Strange electrical problem

[MushCreek]

I was playing around with a 120V motor yesterday, and killed one of the circuits in my shop. I plugged it in, and barely heard a little 'click'. I checked the breaker; it was fine. It didn't pop. I still couldn't get any juice at the outlets, so I replaced the breaker just in case. Still no go. I have 120 at the breaker, but even at the first junction, there's no power. Evidently, the wire failed somewhere between the breaker and the first junction. The wire is one piece, not spliced or anything. Unfortunately, I'll have to take a lot apart to get at it, so I guess I just won't have power at that end of the shop for a while.

Why would undamaged 12 gauge NM fail? Why didn't the breaker trip? Isn't that what it's there for? I can visually see about 3/4 of the NM, and don't see any damage or burns. And now, I have to figure out why the motor did this. I checked the leads, and don't have a short to ground.

 

[oldcpecdr]

Any GFI receptacles on the circuit ? Did you trip one?

Connections tight at the panel or first receptacle ?

That would be my first two places to look.

Mike B

 

[nadogail]

GFCI Receptacles make a Click Sound when they trip.

 

[kd3pc]

not sure whether you have multiple outlets or just one on the "circuit". It would be odd to only have one outlet.

I would take apart each outlet and check for arcs/burns/etc. It is unusual for the wire to fail, not saying a screw or nail could have been close enough to arc over.

Once you have every outlet apart and see no apparent damage, then shut the power off. Break out your multimeter and check for continuity. then for voltage.

 

[MushCreek]

I did some more checking, and it's actually in the NM somewhere. I ran another piece temporarily, and everything is fine. Somehow, it failed in the middle without tripping the breaker.

 

[rlitman]

I did some more checking, and it's actually in the NM somewhere. I ran another piece temporarily, and everything is fine. Somehow, it failed in the middle without tripping the breaker.

I've seen that happen. Most times it's where someone put in a staple too tightly and pinched the insulation, or when the clamp at the box is too tight, doing the same.

 

[MushCreek]

Unfortunately, part of the wire is buried in the wall, so I may never find out for sure. I'm going to run a new wire via a different route so I don't have to take the wall apart.

 

[Jim greengo]

Any GFI receptacles on the circuit ? Did you trip one?

Connections tight at the panel or first receptacle ?

That would be my first two places to look.

Mike B

That would be my guess.

 

[wyliesdiesels]

Did you take the outlet out of the j box and check the connections?

If so, then the wire has some damage on it somewhere maybe a staple?

 

[MushCreek]

I checked the continuity of the wire. White and ground have continuity; black does not. It has nothing to do with outlets; there's a junction box before any outlets. Must be damaged wire, although why it chose now to fail, after 8 years, I don't know.

 

[wyliesdiesels]

I checked the continuity of the wire. White and ground have continuity; black does not. It has nothing to do with outlets; there's a junction box before any outlets. Must be damaged wire, although why it chose now to fail, after 8 years, I don't know.

Black doesnt have continuity to what?

 

[CoogarXR]

Could be a mouse-munch if it's in the wall somewhere.

 

[MushCreek]

To itself. I checked the wire for continuity. Put each end on the meter, and you get nothing. There's a full break in it somewhere. Could be a mouse munched on it; I have trouble with mice in the winter.

 

[wyliesdiesels]

To itself. I checked the wire for continuity. Put each end on the meter, and you get nothing. There's a full break in it somewhere. Could be a mouse munched on it; I have trouble with mice in the winter.

Oh you checked continuity from the wire in the panel to the wire on the outlet? Gotcha

 

[spudley]

Did you put anything on the wall recently over the wire path. Or maybe a drywall nail or screw puncture? Maybe the motor draw was just enough to break whatever was left.
I'd tear the wall down to find it cause that would drive me nuts (yes it's a very short ride).

 

[sparky 1971]

Not to be a smart a$$, but are you 100% sure you checked the right breaker? It wouldn't be the first time a panel was marked wrong. If it's the wrong breaker, you were checking for continuity on the wrong wire. Just for fun, use a meter and check all the breakers.

 

[nh_yota]

I'm no electrician, but I've never seen undamaged NM fail. On the other hand I've seen plenty of situations where it's damaged by a box clamp or staple but that always causes a short.

