively, determining which circuit I'm dealing with? (I don't own and won't be obtaining a sophisticated/expensive tracing tool).
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If the circuits are fed from above is there attic access ? If you can get to the cables from above then you can use a non-contact voltage sensor (cheap) to see if the cables are live to that point.

I would pull those GFCI receptacles and make sure there is no power there or to see what's really been cut or is open. Could be an open neutral ( again a voltage sensor comes in handy).
 
growler said:
If the circuits are fed from above is there attic access ? If you can get to the cables from above then you can use a non-contact voltage sensor (cheap) to see if the cables are live to that point.

I would pull those GFCI receptacles and make sure there is no power there or to see what's really been cut or is open. Could be an open neutral ( again a voltage sensor comes in handy).
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Second floor bedroom directly above (with power at devices) I confirm (NC voltage sensor) no voltage at either counter GFCI. Now 90% certain breaker was not tripped. My guy doesn't trust stud finders - his method is drilling holes to find the stud AND determine center (keeps drilling until he locates the edges). He's cut wires before which is what I suspect he's done here. Just unusual that breaker didn't trip Square D, not FPE.

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walklong said:
Second floor bedroom directly above (with power at devices) I confirm (NC voltage sensor) no voltage at either counter GFCI. Now 90% certain breaker was not tripped. My guy doesn't trust stud finders - his method is drilling holes to find the stud AND determine center (keeps drilling until he locates the edges). He's cut wires before which is what I suspect he's done here. Just unusual that breaker didn't trip Square D, not FPE.

Sent from my SAMSUNG-SM-G930A using Tapatalk
Click to expand...

If he managed to graze it without touching the neutral or ground that would do it. No path to ground, no trip.
 
hbiss said:
Could have cut the hot side of the NM without hitting the ground or neutral. My problem with that theory is doing it twice. These are two separate circuits?

-Hal
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doubtful two circuits - just cannot see/find any logical point from which the devices are fed - I'm in Missouri and there's no licensing/regulation of the trade: my 14 year old granddaughter could buy a business license at city hall and call herself an electrician. City follows code but there's no telling who did the retro work I'm dealing with. The NM is flopping around loose in the wall cavity (I was actually jerking it around, hoping to cause a short that would trip/identify the breaker. I'm going to try and isolate the circuit by setting loads on everything in the house and then checking for a breaker not carrying a load with my meter. Not sure that will work with the kind of stuff I can plug in.
 
gadfly56 said:
If he managed to graze it without touching the neutral or ground that would do it. No path to ground, no trip.
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Yep, that's what I think happened - and if that's true there's only a couple of places it could have happened - just need to take down all the cabinets and then start opening the lath & plaster walls until we find the fault - :?;)
 
Would it make sense to disconnect the suspect cable(s) and run new rather than try to locate a fault hidden somewhere in a wall?
 
Nonmetallic cable that is fished Will Spring away from a screw, unless it's so long that it depends it to the outside wall. if it is stapled, it would be along the flat side, and any screw penetrating the cable would likely hit the ground wire as well as the ungrounded conductor. I suppose screws could be responsible for your problems, however I don't find it very likely.
 
JFletcher said:
Nonmetallic cable that is fished Will Spring away from a screw, unless it's so long that it depends it to the outside wall. if it is stapled, it would be along the flat side, and any screw penetrating the cable would likely hit the ground wire as well as the ungrounded conductor. I suppose screws could be responsible for your problems, however I don't find it very likely.
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When I read the posts about a screw being the culprit, I envisioned it happening where the NM is in a bored hole in a stud and an extra long screw, as opposed to it happening in the wall cavity.
 
walklong said:
just need to take down all the cabinets and then start opening the lath & plaster walls until we find the fault - :?;)
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There is always a chance that the fault is not behind the cabinets. It could be just a coincidence that the power went out as the cabinets were installed.

I was at a service call not long ago where the homeowner assumed that the siding guys had hit a cable and damaged it. Turned out to be a loose connection in a junction box (buried).

That little circuit tracer that Fletcher mentioned from Lowe's or HD may be worth the investment. I thinks it's less than $50. The labor to take down and reinstall those cabinets will be worth more than that.

If you are pretty sure it's behind the cabinets and there is any room above the cabinets then cut a hole for an old works junction box above the cabinet and pull the loose cable out and examine it visually. You may need a junction to splice the cable anyway. Make sure the box is in the same wall cell as the cable.
 
Besoeker said:
Would it make sense to disconnect the suspect cable(s) and run new rather than try to locate a fault hidden somewhere in a wall?
Click to expand...
Unfortunately, because the breaker wasn't tripped I cannot identify the affected circuit - the devices in the wall in the room directly above are all powered - are they on the same circuit but located before the fault, or simply on a different circuit? Until I know what circuit is affected and shut it off, I have a live, open hot, potentially with a screw in it, that, at some point, might begin arcing in a wall cavity with well seasoned framing and lath & plaster covering.
 
walklong said:
Unfortunately, because the breaker wasn't tripped I cannot identify the affected circuit - the devices in the wall in the room directly above are all powered - are they on the same circuit but located before the fault, or simply on a different circuit? Until I know what circuit is affected and shut it off, I have a live, open hot, potentially with a screw in it, that, at some point, might begin arcing in a wall cavity with well seasoned framing and lath & plaster covering.
Click to expand...
WAIT....this a good place to test an AFCI...





not really.
 
walklong said:
I'm trying to help a buddy out with in an older (40's?) single family residence .
Click to expand...

A good place to check for faults in a house that old is the light fixture junction box in the middle of the kitchen.

They used to use 100W lamps in those fixtures and there wasn't really any insulation between fixture and junction box. This would turn the junction box into and easy bake oven. You will find a lot of burned wiring in that location.

They would use this as a junction for the receptacle circuit. This old house 101.
 
growler said:
A good place to check for faults in a house that old is the light fixture junction box in the middle of the kitchen.

They used to use 100W lamps in those fixtures and there wasn't really any insulation between fixture and junction box. This would turn the junction box into and easy bake oven. You will find a lot of burned wiring in that location.

They would use this as a junction for the receptacle circuit. This old house 101.
Click to expand...


Thanks for this - I've got three ceiling fixtures in this kitchen, all on a loop from a double gang box in the same wall as the cranky GFCI's, a good place to check before blasting holes.
 
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