Unexplained heating on feeder conductors

[rambojoe]

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


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

Gee thanks... Are there missing parallels? The pic download is crappy

 

[LarryFine]

Gee thanks... Are there missing parallels? The pic download is crappy

Now that I figured out what you are saying, yes, it looks like the most-damaged brown has burnt open.

That yellow is bare for a ways, but it looks like a several inches of that brown is missing.

 

[Tulsa Electrician]

I would like to add there should be an embossed identification on the lugs on the crimped wires. Depending on connector and brand the correct crimping for the conductor type is important. Most marked on connector based on conductor type. An example would be copper two crimp between bands and three crimps on band for Al. You need to know what connectors were used and the crimping requirements for those connectors. And follow the instructions.

Either way a die identifier would be embossed for each crimp on the connector. Unless some generic crimper was used.

I am leaning toward improper crimps my self for now.

Need load information etc.

No matter what it got hot.
Surprised no one said anything about the size of the egc. Looks a little small for a feeder or 1200 amp.

 

[ptonsparky]

I've measured the difference of parallel conductors that were trimmed by the POCO at the pole top. 5-10 amps. Just how much difference in length would be needed to create so much heat?

 

[jim dungar]

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...

Probably an obstacle illusion. I think there are two conductors, brown and yellow, with their insulation burned off which are in line with each other.

 

[rambojoe]

Probably an obstacle illusion. I think there are two conductors, brown and yellow, with their insulation burned off which are in line with each other.

Thx. Slightly out of line but something (or two) is obscured...
I was trying to count cables outta the pipes.
Appriciate the 2nd eyes.

 

[ramsy]

Alright... Its not too clear on my phone but-
- either theres only 3 yellow or three brown.

Counting 5 Brown conductors at bottom of picture.

Did not notice before that Yellow changes color to Orange, then Brown, just before insulation burns off.

- 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.

This picture causes more questions than it solves.

 

[rambojoe]

Counting 5 Brown conductors at bottom of picture.

Did not notice before that Yellow changes color to Orange, then Brown, just before insulation burns off.

This picture causes more questions than it solves.

As much as it disgusts me i sure wish i inspected the aftermath...
Questions are good when we head into work. Sure seems like small Al for 1200a, dont it...
Some cable markings are visable to a point.
Did S. One sub cu size cable for Al?
Disgusting.
Anyway, would be nice to hear from the o.p.
1200a is pentagon/amazon distr. sized!

 

[ramsy]

Sure seems like small Al for 1200a, dont it...

My mistake, using single phase rather than 3 phase, which only requires 4/0 x 4 for cable

 

[ramsy]

Sure seems like small Al for 1200a, dont it...

Termination temperature is a different story.

Can someone check my temperature calc, for 3 phase.
Does it really take #300.AL x 4, to keep 1200A within 75°C column?

 

[electrofelon]

Termination temperature is a different story.

Can someone check my temperature calc, for 3 phase.
Does it really take #300.AL x 4, to keep 1200A within 75°C column?

300 AL is 230A, x 4 =920.

 

[GoldDigger]

Now that I figured out what you are saying, yes, it looks like the most-damaged brown has burnt open.

That yellow is bare for a ways, but it looks like a several inches of that brown is missing.

Looking at it close up, it appears to me that any open appearance is an illusion caused by the fragments of insulation that have burned completely black, The wire strands show no signs of melting.

 

[ramsy]

300 AL is 230A, x 4 =920.

230A x 1.732 = 398A x 4

 

[don_resqcapt19]

I've measured the difference of parallel conductors that were trimmed by the POCO at the pole top. 5-10 amps. Just how much difference in length would be needed to create so much heat?

It would take a lot of difference in length to make any real difference assuming that the length is the only difference.
If you have a 2000 amp circuit using 5 sets of conductors and 4 of the sets are 50' and the last set is 55'.
The four 50' lengths would carry 407 amps and the 55' one would carry 370 amps. If I make the long on 60' it would carry 345 amps and the four 50' ones would carry 414 amps.

It really is based on the percentage difference in lengths, and there is much more impact where the run is short.
if I have the same 2000 amp circuit with five sets having the lengths of 20', 22', 24' 26' and 28' the currents would be 473, 430, 394, 364 and 338.

(note the numbers have been rounded so they will not total exactly 2000 amps)

 

[ptonsparky]

Even such, those conductors would need to be at the full 2000 +-, for an extended period of time. Unlikely.

 

[petersonra]

Has anyone looked at the other end of these parallel cables to make sure they really are parallel?

 

[winnie]

Termination temperature is a different story.

Can someone check my temperature calc, for 3 phase.
Does it really take #300.AL x 4, to keep 1200A within 75°C column?

If you actually need the full 1200A, and have 4 aluminum conductors in parallel, then you need at least #500 kcmil to conductors in the 75C column.

-Jonathan

 

[electrofelon]

230A x 1.732 = 398A x 4

I guess I dont understand what you are calculating here.

 

[wwhitney]

230A x 1.732 = 398A x 4

That doesn't work. The sqrt(3) factor in a 3 phase power formula is related to the relative voltages. Current is still current.

So no sqrt(3) factor when working with currents that are in phase.

Cheers, Wayne

 

[ramsy]

you need at least #500 kcmil to conductors in the 75C column

Thank you for that clarification