K&T/120 volts to ungrounded wire mesh

[phattonmvp]

9 unit 100 year old building. (1ph 120/240) Some knob and tube still being used. Here's the issue. Some of the wire mesh in the plaster walls has 120 volts going to it. There are two panels in this building. I've found that by shutting off the main in panel "B" it kills the power going to the mesh. BUT- with the main on, and by turning off the individual branch circuits, I still have 120 volts going to the mesh. I've isolated the problem to the "A" phase. I replaced the service entrance cable hoping that since shutting off the main (or even just the A phase) got rid of the 120 volts to the mesh that it might cure the problem....... but it didn't. I'm looking for troubleshooting hints that minimize demolition. I know taking out all of the K&T would more than likely take care of the problem, but I really want to find the source. Thanks, PH

 

[peter d]

Try shutting the circuits off one at a time.

 

[rbalex]

Assuming your discription is accurate, the fault must lie between the loadside of the main breaker and the branch circuit breakers; possibly in the main breaker itself.

 

[SEO]

Welcome to the forum. Do you have 240 volts when you go from the mesh to the "B" phase?

 

[ceb58]

Assuming your discription is accurate, the fault must lie between the loadside of the main breaker and the branch circuit breakers; possibly in the main breaker itself.

Have you checked for voltage on the can? I just had a situation where the main breaker had a crack in the case of the breaker causing it to arc to one of the mounting screws. It in turn was sending voltage to the can.

 

[phattonmvp]

PETERD- Tried that.
SEO- Good question. I'll check.
CEB58- No voltage at can.

Thanks folks. I'll keep trying. PH

 

[76nemo]

So you are saying the 240 main in panel B is holding????

 

[phattonmvp]

"Holding" Not tripping. Yes- It is not tripping because the mesh isn't grounded.

 

[76nemo]

Let's reword this. What problems are the units experiencing on the second panel??????????????????

 

[phattonmvp]

None. There are no problems on the surface. Nothing that anyone would notice. We're doing some minor remodeling and noticed the problem when we tore into a wall.

 

[76nemo]

How did you come to the point to measure V on the mesh? Is anyone getting juiced? If that's the point, the answer must be somewhat simple, and a very easy way to go about it and figure it out:wink:

 

[76nemo]

Well then, first question. Are you using a high impedance meter??????

 

[76nemo]

I think I deleted your reply:-?

 

[phattonmvp]

Yes someone got shocked. I'm sorry. I don't follow your comment about being simple and easy to figure out. And - I don't believe it's a high impedance meter. I have your middle of the road Fluke and a middle of the road Amprobe. Checked the mesh with both.

 

[76nemo]

Yes someone got shocked. I'm sorry. I don't follow your comment about being simple and easy to figure out. And - I don't believe it's a high impedance meter. I have your middle of the road Fluke and a middle of the road Amprobe. Checked the mesh with both.

Your "middle of the road Fluke" is most likely high impedance, but not likely to read a full 120. Your problem sounds like it lays in the main.

Again, this sounds very simple and something is missing. Somebody is getting shocked, have you checked panel B for a legit install???

 

[ceb58]

Is any thing tapped off the load side of main?

 

[nolabama]

ground the mesh and see what trips

 

[mxslick]

ground the mesh and see what trips

Bad idea. The mesh could turn into a giant heater grid before anything trips, or whatever point of contact may heat up or arc enough to start a fire.

The wood in a building that old is most likely extremely dry and it wouldn't take much to start a fire.

It does sound like a feeder issue or a problem with whatever panel is on the load side of that main breaker.

I'd pull all the breakers from that panel and check the buss area very carefully for evidence of corrosion, arcing, carbon tracking or flashover.

 

[LarryFine]

Be 100% sure it's not your ground reference that's hot, and that you found mesh that is grounded.


I'm just sayin' . . .

 

[iwire]

I've found that by shutting off the main in panel "B" it kills the power going to the mesh. BUT- with the main on, and by turning off the individual branch circuits, I still have 120 volts going to the mesh.

Just curious, did you turn them all off at that same time, or did you turn each one off individually?

If you only turned one off at a time I would turn them all off and see what you have.

It is possible you have faults on two circuits or one circuit is actually interconnected in the walls somewhere.

Good luck. :smile: