Heated Ground Wire in AC Circuit

[Will Wire]

I was referred to a job recently to repair an AC circuit in a home because the Romex jacket was torn and the ground wire was exposed. When I inspected the jacket I realized that the ground wire had gotten so hot that it had melted the Romex jacket the entire length of the circuit. The circuit conductors were not damaged at all. If anyone has ever seen this and/or has any suggestions as to why this would happen I would appreciate any information. Thanks, Trent

 

[LarryFine]

Presuming proper wiring to begin with, my first guess would be a bad service neutral. Something is making one end of the EGC electrically hot, and it may be the panel end, and the freon lines are bonding the AC somehow. Here's why I say that:

I once responded to an emergency call for an electrical fire. The EGC to the water heater start a fire during a storm that apparently caused the incoming neutral to become energized. It was still hot after pulling the meter, I was told.

An illegal service upgrade (made obvious by the 60a line-side cable and 200a load-side cable at the meter, plus a dozen or so other issues) had been done. The closest thing to an electrode was the #10 EGC in the NM to the water heater.

Of course, it may also be a fault within the AC unit, and the EGC has too much impedance to trip the AC breaker, although the faulted conductor should theoretically be carring more current. Maybe the insulation is providing, well, insulation.

 

[ActionDave]

Point of clarifcation- Are you looking at charred sheathing or thin, distorted sheathing? I have seen bad reels of uninstalled Romex. The wrapper was so thin you could see through it right along the bare conductor.

 

[LarryFine]

Point of clarifcation- Are you looking at charred sheathing or thin, distorted sheathing? I have seen bad reels of uninstalled Romex. The wrapper was so thin you could see through it right along the bare conductor.

Same here, now that you mention it. I've seen the wrapper not positioned correctly, and the sheath was stuck to one of the conductors for almost the entire roll.

UF would have been better. I used it up on long home runs, which has fewer strips per foot.

 

[Will Wire]

The sheathing was charred sheathing that had melted away.

 

[Pierre C Belarge]

I would say that:
A. the wiring installation was incorrect and the EGC may be either the grounded or ungrounded conductor that has made improper contact with a bonded surface.

B. the EGC has high resistance and there was a ground fault, unless of course you are going to reset a breaker that has already opened due to the fault condition.

 

[TobyD]

Possible lightning strike.Strange but I've seen plumbing pipes so hot that the solider has melted from the joints due to being hit.

 

[Dennis Alwon]

Possible lightning strike.Strange but I've seen plumbing pipes so hot that the solider has melted from the joints due to being hit.

This is what I thought immediately but who knows. :grin:

 

[brian john]

1. Have you measured current on the EGC?
2. Have you measured voltage from hot to EGC and neutral to EGC?
3. Measure current on the NGB in the panel you may have to install a temporary NGB and lift toe permanent NGB.
Measure current on each feeder conductor and the grounded conductor.
4. Perform zero sequence measurements on each circuit (neutral and all energized conductors associated with the circuit) also perform zero sequence on the main service conductors.
5. Check all connections with particular attention to the neutrals
6. Isolate each circuit, with power off and megger from energized to neutral and energized to EGC and EGC to neutral.
7. Listen to all post above in addition to verifying the above.

There may be more to check but it is early for me, oh and these are not in any particular order.

 

[realolman]

Captain Obvious here:

The EGC had too much current on it.

I know how obvious that is now , but much of the preceeding posting is very confusing to me..

Do you suppose the deduction that the EGC had too much current on it is correct ...and we could start over, and go from there?

What size romex? what kind of AC circuit?

 

[SEO]

I went on an electrical fire inspection and found the same thing only it actually started a fire. I can't go into a lot of details but what happened was someone plugged a meter in for seperately metered AC and the ground wire was touching the load side of the meter socket. It energized the ground wire and took a high impedence path back to the source thru the AC condencate line to the furnace back to the panel then to the meter. What actually caught fire was the furnace circuit which went thru the attic.

 

[realolman]

The circuit conductors were not damaged. Only the EGC

Is that because the insulated conductors can withstand excessive heating better than the EGC? ... or because the insulated circuit conductors were not involved?

 

[SEO]

In the case I looked at the circuit conductors were not involved in the fault. The equipment grounding condutor in the circuit to the furnace was the weak link and heated until it opened but created a fire in the process.

 

[brian john]

Captain Obvious here:

The EGC had too much current on it.

I know how obvious that is now , but much of the preceeding posting is very confusing to me..

Do you suppose the deduction that the EGC had too much current on it is correct ...and we could start over, and go from there?

What size romex? what kind of AC circuit?

Just out of curiosity did you read any of the previous post?

 

[realolman]

Just out of curiosity did you read any of the previous post?

Yes I did. Why would you ask me that?

Are we trying to show how educated and intelligent we are , or are we trying to assist the OP with a problem?

Did YOU read them? What am I missing?

 

[brian john]

Yes I did. Why would you ask me that?

Are we trying to show how educated and intelligent we are , or are we trying to assist the OP with a problem?

Did YOU read them? What am I missing?

All the issues you raised were covered.

 

[realolman]

All the issues you raised were covered.

There were two posts regarding defective romex from the maunfacturer, so the excessive current on the EGC was not yet apparent at that point, or the posts were irrelevent.

One mentioned using UF instead of romex.


I don't know what this means at all:

the EGC has high resistance and there was a ground fault, unless of course you are going to reset a breaker that has already opened due to the fault condition.

The OP then re-stated that the EGC was so hot that it melted the sheathing.

Then a couple of posts speculating about lightining strikes and the melting of copper pipes.

What percentage of people reading this forum do you suppose know what a zero sequence test is , how to perform it, or why it would be useful? I am one who does not.

At that point I felt the darts had been scattered all over the wall, much less the dart board. I thought maybe a re-focusing on the problem and facts at hand was in order... I DID refer to myself as Captain Obvious....

 

[TobyD]

Sometimes things are so simple we tend to confuse ourselves.LOL.Without actually running an evualation on the problem mentioned I can only speculate.God only knows ....