120/208 to 277/480

[mstrlucky74]

Have a current size feeder based on 120/208 load. I'd like to distribute 277/280 then step down and feed panel. How do I determine amperage/feeder needed for the transformer.....this conversion? Thank.

 

[ActionDave]

Amps and volts go up and down all over the world but kva is kva. You need as many kva's at 480V as you do at 208V.

 

[Carultch]

Have a current size feeder based on 120/208 load. I'd like to distribute 277/280 then step down and feed panel. How do I determine amperage/feeder needed for the transformer.....this conversion? Thank.

Think of a transformer like a gear system for electrical power.

A mechanical gear system trades rotation speed for torque, while (nearly) preserving the power transmission rate. The product of torque and speed is the same on both sides of an ideal gear.

A transformer trades voltage for current, while (nearly) preserving the power transmission rate. The product of voltage and current is the same on both sides of an ideal transformer. Assume it is an ideal transformer, for purposes of circuit sizing.

 

[kwired]

Also keep in mind that just because you currently have say a 200 amp @208 volts (x 1.72) = ~72kVA feeder, does not necessarily mean you have a 72 kVA load. If load is only 39 kVA, they may have simply allowed for future load, but you possibly could get by with a 45kVA transformer though you would have less future load capabilities.