125 Amp Sub Panel Wire Size

[millwoodva]

Subpanel install in a pole building. House is wired for 400 amp service..
180' total... (80' from main panel to house wall exit.. underground feed 100' to pole bdg)
planning on aluminim conductors... Thinking continuous run of 2/0-2/0-2/0-1.
Though if 3 ea. 1/0 will carry the load that distance.. prefer that less expensive route..

 

[Dennis Alwon]

What is the load on the building? You cannot do a voltage drop calc without knowing the amperage. If you go for the 125 amp load than 2/0 would be correct

BTW, welcome to the forum

 

[infinity]

#1/0 will work for 90 amps, as Dennis pointed out in the worst case scenario #2/0 would work.

 

[JFletcher]

Welcome to the forum.

#1/0 will work for 90 amps, as Dennis pointed out in the worst case scenario #2/0 would work.

Why wouldnt #2 work for 90A?

~~~~~~~~~~~~~~~~~~~~~

Also, you may be able to find already cut lengths on ebay for cheaper than the supply houses.

 

[ActionDave]

Why wouldnt #2 work for 90A?

It would work fine and would be what I would use.

 

[infinity]

Welcome to the forum.



Why wouldn't #2 work for 90A?

125 amps, minimum Al conductor size is #1/0.

 

[JFletcher]

125 amps, minimum Al conductor size is #1/0.

If the 125A subpanel were fed from a 90A breaker at the main panel, and the calculated load was <90A, then #2 Al could be used, yes?

 

[infinity]

If the 125A subpanel were fed from a 90A breaker at the main panel, and the calculated load was <90A, then #2 Al could be used, yes?

Sure but there is nothing in the OP that suggests that they want to use less than a 125 amp OCPD. The minimum permitted conductor would be #1/0 Al with a 125 OCPD. At 90 amps of load your voltage drop would still be under the 3% recommended threshold. As Dennis stated if you wanted the full 125 amps then with the 3% maximum recommended VD you would need to go up to #2/0.