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Thread: Electrical question. Running power to a detached garage.

  1. #1
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    Electrical question. Running power to a detached garage.

    Hi gang!

    I've seen a couple electrical questions here lately and saw some pretty detailed answers which leads me to believe that we have some electricians on board. Well I've got a question.

    I'm not an electrician but do understand the basics and can change out fixtures, switches/outlets, etc. I've wired an addition on my house so I can do a lot of this stuff but I don't work with it every day so it takes me a while to figure it out by myself if I've got to wade through all of the codes and such. Maybe someone here will know what's required and save me a lot of research. Here's what's up.

    Probably ten years ago we built a detached garage at my fathers house. It sits back probably fifty feet from his house. We decided to add power later on after it was finished. Probably five years ago, we dug a trench and installed some conduit and wire in preparation for wiring the garage. We finished that phase of the project but it was late in the season and we decided to finish in the spring when he got back from Florida. Well as usual, things came up and we never got back to it. For the past five years, he's been using a long heavy duty shore-power cord he used to use for his boat. That's getting to be a pain and besides that, I hit it with the snow blower the other day when over there clearing the drive! Luckily I just nicked the outer insulation and there was no damage. After that close call, I decided that it's time to get this project FINISHED. He's in Florida until May but I'd like to get it done for him before he gets back.

    We pulled a set of #10 and a set of #12 wire in the conduit. One for the supply and he wanted another set thinking that he might want to add a switch so he could control some flood lights out there from the house. I think he has an unused 30A double pole breaker in the service panel in the house. I was thinking we could just use that to feed a 30A 220V circuit to the garage. I only need three or four circuits in the garage. I'd probably put the lighting on one, outlets on another, and a 220 circuit for his compressor.

    Hooking the wire into the service panel in the house is no problem, but I need to know what kind of a box I need in the garage. I can buy a 60A six place sub panel and install that. But I'm thinking that I need a main breaker. The problem is that the smallest main service panel I'm going to be able to get is a 100A. I don't think that I could connect that large of a panel with #10 wire. I can get a 30A disconnect and run the wire to that and mount it next to the 60A sub panel and feed the sub panel from the disconnect. Would that be feasible?

    Again, I'm sure I'm capable of doing this wiring but I just need to know what the setup should be. It will take me a while to figure it out and I may miss something if I just start going through the code book. Oh yeah, a couple ground rods is no big deal either. I'll put those in too.

    Thanks for any input you may have!

    Take care and have a great day.

    John
    "The bitterness of poor quality remains long after the sweetness of low price is forgotten"

  2. #2
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    The main breaker will be the one in the house. So the 60 amp sub panel would be the ticket.
    The problem is the wire size. A 60 amp sub panel should be run off a 60 amp breaker. I'm guessing for the run from main panel to sub the wire should be at least 6 gauge might even have to be bigger.
    The 10 you have pulled in is big enough for a 30 amp 220 outlet that's it. And the 12 would be good for an outlet or two and the lights. As for 220 on that 12 maybe 20 amps
    It could be worse You could be on fire.
    Stupid hurts.

  3. #3
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    OK thanks. I'll be going back over there in the next few days probably. I go over and check things out about once a week to be sure things are OK while he's in FL.

    I'll see what we pulled for wire in the conduit. For some reason, a set of #10 and a set of #12 comes to mind but I'm not positive. I'm sure a 20A 220V would be fine for his compressor, it's not a big one. Maybe if there is just a set of #10 and #10 I could split it up that way and run the 220 off of the 10 and the 110 off of the 12. The other loads out there aren't going to be much, just some fluorescent lights and outlets for a power tool or two. Nothing big.

    I'll let you know what I find out.

    Thanks!

    John
    "The bitterness of poor quality remains long after the sweetness of low price is forgotten"

  4. #4
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    What are you calling a set?
    Did you pull in 3 or 4 strands of 10 and a ground?
    It could be worse You could be on fire.
    Stupid hurts.

  5. #5
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    I'm pretty sure we pulled at least three tens (2 hots and a neutral). There's probably a ground in there too.

    John
    "The bitterness of poor quality remains long after the sweetness of low price is forgotten"

  6. #6
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    It could be worse You could be on fire.
    Stupid hurts.

  7. #7
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    Sacramento, CA
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    You don't NEED a main disconnect at the subpanel end. Your house's main breaker serves that need.

    Also, you absolutely can feed a 60a subpanel with a 30a circuit. The amperage on the panel is just the max load you can pull with it. You don't have to feed it that much. If you pulled too much, the breaker on the house will trip and protect your wiring, too.

    Since it IS a detached garage, you may be required to drive a ground rod just for it and NOT run a ground from the house to the garage. That's how it works here, and I believe most other places. Check your codes - I think you need your neutral to be separated from ground at the subpanel.

    I would do the 60a panel which leaves you plenty of expansion room down the road. I used a 125a subpanel and fed it with 60a for a few years. I'm about to pull #2 wire and give it 100a soon. With wiring, always plan for the future.
    Jason Beam
    Sacramento, CA

  8. #8
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    Cool!

    Thanks guys. That's kind of what I was thinking. The sub panel I was looking at was rated at 60A max. That doesn't mean that it will be supplying that much. Because this circuit is being fed off of the main panel in the house, I figured the main would serve that purpose. But it might make it easier to just put a 30A disconnect in the garage to make it easier to shut the power off to the sub panel. Installing a couple ground rods isn't a big deal either.

    Like I said, I'm going over there later this week and I'll see just exactly what we pulled in the way of wire. It was about five years ago and my memory isn't what it used to be.

    Thanks again!

    John
    "The bitterness of poor quality remains long after the sweetness of low price is forgotten"

  9. #9
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    I would use the existing #12's to pull new # 6 wire, Pull enough for 2 hot, a neutral and a ground. You may not need more then 30 Amps now but it's nice to have the capacity for later.
    "There’s a lot of work being done today that doesn’t have any soul in it. The technique may be the utmost perfection, yet it is lifeless. It doesn’t have a soul. I hope my furniture has a soul to it." - Sam Maloof
    The Pessimist complains about the wind; The Optimist expects it to change;The Realist adjusts the sails.~ William Arthur Ward

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