ECN Forum Forums General Topics of the Trade General Discussion Area 3 Phase 480 parallel runs.....

I've posted about this before, but a new twist.

Spec'd out; pipe on site, ready to dig and bury. Customer wants to increase amperage - future capacity. Loads are all motors - 2 soft start.

Spec'd at 1290A - 3 parallel 4" RMC runs, each containg A,B,C,N,G - 500 MCM Cu + 1 3/0 G.

He now wants 1600A. My solution: 4th pipe run - give me 1720A; he wants to add wire to the planned 3 runs.

Fill factor is ok to add 4th wire, but it would lead to A,A,B,C,N in pipe 1, A,B,B,C,N in pipe 2 and so on. I was always taught (in RMC)to keep A,B,C,N together in each pipe, or you end up with a "shorted turn" effect due to any imbalance, and heat up the pipe.

All I can find in a first look is Article 300.20 - "all phase conductors shall be grouped together".

Advice? Comments? Analysis? Pointers?

Thanks!