Mocp

[lmchenry]

Here is the scene. 120/208 3-phase 200 amp service. 4/0 al conductors from service disconnect/overcurrent device to mlo panel 100' away. Serves aprroximately 20 circuits and has a load of about 120 amps. Does the 4/0 conductors and the MOPD correspond by using 240.4b?

 

[raider1]

Yes, 4/0 aluminum conductors have an ampacity of 180 amps at 75 degrees C. Because the load is less than 180 amps you can use 240.4(B) to use the next size up rule and protect the feeder with the next higher standard breaker.

Chris