 

[Mattlt]

Could be a mouse-munch if it's in the wall somewhere.

This.

 

[KenC]

Is it possible that the receptacle you think is the first is not? I have seen more than one case where the breaker was wired to a box on the other side of the wall before continuing. Think outside recept that is a GFCI.Builder used that to meet both needs, outside GFCI and living space circuit protected also.

 

[WisJim]

I've had mice damage and short out wire 4 or 5 times in our house, sometimes where the wiring is hidden and sometimes at a box, so I can believe that a hidden short could happen. At the present time, I have a short between the wall switch and the ceiling fan in the bathroom and the smell of dead mouse tells me the cause. I've had numerous cases of a mouse chewing the wires at a box and being electrocuted.

 

[wyliesdiesels]

I've had mice damage and short out wire 4 or 5 times in our house, sometimes where the wiring is hidden and sometimes at a box, so I can believe that a hidden short could happen. At the present time, I have a short between the wall switch and the ceiling fan in the bathroom and the smell of dead mouse tells me the cause. I've had numerous cases of a mouse chewing the wires at a box and being electrocuted.

A critter chewing on one conductor would not cause a short. It would cause an open like what the OP has.

A short would cause the breaker to trip.

 

[raco232]

Never heard of or seen, a copper eating mouse. I bet someday you’ll find the answer to the mystery!

 

[KenC]

A critter chewing on one conductor would not cause a short. It would cause an open like what the OP has.

A short would cause the breaker to trip.

Copper/critter/metal box. Short, at least for awhile.

I have an occasional problem with squirrels on the pole/transformer that supplies my shop. I'll walk in and one phase of my 240/3ph will be dead. Then I look at the base of the pole and see a little furry carcass. Circuit protector above the transformer is kicked.

3/4 times so far in 12 years.

I still am amazed at how quickly the city utility crew can reset that with a 20+foot wiggly hot stick!

 

[Falcon67]

>although why it chose now to fail, after 8 years, I don't know.

It was waiting for just the right time to piss you off. "Inanimate objects" my ***.

 

[rlitman]

A critter chewing on one conductor would not cause a short. It would cause an open like what the OP has.

A short would cause the breaker to trip.

Mice will not chew through a 14 AWG copper wire. They just don't have the teeth for that.

 

[nadogail]

A critter chewing on one conductor would not cause a short. It would cause an open like what the OP has.

A short would cause the breaker to trip.

A critter chewing on the insulation of a conductor could facilitate a short.

 

[mark#3]

Using a 40' extendo stick to open a transformer cut out in the wind does require technique

 

[Marctrees]

Mushcreek - I do not think the question was ever answered - Is it a GFCI protected circuit, and was that GFCI checked ?

Is the breaker that feeds this ckt actually in the shop ?

How many recept ckts feed this shop ?

Do you have an outdoor recept anywhere near the shop ?

Please answer all questions fully as you can.



GJ Sparkies - When tripped, do GFCI receptacles open only hot ? or both hot and neutral ?

Marc

 

[Marctrees]

Although anything is possible, based on the info so far I'm betting there is a GFI recept between panel and this "First" ?? J box.

Pretty tough w the limited info so far.

Marc

 

[MushCreek]

No real answer yet. The wire goes from the breaker to a junction box. From there, it goes to various outlets on that end of the shop, and one outside. Yes, there is a GFCI outlet, but it's AFTER the junction box. When I tested the circuit, there was no power to the junction box. No breakers were tripped. I even replaced the breaker on that circuit, thinking perhaps it was faulty. I wired the shop, ad everything is labeled, so I know which circuit is which.

I did a continuity check from one end of the NM to the other, and it's open. The part of it I can see shows no physical damage, so the break must be in the wall. There it shall stay for a while, because I'm not tearing the wall apart. I re-routed another new piece of 12 ga. NM to the junction box, and all is well. Some day I'll have that wall apart when I insulate and finish the shop; perhaps then I'll find the problem.

 

[APEowner]

I don't know if it was a mouse or a squirrel (I suspect the latter) but something ate a bunch of the electrical cords in my shop over the winter. They severed the cord to my parts washer, ate most of the way through the power cord on the MIG welder and stripped a good eight inches of insulation and a good part of the conductors on the foot control for the TIG. For a while this spring it seemed like every project involved a cord repair before I could really get started.