Melted Wires

[mtnelect]

When I was doing traffic signal work, there was a standard rule when changing wiring:
1. Pull out all the old wiring.
2. Fill the conduit with water then blow out the conduit with a compressor to remove any debris.
3. Then pull in the new wiring.

 

[Amps]

If pulling new wires again, since you know the distance where the problem occurs, maybe you can slide some shrink tubing on the wire to that point and seal it on to give it some extra padding, then pull it through ?

 

[Riverhart]

I appreciate all of the suggestions. If I have time I will pull out the first run of wire we replaced last year, to see if it's failing. The comments are leading me to contractor error.

 

[tom baker]

That’s a likely cause, perhaps one person pulling, wire got a kink and was jerked into pipe. And no bushing as pointed out

 

[augie47]

You mentioned failures on multiple runs. Once the wiring has been replaced, have there been any failures ??
I agree with others in thinking it involves human error not mechanical/electrical;.

 

[winnie]

If I saw that sort of damage on a single set of wires, or in random locations, then I would agree: minor physical damage such as pinholes in the insulation, leading to high impedance faults (current flow from insulation pinholes through water or similar), leading to heating, insulation breakdown, and complete failure.

But the OP is describing multiple failures from multiple wire installations, but all in the same place, right in the middle of a 50 foot conduit run.

I'd be looking for something specific to those locations.

Is there some sort of fitting at the failure points? Perhaps we are seeing the wire rubbing on a fitting due to daily temperature cycles, eventually cutting through the insulation.

The next time there is a failure, you might want to pull a camera through the pipe.

Jon

 

[ptonsparky]

Ice.
Is there a chance water collects in the low points and freezes? I've seen it push the conductors through the side of emt.

 

[synchro]

Ice.
Is there a chance water collects in the low points and freezes? I've seen it push the conductors through the side of emt.

Yes, perhaps the conduit runs were not adequately supported before the concrete was poured, and it had sagged in the middle of each run.

 

[synchro]

Actually, freezing and thawing cycles might explain how sections of the wire could be pushed together and cause it to contort into tight loops as in the picture, as well as pulling it apart and causing it to break.

 

[PCBelarge]

Have you taken amperage readings with a meter placed for a few days. The damage certainly looks to me to be heat. Are the lights operating properly (current wise), are the conductors properly sized? I know you said they are. Something is creating a heat issue. Which should be evident once you pull it out. Meggering is a must.