Temporary Service Drop

[Red Wiggler]

When calculating conductor size for a temporary "overhead" service drop, do you need to derate the conductors if the they are installed in a pipe? (3 phase 4 wire 480 volt service)

For instance I need to supply a 480 volt 400 amp temp service. I had considered using two risers (2 1/2") containing 4 - 4/0 copper THHN with a #2 copper ground.

Is the 4/0 too small because of derating? (4 current carring conductors in a pipe 80%)

Or should I go to 4 - 250 Kcmil copper?

 

[LarryFine]

Is the 4/0 too small because of derating? (4 current carring conductors in a pipe 80%)

Why is there a fourth wire? What makes the fourth wire a CCC?

 

[Red Wiggler]

The neutral. Our Utility provides a neutral with the service drop to their Transocket.

 

[LarryFine]

The neutral. Our Utility provides a neutral with the service drop to their Transocket.

That neutral need not be counted toward ampacity derating, but must be counted for conduit fill.

The neutral must be run to the main disconnect, and be bonded to EGC's and GEC's there.

It need not be as large as the line conductors. It can be sized as an EGC if there is no neutral load.

You should not run a separate EGC on the line side of the main disco; the neutral does that.