Bjenks
Senior Member
- Location
- East Coast of FL
I am looking at the calculations example in the 2008 and 2011 NEC handbook of NEC 430.110. First it says the minimum ampere rating of the disconnecting means is 61.3A (1.15 x 53.3A) which I agree with. Then looking up the LRC of 220.1A it says you need 15HP. Then it says that the 15HP fails to meet the minimum current requirement of 61.3A which I agree. It says to go to the next size up of 20HP which obviously meets the 220.1A LRC and able to handle the full load rating of 53.3A. But that seems to contradict the 61.3A requirement as the 20HP 230V motor is 54A. It seems to me based on the example you would be required to use a minimum 25HP disconnect in order to handle 61.3A. In the real world, I would have used a SQ D 100A disconnect rated at 40HP, but according to their example I could have used a 60A disconnect rated at 20HP based on 3 phase 240V.