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  • wiring detached garage

    Just wanted to get some advice before I started. I bought an old house with detached garaged about 60 ft away. It is currently fed by 10/2 wire going to an old 60 amp fuse panel. I want to upgrade to a 100 amp breaker panel in the garage using 8/3 wire with a 40 amp breaker in the house main panel. There's nothing out in the garage drawing a huge load, but I do want to eventually put a welder out there so I want to add a 240V circuit. Is 8/3 with the 40 amp breaker sound about right to people or should I beef it up.

    Thanks in advance.

  • #2
    Re: wiring detached garage

    Please give it some thought and then list everything you wish to run in your garage over the next several years. What is the current rating of your main breaker or the fuses in the main safety switch for your house?

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    • #3
      Re: wiring detached garage

      In my area, if you put a 100 amp panel in the garage, you need to size the wiring run to support 100 amps to that panel - even if you only are running a 40A breaker in the house load center. I once wanted to do something like you're suggesting to use a panel that I had without a major nasty amount of trenching and conduit etc....and the inspector nixed the plan, saying that the wiring needed to match the ampacity of the sub panel.

      So, unless your local code allows differently, you will need more than 8 gage. Your garage is 60 feet away but the wire might have an installed length of 80 feet. You also have to figure out continuous v. non-continuous load, ambient temp, etc. but I think you're probably looking at around #1 for a 100A subpanel - but you will need to visit the NEC to be sure. Don't rely on the "wire size calculators" you find on the internet.... they aren't all compliant with the NEC.

      I always think it's a good idea to bring both legs into a garage. Use a 100A 2-pole breaker in the house panel...then you can put single pole breakers in the "main lug" type subpanel for your 120V circuits and double pole breakers for your 240V stuff.

      Also check your code... I think you'll need a separate earth ground (rod or buried plate) for the sub panel. Make sure you do the grounding and bonding correctly. That's the #1 thing the inspector is looking for (around here anyway) and is critical for safety.

      Good luck~

      -Andy

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      • #4
        Re: wiring detached garage

        Andy I would have fought the inspector up and down on that one, that is the dumbest thing I have ever heard an inspector do and obviously the inspector is not an electrician and knows nothing of codes. There is no reason whatsoever to require the correct size wire for the panel like that. The main breaker in a subpanel is doing nothing essentially short of being a disconnect. The breaker in the main panel is what will determine how much amperage will flow on those conductors. The over current protection ALWAYS goes ahead of what you are protecting, the main breaker does nothing more than protect the panel equipment. You don't even need a main breaker at the subpanel.

        The #8 will be fine to feed a 40 amp sub panel. You will need a seperate ground rod driven at the garage as well. A 60 foot run plus enough to get into the panels isn't enough to worry about voltage drop.

        Jeff
        Last edited by piette; 02-13-2009, 12:34 PM.

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        • #5
          Re: wiring detached garage

          The way you want to do it is fine. I never use uf cable, so I would run conduit and use thwn wires to feed the garage.
          As Jeff stated, don't forget the ground rod at the garage!

          Comment


          • #6
            Re: wiring detached garage

            I agree with jeff and jbfan has a good point about running condit. just a note that i am a retired elect. of 38 years. nuff said

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            • #7
              Re: wiring detached garage

              I recently did the same thing you did but my garage is slightly farther then yours. I used #2 RHW-2 aluminum wire in pvc conduit out to the garage. The price for the aluminum wire is probably the same or less then #6-#8 copper and is good to an 80amp breaker with up to a 40amp continuous load. The only thing you have to make sure you do when using aluminum wire is use anti-oxidant compound and torque the lugs to the rating on the breaker.

              I know some will say not to use aluminum which is fine and their choice but when installed correctly and it is easy to install correctly there are no issues.

              I currently have the garage on a 60amp breaker.
              Last edited by Palomino; 02-13-2009, 02:31 PM.

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              • #8
                Re: wiring detached garage

                Hi Jeff,

                Thanks for your comments. I replaced an old dilapidated panel with a new 125A subpanel. The new subpanel is "main lug" without a main breaker. The existing wiring was #6. My original plan was to feed the subpanel with a 60A breaker in the house load center, which I figured would protect the #6 wire and make everything OK. The inspector's problem was, he said, that in the future someone might swap out the 60A breaker in the main house load center to get more current to the subpanel, seeing as the subpanel was rated for 125A. If they did this, the wiring between the house load center and the sub wouldn't be adequate. So his point was that I needed to have wiring that supported the "nameplate" limit of the subpanel. At the time I thought the argument was a little over the top but what can I say... he is supposed to know the code, or so I thought. It did cost an arm and a leg to put that big wiring in and a 125A breaker in the main panel!

