Sub Panel miminum size?

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chevyx92

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I had a conversation with co-worker about his plan to install two sub panels in apartment buildings and he mentioned one panel would be fed with a 2 pole 30 amp breaker and the other a 2 pole 40 amp breaker.....the loads to be served are different. I mentioned that I believed that he would have to run no less than a 60 amp feeder but I can't seem to find it in the code. Am I out in left field here or can you feed a sub panel with any size circuit you want? I for some reason thought there was something saying it had to be 60 Amp minimum. Any advice will be greatly appreciated.
 
I think each dwelling unit has to have a feeder sized for 60A. I don't think there is any requirement that the main in the PB be sized that way. In other words, I think you have to run wires big enough to handle 60A to the PB, but the main in the PB can be smaller.

Note use of phrase "I think".

However, if this subpanel is being fed from a PB already designated for this aprtment, I think he can do whatever he wants.
 
I do not know of any minimum size for a feeder within a building. If the feeder goes to a separate structure then you may look at 225.39 for disconnect size
 
Dennis Alwon said:
I do not know of any minimum size for a feeder within a building. If the feeder goes to a separate structure then you may look at 225.39 for disconnect size
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I think thats what I was thinking about but thats for outside separate structure disconecting means, I guess I was confused . Thanks.
 
Dennis Alwon said:
I do not know of any minimum size for a feeder within a building. If the feeder goes to a separate structure then you may look at 225.39 for disconnect size
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The way that I read that, without commas between the terms, all that is say is that the disconnect needs to be rated for 60 amps. I don't believe it means that the feed or the subpanel needs to be 60 amp.
 
Rick Christopherson said:
The way that I read that, without commas between the terms, all that is say is that the disconnect needs to be rated for 60 amps. I don't believe it means that the feed or the subpanel needs to be 60 amp.
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I think that is what I stated-- look at my last words-- 225.39 for disconnect size
 
How about a potential real life example.

Lets say main panel is an old pushmatic panel in a dwelling, I want to add 2 new 15 amp 120 volt branch circuits that also require AFCI protection in recent NEC editions. You are not going to find an AFCI breaker to put in the pusmatic panel. Lets say you put in a 2 pole 15 amp breaker to serve as a feeder for a newer panel that you can easily obtain AFCI breakers for. This feeder could be just a couple feet long and the sub next to the pushmatic, or it could be a couple hundred feet long - it is still a 15 amp feeder either way and perfectly allowable as the load on the feeder is no more than 15 amps. It would not be allowed to supply another structure unless a 15 amp feeder was allowable for that particular structure - which would pretty much only be allowed in cases where the separate structure contains a single load.
 
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