Melted Wires

[Riverhart]

I work in a small community maintaining the towns traffic signals and lighting. 3 years ago a concrete flood wall was built with decorative LED lamp posts on top of the wall. After 2 years we had a few lights fail. The wires between some of the lights had melted. I pulled in new wire and just assumed it was a nicked wire. Since then we have pulled new wire in between 6 sets of lights all with the same problem.
There is two 120v circuits, each on a 15 amp breaker. The circuits do not run together, so each conduit has 3 wires only. The wire is size #10 , RHW-2, rated at 90 degrees C. My total load on each circuit is roughly 7 amps. The conduit is 1"rigid encased in concrete in the flood wall. The conduit lengths are not abnormal for street lighting so voltage drop is minimal. The circuit breakers have never tripped. The contractor did not install grounding bushings to the rigid conduit, which I'm guessing is why the breaker never trips? All 3 wires are deformed, and kinked from the high heat. The hot will always be broke in half, and sometimes the neutral is also. The break always occurs exactly in the middle of the conduit run. When we pull the new wire in it is not a hard pull, and seems smooth, so I don't think the wire is getting compromised.
The only thing not done properly is the grounding bushings. Installing these now would be a huge project, because you cannot get your hand down the access hole. So we would have to rent a crane and lift the lights off to install them.

Any ideas what would be causing this?

 

[tom baker]

What voltage and what type of wire?
What is the amp reading when the lights are on?
Did you Meg wires when repulled?

 

[synchro]

... All 3 wires are deformed, and kinked from the high heat. The hot will always be broke in half, and sometimes the neutral is also. The break always occurs exactly in the middle of the conduit run. When we pull the new wire in it is not a hard pull, and seems smooth, so I don't think the wire is getting compromised.

Where along the run is the obviously damaged wire located? Is there damage all along the way from the source of power to the center of the run, but beyond that it starts becoming less affected? If so, that might indicate that the wire is getting shorted near the middle of the run. Or, for example, is the damage only near the center of the run. Or is it all along the whole run, etc.?

 

[Riverhart]

120v, #10 RHW-2, 7 amps when lights are on.

I do not have a megohmmeter, but I don't think the insulation is being compromised when pulled in.

The damage occurs in the center. From pole to pole it approximately 50' so it happens at the 25' mark. The wire is only affected about 1 foot on each side of the break. It melts the insulation off and then starts arcing on the conduit until it breaks apart. I forgot to mention its not the same run, its happened in 7 different conduit runs. There is approximately 30 poles on the flood wall.

 

[synchro]

Is there any kind of expansion joint near where the damage is occurring?

 

[tom baker]

Interesting, 7 different locations. What is common between the locations??
You mention a bushing, so if it’s RMC, perhaps the end didn’t get teamed.

 

[infinity]

Can you post some photo's?

 

[Riverhart]

 

[hbiss]

Awww look at that wire! It didn't do that by itself. Fire the hack that pulled it!!

-Hal

 

[Riverhart]

 

[Riverhart]

There is not an expansion joint that I can see anywhere.

The RHW-2 has thick insulation. Its very hard to strip, and I see no signs of damage anywhere on the wire, other than the affected area. So I don't think the ends not being reamed would cause it.

 

[tom baker]

What size conduit?
I suggest getting a mandrel and seeing if it will pull thru.

 

[mopowr steve]

By any chance was the conductor compromised before it was pulled in. Like a damaged spot on a spool that appears every so many feet.

 

[4x4dually]

View attachment 2562676

Ummm.....that had to be pulled in like that. No way could someone or heat do that to a wire 25' from the end once it's in conduit. $.02

By any chance was the conductor compromised before it was pulled in. Like a damaged spot on a spool that appears every so many feet.

Not a bad idea....but by the looks of that image, surely it didn't come off the spool that way. Someone had to have knotted it up and just pulled it in.

 

[gadfly56]

Ummm.....that had to be pulled in like that. No way could someone or heat do that to a wire 25' from the end once it's in conduit. $.02


Not a bad idea....but by the looks of that image, surely it didn't come off the spool that way. Someone had to have knotted it up and just pulled it in.

Why you should use a spool rack when pulling, no?

 

[Joe.B]

50 feet from pole to pole, but each is on it's own circuit? How far from any given breaker to the light it serves? Someone mentioned voltage drop and that's where my brain went immediately. Upsize the wire next time you have to replace it?

 

[Another C10]

I've never seen that scenario, as others mentioned it does look like the pull itself caused the stress, then with moisture finding the broken insulation allowed for the leaking voltage which in turn created the arcing allowing for the fracture.

Just my theory.

 

[Another C10]

The RHW-2 has thick insulation. Its very hard to strip, and I see no signs of damage anywhere on the wire, other than the affected area. So I don't think the ends not being reamed would cause it.

all it takes is a pin hole opening

 

[Another C10]

Awww look at that wire! It didn't do that by itself. Fire the hack that pulled it!!

Or put the hack on the pulling end, the feeding end is much more critical.

 

[ActionDave]

I think it's the fault of whoever pulled it as well.