If I follow the code 800 DC amp feeders

[matthewvav]

I presently have a 500 hp DC motor that is using two 500 AWG THHN wires for A1 and A2. All four wires are ran in a three inch conduit and it presently does not meet code. At the present code specifications I need 125% of full load current for the motor leads or 1000 amps.
If I follow the code I would have to run 3 350AWG in two conduits to meet the requirements. I have another 500 DC motor that was engineered from an outside electrical engineering firm and they used two 500AWG in seperate conduits. Are my calculations wrong? My continuous current is 700 amps with the possibility of going past 800 if the equipment is stalled. I would appreciate any help.

 

[Dennis Alwon]

If you are saying that the motor with 125% is rated 700 amps then 2- pair of 500 copper is sufficient. What is the nameplate on the motor?

If you are using one conduit then de-rating must be applied when more than 3 conductors are in the conduit.

 

[petersonra]

I presently have a 500 hp DC motor that is using two 500 AWG THHN wires for A1 and A2. All four wires are ran in a three inch conduit and it presently does not meet code. At the present code specifications I need 125% of full load current for the motor leads or 1000 amps.
If I follow the code I would have to run 3 350AWG in two conduits to meet the requirements. I have another 500 DC motor that was engineered from an outside electrical engineering firm and they used two 500AWG in seperate conduits. Are my calculations wrong? My continuous current is 700 amps with the possibility of going past 800 if the equipment is stalled. I would appreciate any help.

I would not be worried about the stall current. If the FLA is 700A, you need 875A worth of conductors. (2) 500 AWG does not give you that IMO.

I agree that you need (3) 350.

Having said that, for whatever reason, it seems pretty common for people to cheat on wire size for large DC motors.