Air curtain sizing branch circuit & OCPD

[cppoly]

Does this look correct for the branch circuit wiring and OCPD for an air curtain with (1) 20 kW heater @ three phase, 208V + (2) motors @ single phase, 208V, FLA 3.6 amps each.

Branch circuit conductors:

20 kW / 360 = 55.6 A
3.6 x 1.25 = 4.5 A
3.6 x 1.00 = 3.6 A

Conductors = 63.7 = MCA

OCPD (circuit breaker):

55.6 + 3.6 x 2.5 + 3.6 = 68.2 = 70 A C.B.??

 

[Flex]

where you get the 360 from?

 

[cppoly]

Do you mean the 3.6?

The datasheet says 208/230V and lists 3.6 A, even though it should be 3.2 according to the NEC table.

Just reread it. The 360 came from 208 * 1.732

 

[david luchini]

Does this look correct for the branch circuit wiring and OCPD for an air curtain with (1) 20 kW heater @ three phase, 208V + (2) motors @ single phase, 208V, FLA 3.6 amps each.

Branch circuit conductors:

20 kW / 360 = 55.6 A
3.6 x 1.25 = 4.5 A
3.6 x 1.00 = 3.6 A

Conductors = 63.7 = MCA

OCPD (circuit breaker):

55.6 + 3.6 x 2.5 + 3.6 = 68.2 = 70 A C.B.??

I don't think a 70A branch circuit breaker will provide proper for a 1/4HP 208V single phase motor.

If the calculation was for a motor feeder, (or a branch circuit in accordance with 430.52(C)) the calculation would actually be 55.6 + 3.6 + 15 =74.2 => which is an allowable 70A c/b. (sized down, not next size up.) The 15 is the allowable ocpd size for one of the motors.