Feeder Sizes

[mstrlucky74]

I assume the (2) sets of 4/0 are being sized based on then125hp and not the 2000A switch because those feeders would not be enough. So if I wanted to size from the 600a FP switchto the 45kva I need I need to size based on the switch or transformer size. It?sGRC w/THHN. Thanks

 

[Dennis Alwon]

Look at Table 310.15(B)(16)-- I assume you want 2 runs for the 600 amp so find the wire based on 75C that is good for 300 amps and then parallel it.

 

[infinity]

For the transformers you need to look at 695.5.

For the 125 HP fire pump the conductors are sized at 125% of the pump motor FLA from T430.250. At 208 volts that would be 343 amps so the conductor minimum size would be 343 * 125% = 429 amps. That means two sets of #4/0 (225 amps/set) would be compliant. The 2000 amp switch and 2000 amp OCPD are sized for the locker rotor current of the fire pump motor and are typically about 6X the fire pump FLA.