# For the electricians. Running power to a detached garage.



## jpollman (Jan 14, 2001)

Hi folks,
I know that we have some licensed electricians here so I thought I'd pick your brains a bit. My father lives in Troy and we built a detached garage at his place a few ago. Probably four or five years ago, we rented a trencher and installed some conduit and #10 wire so we could get power out to the garage. We got the conduit in, wire run, and buried the conduit. We never took it any further than that. It got late in the season and we figured we'd finish up in the spring. Well things got busy and we just never got back to it. Since then he's been using heavy gauge shore-power cord he used to use for his boat to get power out there. 

He just wants a few lights and outlets as well as a 220 circuit for his compressor. Installing the lights and outlets is no big deal once I get the power out there. I believe that he has an unused two pole 30A circuit in the basement that we can use to power the garage. As I said, the #10 wire is already out there and coiled up but not being used. We just need to get a sub-panel installed to connect the branch circuits to for lighting and outlets. 

I was at HD today and saw a sub panel box with six spaces that should be fine. It's good for up to 100A. Could that box just be installed or does it need to be a box with a main also? Again, this is just going to be a 30A circuit. I just don't know if that sub-panel needs a main or maybe just run the wires to a 30A disconnect and then the sub-panel from there. 

I just don't know what the code would be for this situation. I'm sure that I can wire it once I know how it needs to be done, but I just want to get it right the FIRST time.  He's in Florida until May, but I don't have much going on right now and it would be nice if I could get it done while he's gone and have it finished when he gets back. It's another one of those unfinished projects that I'd like to complete for him.

Thanks for any input!

John


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## redshirt32 (Aug 20, 2003)

John, 
I'm not an electrician. But in Warren I had to bury it 42" and the 100A box installed had to have a twin copper ground installed plus a main for the 220A. So that ate up 2 circuits I was planning on. I already had the box installed under advice from an electrician. Maybe he didn't like me or somthing.Had to have it reinspected.


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## jpollman (Jan 14, 2001)

Oh yeah, I left out the ground rods. I was planning on that but forgot to mention it. Thanks for the input.

I don't have a current code book to look this stuff up. Hopefully one of our electricians here will know for sure what's needed. We just want to make sure it's up to code.

John


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## The_Don (Apr 28, 2008)

For what its worth Mine has a disconnect before the panel in the garage and no main. I need to redo the panel in my garage its a mess. When i do i intend to put in a panel with a main regardless if its needed or not, it will be much easier than running out to the disconnect when you need to stick your fingers in there.


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## jpollman (Jan 14, 2001)

Well I could probably figure this stuff out if I could get hold of a code book. But there's so much to it that I may miss something. I was hoping that maybe one of our electricians could see what I'm trying to do and see if it's kosher or not. It seems pretty simple to bring a 30A 220V circuit from the house to the garage. I just need to figure out how to terminate it in the garage. Once I know the correct setup, I can buy it and install it. When that's done, running two or three branch circuits is a piece of cake.

John


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## BIG DAVE (Mar 3, 2003)

hey john!!! the sub panel does not need to be a main breaker...
the wire is protected by the breaker in the house, also you should
have 4 wires from the house too the garage!!! 2 hots, ground
and neutral.... you have to isolate the grounds and neutrals in the
sub panel. how big the compressor you have??? mabe get rid of the 
#10s and run #8s or #6s... never know what you might need in the future!!! i can come out and give you a hand if needed...
also can come
by and fix your kitchen problem the same day... dave


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## jpollman (Jan 14, 2001)

Thanks Dave!

I'm going to head down to my dad's later this week and see just exactly what we pulled in the way of wire. As I said, it's been about four or five years since we did it and my memory isn't what it used to be.  

We probably pulled four tens (two hot, neutral, and ground). It's not a big compressor. It's just a small portable probably 20 gal. Craftsman. He just likes running it on 220 because it's less current draw that way.


