Voltage Drop Calcs for Panel's with possible future load.

[theophilus88]

Currently I am working on a project for a fruit and nut processing facility. The owner has asked me to provide panels with some extra space for future capacity. For instance, I have a 480V, 600A panel with only 300A's of demand load on it. When calculating for voltage drop on a panel like this, how would you size the feeder? I would do my normal 3% calculation to make sure we are meeting the correct voltage drop, but I'm struggling on what amperage to use? Would we base it on panel's full size of 600A's? It seems highly unlikely that we would ever reach the full capacity of 600A's and the feeder size would be enormous considering my panel is almost 800A's away. Thoughts?

 

[winnie]

If you are at 480V you go pretty far before voltage drop changes your conductor size from the minimum required by ampacity.

Consider: a 600A circuit would require 2x 350kCmil or 3x 3/0 conductors on ampacity alone.
2x350 kCmil gets you 510 feet before you need to upsize for voltage drop at the full 600A
3x3/0 gets you 460 feet.

If your customer wants a 600A panel with room for future expansion, then I'd price out the cost of a 600A feeder (no VD consideration) and one with voltage drop at 80% load calculated.

-Jon

 

[Russs57]

Maybe give him two sets of 350 and option of adding a third conduit now if it would be difficult/costly/impossible later.

 

[Dennis Alwon]

How far away is the panel from the service?

 

[theophilus88]

If you are at 480V you go pretty far before voltage drop changes your conductor size from the minimum required by ampacity.

Consider: a 600A circuit would require 2x 350kCmil or 3x 3/0 conductors on ampacity alone.
2x350 kCmil gets you 510 feet before you need to upsize for voltage drop at the full 600A
3x3/0 gets you 460 feet.

If your customer wants a 600A panel with room for future expansion, then I'd price out the cost of a 600A feeder (no VD consideration) and one with voltage drop at 80% load calculated.

-Jon

I just ended up taking 80% of the Main and sizing my feeders based on that since this is what the breaker is usually rated to trip at. I figured we probably don't want much load past 480A's.

 

[electrofelon]

I just ended up taking 80% of the Main and sizing my feeders based on that since this is what the breaker is usually rated to trip at. I figured we probably don't want much load past 480A's.

Personally, I would consider that too conservative. It depends on the situation and specifics of course, but I would probably use 1/2 to 2/3 of the feeder rating for VD purposes.