ECN Forum Forums Code Related Discussion NEC & other Code issues 2 power sources in one building?

I got a call to give an estimate to run a 240 volt line to a detached utility building. The homeowner has already run a 120 volt line to the building and terminated it in a 6 circuit panel. He wants me to run another line from his house and terminate it in another panel so he can run a 240 volt air compressor. One of the exceptions for this according to a old code book ( don't have a new one yet) if there are diffences in voltages this would be allowed. Could 120 volts verses 120/240 volts, be used in this exception, justifying another feeder??

The short answer is no. They are both 120/240 1p

What if you just size the new feeder to cover the existing and new loads? Maybe you can reuse the existing breakers and perhaps even the panel.

The 'different voltages' you are thinking of are for when the power is from different systems. For example, when the shop has both a 480/277 and 120/240 service.

The customer needs to realize that his lack of foresight yesterday does not mean you get to save his tail by tossing out the book today. Thee's no way to avoid disconnecting the old feed, and digging for the new. While you're at it, don't forget the outside disconnect.

Perhaps this time he'll let you bury some big pipe(s), rather than just slipping a little romex under the sod (OK, I assume much - but we've all seen this before).

I say "pipe(s)" because this is a very good time to run a second pipe -preferably 1"- for future phone / computer / CATV / alarm service. As long as the ditch is dug - what's the cost of a little PVC?

I also hope the building has a proper ground rod (or GE). He already needs one - the panel makes the wire he has a feeder, not a branch circuit.

Thanks for the reply. I guess I really knew that. I was hoping maybe there was a loop hole I was missing. And yes I will recommend to the homeowner that we just pull a new feeder to take care of both panels. He'll probably not want me to do it and do himself illegally, but that will probably be the best anyway. Too much liability involved.

For the record the code reference is Article 225 Section 225.30. And the answer is only one supply to the building with a few exceptions.

All the money is in the trench -- not the pipe.

Always oversize U/G pipes. If the conductors need 3/4" EMT -- go with 1" PVC if not 1.25" PVC. It's dirty down there.

Add a spare -- every time.

NEVER use PVC under 1" unless it is a trivial short hop for a hot and a neutral.

Because all the money is in the trench -- not the pipe.

As CAT standards keep ramping up -- the larger the sweep must be.

Just another reason to shun small diameter underground runs.