feeder wire size

[jonshoemaker]

I have calculated the load on a sub panel and I am wodering if the "high leg" ungrounded feeder wire can be a smaller size than L1 and L3.

The load on L1 is 123 amps, L2 is 53 amps, L3 is 123 amps. This is a 120/240 four wire delta system.

The load calculation program that I used to obtain these values recommended #1/0 THHN Cu for L1 and L3 and
# 6 THHN Cu for L2, neutral, and ground.

Any comments will be greatly appreciated.

 

[Dennis Alwon]

What size breaker will you use then?????

 

[Dennis Alwon]

You see the problem?

 

[celtic]

The load calculation program that I used to obtain these values....

What program was that?

 

[LarryFine]

I have calculated the load on a sub panel and I am wodering if the "high leg" ungrounded feeder wire can be a smaller size than L1 and L3.

The direct answer is yes, it is permissable, but, as the other responses have pointed out, you must still protect each conductor at its ampacity.

The simplest way to do this is to find a 125/60/125a 3-pole breaker; otherwise, separate the 1-phase and 3-phase loads into separate sub-panels.

You might actually run the 3-phase load directly from the main panel, and make the sub-panel 240/120v 1-phase only, for the single-phase loads.

 

[augie47]

breaker

breaker

I have seen breakers on OEM equioment with different ratings per pole. I have also tried to purchase them from electrical distributors and am told there is no such animal (except OEM). Have you ever been able to purchase one, and if so, what brand ?

 

[iwire]

Install a 3 pole fused disconnect switch and be done with it. :smile:

 

[jonshoemaker]

feeder wire size

The load calculations that I obtained are from this program.
"Panel 2003 (Ver 3.0)" - Copyright Durand & Associates
My thought also was how could I protect the 60 amp wire size on the L2 leg with a 125 amp CB.

Thanks for the input.