Unexplained heating on feeder conductors

[pct2607]

We were called out to a customer's site today and found that all four sets of the feeder conductors of a 1200A service have been overheating and melting away the insulation. It appears that it was torqued because of the sharpie mark on the bolt and when my guys took it apart the nuts were tight. First glance tells me that it maybe that each crimp does not appear to have been compressed correctly, but again I'm not 100% sure. We are in the process of getting this repaired and will monitor the load for several days. Has anyone seen this before?

Thanks,
Peter

 

[Dennis Alwon]

We were called out to a customer's site today and found that all four sets of the feeder conductors of a 1200A service have been overheating and melting away the insulation. It appears that it was torqued because of the sharpie mark on the bolt and when my guys took it apart the nuts were tight. First glance tells me that it maybe that each crimp does not appear to have been compressed correctly, but again I'm not 100% sure. We are in the process of getting this repaired and will monitor the load for several days. Has anyone seen this before?

Thanks,
Peter

That is what I think... The compression wasn't done or not done well.

 

[don_resqcapt19]

It appears that they were not crimped correctly...maybe the incorrect die or not enough crimps. Look at the neutrals. Two have two crimps and two have 4 crimps

 

[ppsh]

I'm 99% sure what they used on those versa crimp lugs. A 6 ton Milwaukee crimper with a 400-750 adapter jaw, that is the only die I know of with such a narrow jaw. They require double the amount of crimps of a 12 ton, because the dies are half as wide.

The lines on the lug mark the area to be crimped, but it looks like they just put one crimp on each line instead.

Take a look at the neutrals. Two of them have 4 crimps.

I'm guessing this is 4 runs of 500kcmil? If they used 500kcmil versa crimp lugs they're wrong. They have a range of 550-600kcmil compact strand aluminum when using a died crimper.

 

[ptonsparky]

Looks like PP crimps from here.

 

[tortuga]

What was the brand of compression lugs used? And what crimper?

 

[infinity]

Everything points to the improper installation of those terminals. It is odd that one conductor got so much hotter than the others. Did anyone measure the load just for the hell of it?

 

[GoldDigger]

Everything points to the improper installation of those terminals. It is odd that one conductor got so much hotter than the others. Did anyone measure the load just for the hell of it?

Unbalanced load is certainly one explanation. But a poorly crimped connection can have a range of excess resistance rather than a specific value and this may just be a statistical worst case.
Once the temperature gets high enough it could then cause the resistance to increase, leading to a feedback situation.
If the parallel conductor set (assuming that is what it is) is long enough, the current through the one conductor will not be reduced much by the higher resistance, so that may not be a factor.

 

[ramsy]

Parallel sets are subject to overheating without identical characteristics
* Look at the brown phases at top of photo
* Insulation is vaporized off 1 conductor only
* Follow that conductor down into the spaghetti mess
* See it take off in a different direction
* If passing thru metal by itself, 300.20(B) inductive heating may also be a cause

 

[electrofelon]

While it does look like they need more crimps, I would try to do 4 barring any specific instructions, I am skeptical that these would melt down due to 1 or 2 few crimps.

 

[ppsh]

While it does look like they need more crimps, I would try to do 4 barring any specific instructions, I am skeptical that these would melt down due to 1 or 2 few crimps.

I would say 4 crimps would be the absolute minimum to those lugs, and they crimped once at each end of the allowable crimp area. Nothing in the middle. Attached a photo of 500kcmil AL lug properly crimped with a 12ton crimper. If they didn't strip quite the entire length, the crimp closest to the tang won't do anything.

 

[petersonra]

Improper termination or parallel conductors that are not the same length.

 

[wwhitney]

parallel conductors that are not the same length.

Surely that would only show heat damage on the shorter conductors, rather than all of them?

Cheers, Wayne

 

[LarryFine]

Surely that would only show heat damage on the shorter conductors, rather than all of them?

It could show up on the connectors with less resistance if the current was high enough.

And don't call him Shirley.

 

[ppsh]

Surely that would only show heat damage on the shorter conductors, rather than all of them?

Cheers, Wayne

I would think so. The biggest clue here is that they are overheating at the termination. Wires start looking fine a few feet down. If it was a issue of unequal length causing overheating, I would expect to see it over the length of the wire.

Even if it was an imbalance issue, assuming it's 4 sets of 500al for 1200a. They are likely 90c crimp lugs bolted to busbar. 500al is 350a at 90c.

 

[wwhitney]

It could show up on the connectors with less resistance if the current was high enough.

Right, which are the shorter conductors for parallel conductors of the same size.

Cheers, Wayne

 

[rambojoe]

Alright... Its not too clear on my phone but-
- either theres only 3 yellow or three brown.
- look left on the yellow buss. Appears brown was rubbing buss.
- i dont know why but i hate lugs so close.
- this gear looks modified.
- How come some busses appear to be connected?!
- i say dead short, brown cable to yellow buss.
I just stared at the photo for 5mins! If im wrong, let me know...

 

[rambojoe]

And heat discolor on orange buss after fender- heading to the (i hope) mcb or mcc

 

[LarryFine]

I think some local fall-of-potential testing while under load is called for.

I just stared at the photo for 5mins! If im wrong, let me know...

No, you're right. You did stare at it for five minutes.

 

[petersonra]

Surely that would only show heat damage on the shorter conductors, rather than all of them?

Cheers, Wayne

If the termination is getting hot because the conductor is overloading it could be overheating near the termination of unaffected conductors

I think checking the length would be my first attempt. It looks like the terminal is crimped on ok and the tightening torque is reported as ok, so you are not left with many options.

Get a milliohms meter and measure the resistance of each conductor. Admittedly, this requires some skill and technique that most electricians won't have but it is not something unlearnable. If necessary, hire it done.

Otherwise you have just guessing.

Another option is to measure the current in each individual conductor under load. Something any real electrician can do.