                Turns out I ended up putting a big TIG welder in the garage and use most of the 125A anyway, so it all worked out in the end.

                Thanks,

                Andy

                Comment


                • #9
                  Re: wiring detached garage

                  Originally posted by Andy_M View Post
                  Hi Jeff,

                  Thanks for your comments. I replaced an old dilapidated panel with a new 125A subpanel. The new subpanel is "main lug" without a main breaker. The existing wiring was #6. My original plan was to feed the subpanel with a 60A breaker in the house load center, which I figured would protect the #6 wire and make everything OK. The inspector's problem was, he said, that in the future someone might swap out the 60A breaker in the main house load center to get more current to the subpanel, seeing as the subpanel was rated for 125A. If they did this, the wiring between the house load center and the sub wouldn't be adequate. So his point was that I needed to have wiring that supported the "nameplate" limit of the subpanel. At the time I thought the argument was a little over the top but what can I say... he is supposed to know the code, or so I thought. It did cost an arm and a leg to put that big wiring in and a 125A breaker in the main panel!

                  Turns out I ended up putting a big TIG welder in the garage and use most of the 125A anyway, so it all worked out in the end.

                  Thanks,

                  Andy
                  Gladto hear it worked out for you in the end, but the inspector was still very much wrong on that. An over current protection device (a breaker) is only intended to protect the equipment downstream of it. An inspector can not make you rate all the equipment to the highest rated equipment, rather he has to make you rate for the lowest rated equipment, which typically is the conductors.

                  Just remember if an inspector tells you something you don't like, he can not enforce anything he can't show you in writing. If he says it is a local code, he HAS to show you that local code. Just telling you it exists does not cut it.

                  Jeff

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                  • #10
                    Re: wiring detached garage

                    Thanks for your responses everyone. Woussko...in the house I've got a 200 amp main breaker panel.

                    Jbfan...is running the individual wires with conduit cheaper, easier, or both?

                    Comment


                    • #11
                      Re: wiring detached garage

                      Originally posted by tazimina View Post
                      Thanks for your responses everyone. Woussko...in the house I've got a 200 amp main breaker panel.

                      Jbfan...is running the individual wires with conduit cheaper, easier, or both?
                      It is neither cheaper nor easier, but it is the better way. Running the conductors in conduit offers much better physical protection for the conductors. Also if you run a larger pipe than required, you have capacity to pull them out in the future and run larger feeders to that garage in the future.

                      In either case you are digging a trench, shallower if you run your conductors in conduit. You are buying the same amount of wire ineither case as well, so really it is just a matter of the conduit and fittings being the extra expense. That extra expense is well worth it in my opinion.

                      Jeff

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                      • #12
                        Re: wiring detached garage

                        Originally posted by tazimina View Post
                        Thanks for your responses everyone. Woussko...in the house I've got a 200 amp main breaker panel.

                        Jbfan...is running the individual wires with conduit cheaper, easier, or both?
                        Neither. Cable will be the easiest, just dig the hole, drop in the cable, and cover.
                        I haven't priced cable in a while, so I'm not sure of the cost difference.
                        I just like pipe and thwn wire. It is much easier to replace if down the road you have problems, such as lighting.

                        Comment


                        • #13
                          Re: wiring detached garage

                          I like the response of the guy who said "stop and think about what you want to put in your garage, then proceed" I would only run a feed once, and I would run it as big and protected as I could afford in the budget. The first thing you need to look at is the home panel. Unfortunately most builders and electricians will only put a panel in a home that is just big enough for the home, nothing for the future. If you add a load such as 50 amps to your home and it is not capable, you can potentially burn up your home panel. Second, for loads 60 amps and larger I would run aluminum URD wire and in pipe, unless you want to run it 36" deep or run it agian after a tree or gopher/mole gets it (the tunneling varmits are drawn to the heat) The issue with aluminum is you can't travel more than 3ft into your home with it and possibly cannot have it at all with some local codes. Other than those factors, as long as you run a ground and protect your wire with the proper size breaker, you should be OK. Don't feel bad about maybe getting a few free estimates from local companies, listen to what they recommend, and maybe they will hit you with a price or reason that makes it worth your while.

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