Amperage for a balanced 277 volt load on 480 volt 3 phase

[RJ_Heater]

I'm working on a project, where the incoming voltage is 480 volt 3 phase 4 wire.
We are going to run (9) 277 volt single phase heaters and balance them over the 3 phase power.
Total wattage is 27,195 watts. each 277 volt circuit will pull 10.9 amps roughly.
How do I determine the actual load amps for the 480 volt incoming breaker?
In the past I've used the 277 volt amps actually on each leg, (or in this case roughly 33 amps) and added 25% but there should be a formula for the total load amperage.

 

[ptonsparky]

(27195/480)/1.73=32.749 *1.25=40.9

 

[kwired]

Note that formula is only accurate with balanced load, if you only had 8 heaters but still as balanced as possible then one line would be drawing less then the others, and there would be neutral current where with 9 heaters neutral current would only amount to what is caused by minor differences in resistances/input voltages.

 

[rbauerff]

Refer to NEC 210.4

Refer to NEC 210.4

You have a multiwire circuit. All your loads must be line to neutral (277 volt), you must have a circuit breaker that opens all phases at the same time (3 pole). Each phase is taken separately so they do not need to be balanced. The phase with the highest ampere will determine your wire and breaker size. If each heater is 10.9 amps and the most heaters on a phase 3, you need 32.7 X 1.25 or 41 amps. There are some code exceptions and particulars that might apply to your situation that you will want to check out.

 

[kwired]

You have a multiwire circuit. All your loads must be line to neutral (277 volt), you must have a circuit breaker that opens all phases at the same time (3 pole). Each phase is taken separately so they do not need to be balanced. The phase with the highest ampere will determine your wire and breaker size. If each heater is 10.9 amps and the most heaters on a phase 3, you need 32.7 X 1.25 or 41 amps. There are some code exceptions and particulars that might apply to your situation that you will want to check out.

single pole breakers with handle ties is acceptable.

You are correct that the phases do not need to be balanced, usually good design to try to balance loads as best as possible though.