Heating and induction on cables bunched together.

[mull982]

Relating to the same circuits for another post I have, there are two different circuits each having (6) sets of parallel 500MCM per phase. This is a mining application where I have switchgear on a portable skid down in a quarry. The cable that I am using is a 3/c type GGC cable. Because of the tight quarters on the skid all 12 of these cables are bundled up and laying pretty much right on top of each other. They are in free air just laying in the bottom of the skid.

Is there anything that I should be concerned about by having these cables bunched together laying on top of one another. Should I be concerned about mutual heating from all of the other conductors in this situation.

Because of the fact that there are 2 different circuits ( 6 500MCM each circuit) that are bunched together should I be concenred about mutual induction between the two circuits. Both the circuits are 480V circuits with one carryrying a slightly larger amperage load than the other. The circuits are only run next to each other for about 10ft.

 

[RayS]

no. as long as the phase conductors are bundled together,(ABC, ABC,... not AAA, BBB,...) there should be no issue.

How do you move cables like that?

 

[don_resqcapt19]

If all of the cables are laying on each other and are close to full load you can expect to have excessive heat and possible cable damage. Under these conditions the cables need to be derated per 310.15(B)(2)(a).
Don

 

[Pierre C Belarge]

If all of the cables are laying on each other and are close to full load you can expect to have excessive heat and possible cable damage. Under these conditions the cables need to be derated per 310.15(B)(2)(a).
Don

As Don has mentioned ampacity adjustment will be necessary. Take a look at the very last sentence of 310.4 - p. 134 of '05 & '02

 

[iwire]

This is a mining application where I have switchgear on a portable skid down in a quarry.

The NEC might not even apply to this.

Check out 90.2(B)(2) to be sure.

 

[e57]

bundled up and laying pretty much right on top of each other. They are in free air just laying in the bottom of the skid.

Anyway why not rack them as single conductors in a single layer a little more than one cable diameter apart as ABC - ABC? Then treat it as a cable tray and select ampacity according to 392.11(B). (Maybe weld a few 2x2" sq tube guards in place too.... Not that I know much about mine environments but some type of guarding is not a bad idea. And are you even required to stick to the NEC?) Anyway, I think you could escape de-rating completely, and use table 310.17 this way.


Wait - just re-read your post -

"The cable that I am using is a 3/c type GGC cable."

Same thing (kinda) cables in a tray using 392.11(A)

 

[charlie b]

Mutual heating will likely be a problem. I agree with Don?s statement on this issue. But mutual induction will not be a problem. Within and single cable, you have all three phases. The magnetic fields generated within the three phase conductors will essentially cancel out each other out. So no cable will impose a net magnetic field on any other.