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## Rumajz (Dec 29, 2005)

I second that bigger wire idea unless you are absolutely sure you (he) won't need more devices in the future. An 8 gauge would be nice.


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## eprice (Dec 28, 2010)

I can quote you the code and all the exceptions you can or cannot take; but the easiest way is to go to home depot and buy a load center with a main breaker, install the ground rod. This will satisfy any local inspectors.

You should also increase the wire size.


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## boppa (Jul 18, 2003)

You can't feed a 100A sub panel with 30A wire- even if you are sure you or your Dad won't use more than 30A. The next guy who buys the house won't know you only fed the 100A panel with #10 wire. He'll pull more circuits out of that 100A panel and start tripping the overcurrent device feeding the garage panel. Circuit breakers are WAY less reliable than fuses and they may not open on overloads like the one that could occur. You do not want a stuck CB to cause a fire in the house panel.


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## jpollman (Jan 14, 2001)

I'm going to head over there later today or tomorrow and see what wire is there already. I'm reasonably sure that it's at least #10. The garage is about 60-70' from the house so I don't know if it's going to be possible to pull that wire back out of there. If it was, I'd probably replace it with #8 but that's a slim possibility. I talked to my dad last night and he said that if it turned out that whatever is in there isn't big enough, we'd just bite the bullet and trench it again and install the right size wire. He just wants to be sure it's done correctly to code. I really think that a 30A circuit is going to be fine though. He just needs two or three 8' fluorescent lighting fixtures, a few outlets, and his compressor. He's only going to run the occasional power tool out there really. The compressor isn't a huge one either. It's a small probably 20 gallon with a 1hp motor on it. A 20A 220V circuit for that will be fine.

John


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## WALLEYE MIKE (Jan 7, 2001)

John, I did mine as you are thinking. I ran #6 to a sub panel. I do have a larger compressor tho. 220v on a 20A circuit by itself. And a 50A for the welders. Wanted to make sure I had enough juice so I went with #6.


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## boppa (Jul 18, 2003)

First of all, you probably should contact your local electrical inspector and get his take on your situation. That being said, #10 wire is good for 30A- that's it. I'm assuming you have installed 65 or 75 degree C wire. Therefore in the garage you cannot have a subpanel larger than 30A or a switch larger than 30A. Square D has 30A panels (2-15A, 120V circuits)- HD carries these. This would give you 2 lighting/ appliance circuits, but no 240V circuits. Or you could install a 30A, 240V switch in the garage to feed the compressor, but no 120V circuitry. With the wire you have, you can't do both, at least not legally.


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## jakeo (Sep 14, 2004)

boppa said:


> First of all, you probably should contact your local electrical inspector and get his take on your situation. That being said, #10 wire is good for 30A- that's it. I'm assuming you have installed 65 or 75 degree C wire. Therefore in the garage you cannot have a subpanel larger than 30A or a switch larger than 30A. Square D has 30A panels (2-15A, 120V circuits)- HD carries these. This would give you 2 lighting/ appliance circuits, but no 240V circuits. Or you could install a 30A, 240V switch in the garage to feed the compressor, but no 120V circuitry. With the wire you have, you can't do both, at least not legally.


This can be done LEGALLY very easily. First off, just because the wire is rated for 30 amps, you have to take in consideration the voltage drop from the house to garage. So you install a little 6 circuit sub panel and run the 2 blacks to the main lugs, the white to neutral bar and bare to ground bar..SEPERATED FROM THE NEUTRALS.. Next you run your circuits and put up to 6 breakers in there and check with inspector if they require a ground rod.....theres a big contraversy about that going on now.
You can put the compresser on a 20a 2pole and the others on 15amps single pole. 
The quote above makes NO SENSE WHATSOEVER because you are using the #10's comming in as the feeders and branching off from there. Its not like he has 50 tools that will be running at the same time and the compresser will only be running on maybe 12 amps....18 on start-up.
The way you are thinking will be just fine.


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