Single Phase Load Calculation with 3 Phase Service

[ecampos]

How is the FLA of single phase components calculated when the service is 3 phase? For example with a 480V/3PH service, loads being a 3kW electric heater @ 480V/3PH, and a 1KVA transformer @ 480V/1PH.

Would the total panel FLA be:
( 3000 / (480 * 1.73) ) + ( 1000 / (480 * 1.73) ) = 4.8?
- or -
( 3000 / (480 * 1.73) ) + ( 1000 / 480 ) = 5.7?

 

[Eddie702]

3000/480= the single phase amps of the heater. Divide the answer by 1.73 to get the 3 phase amps=6.25/1.73=3.6 amps

1kva transformer=1000/480=2.08 amps

3.6A + 2.08A= 5.7A

So you would have 5.7A on two legs of the 480 and 3.6 amps on the other leg if thing are fully loaded