calcuation question need help with

[jatindall82]

What size branch circuit overcurrent protection device and conductor (THHN) is required for a 19kva of nonlinear loads (75 degree terminals). The branch circuit is supplied by a 208/120v, 4 wire, 3 phase, Wye connected system.

Could someone help me work through this calculation PLEASE!?

 

[Dennis Alwon]

What size branch circuit overcurrent protection device and conductor (THHN) is required for a 19kva of nonlinear loads (75 degree terminals). The branch circuit is supplied by a 208/120v, 4 wire, 3 phase, Wye connected system.

Could someone help me work through this calculation PLEASE!?

How about show us what you have tried. I assume this is homework and we prefer you give it a go first. Also is the load continuous

 

[ptonsparky]

That is a big branch circuit.

What else can you tell us about your install?

 

[jatindall82]

test question

test question

That's a sample question for branch circuit continuous loads

 

[jatindall82]

what i have come up with

what i have come up with

I converted the kva to amps

va / (volts x 1.732)
19,000 /(208 x 1.732) = 52.74 amps rounded to 53 amps

branch circuit OCP has to be sized @ 125% of the 53 amps
53 x 1.25 = 66.25 = 66 amps. So a 70 amp OCP

To select the conductor I believe I have to increase 125% also.

66 amps in the 75 degree column requires #4 @ 85 amps

Since there are more than 3 current carrying conductors in the race way I have to correct it.

Do Increase it by 80%???