jatindall82
Member
- Location
- troup, texas
What size branch circuit overcurrent protection device and conductor (THHN) is required for a 19kva of non linear loads (75 degree terminals). The branch circuit is supplied by a 208/120v, 4 wire, 3 phase, wye connected system.
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 the #4 THHN.
The instruction at this point say use the 90 degree column for the ampacity and then correct it at 80%
My question is why am I using the 90 column at this point?
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 the #4 THHN.
The instruction at this point say use the 90 degree column for the ampacity and then correct it at 80%
My question is why am I using the 90 column at this point?