power at exterior of remote building, but not supplying

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royta

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A homeowner has an air compressor he would like installed on the backside of a remote building near his house. I will install an 8x8x4 can containing a relay, with the relay control switch located in the garage. There is already a 50A 240V circuit running to the building, but it is supplying the AC unit, and not the building itself. There are no electrical items associated with the remote building whatsoever. There is no room for another breaker in the main panel, so running a second circuit to the air compressor is not an option, at least not from the main panel itself. I'm trying to do this as economical as possible for the homeowner, and obviously meet code at the same time.

Should I:
A) Turn the 50A AC circuit into a sub-panel feed with sub-panel located on exterior of remote building and drive a ground rod?

B) Turn the 50A AC circuit into a sub-panel feed with sub-panel located immedietely to the left or right of main panel. Install one conduit, containing two circuits, to junction box located on exterior of remote building. Branch out to disconnects for each unit. Wait, wouldn't I still need a ground rod, as the Exception to 250.32(A) would not apply, would it?

Is there a scenario where I won't have to drive a ground rod?

Thanks.

[ November 16, 2004, 11:49 AM: Message edited by: royta ]
 
Re: power at exterior of remote building, but not supplying

What size and type of wire is the ac unit being served with? Is there a neutral conductor-sure there isn't but have to ask? Also, did they run the sub-feed in conduit the entire way? In addition: How far away is this remote building. Is this remote building a garage? Why have an exterior non-service rated panel? How big is the building? What's the ampacity of the compressor? Does the customer plan to use the compressor inside the building?

Sorry sooooooooo many questions!

[ November 17, 2004, 01:23 AM: Message edited by: resistance ]
 
Re: power at exterior of remote building, but not supplying

I believe it had AL 6-3 SE Type R installed in a 3/4" conduit. No, I didn't do the original install. The building, not a garage, is located within 10 or so feet of the side of the house. It's been a couple months, so I'll need to check things out again. I believe the building was less than 100 square feet. The compressor, which I seem to have forgotten the rating, will be located outside the building, right next to the AC condensor unit. I don't know if there is electrical in the building or not, but if there is, it isn't from the AC circuit, as the existing feed is used solely for the AC unit.

I need to somehow get power to the air compressor, but as I said before, the panel is full. So, a sub-panel, or tapping the AC circuit (if legal??), is my only option.
 
Re: power at exterior of remote building, but not supplying

We need to find out if they want to keep the AC unit. If they do, then what is the name plate rating? (Hopefully they don't!)

We will also need to know the name plate rating of the new load (Compressor).

Both above answers will give us an idea on what we need to do next. Right now, I can see us doing a demand load calculation.

Make note: If the DLC checks out to accept both units, you can use a quad breaker, and come off that OCPD with the required subfeed. You would then run that subfeed underground to the desired location. Make note that NEC rules will play a role in running feed and installing all equipment--if this is an option.

They have many other options, but lets get the answers for the above questions I ask.

The tap rule (tapping off the AC): I will find out if you can do what you ask.

[ November 18, 2004, 01:17 AM: Message edited by: resistance ]
 
Re: power at exterior of remote building, but not supplying

It would be no problem if they didn't need the AC condensor unit, but unfortunately, they do. If I tap off the AC disconnect, I'd need a fusible disconnect for the air compressor, which makes it a feeder, necessating a ground rod because it is a seperate structure. The panel is completely maxed out. A quad won't work without modifying something. I think my only alternative is a small sub-panel, either mounted on the side of the house, or on the side of the small remote building.
 
Re: power at exterior of remote building, but not supplying

Sounds like you have a hand on the situation. Make note that even if you plan on running a non-service rated panel, and the main can't handle the load, then you could run into some problems. A DLC is highly recommended by me, if they paln to keep both units. One good thing you could get out of this, is finding out if both units will be used at the same time?!
Finfding out what you are dealing with is the best first step.
Another option would be to upgrade the service.

Write back when you find-out the ampacity ratings, and get more information! :)
 
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