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Discussion Forum

Running power to small shed

cilwww | Posted in General Discussion on August 16, 2006 10:06am

I’m wanting to run power to a small 10×10 shed in my back yard. We intend to turn it into a small workshop for our kids who have an interest. Tools that might be in the shop eventually include a miter saw, jig saw, perhaps a small table saw, sander, band saw, small dust collection system and miscellaneous hand tools. I have about 75 ft run to the shed from the service in the house. I intend to bury the cable. I also would like to put a small electric heater in the shed to make it somewhat reasonable to work in during the winter. My guess is that I can get away with 2 circuits. I understand that I should put in a subpanel in the shed as well.

I’ve done some of the wiring in my home with help from some more experienced friends, but it has been a while.

I am not sure how to ask my questions, but here goes…

1. Can I get away with running a 30 amp circuit to the shed – using 10/2 and then put 2 20-amp circuits there?

2. Or should I be running a larger circuit – say 40 amp? If so – do I run 8 guage wire? My guess is that 60 amps is overkill.

Any advice on this would be appreciated.

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  1. junkhound | Aug 16, 2006 11:39pm | #1

    As small as 10x10 with no 240 V tools, and if you are going to simply hand dig a trench, I'd just put in a 12-2 w/g UF for a single 20 A circuit, which is enough for small tools, lights, and for a floor space heater.

    However, if you are going to rent a trencher or something, you might as well put in conduit and a 50A circuit to run a welder and all the heat it will ever need.  Let your finances dictate.

    Throw a few other signal wires into the trench also; phone, cable, doorbell wire triplex, etc.  I even throw in a 1/4 inch air hose to the trenches to my sheds to keep and air tank charged if needed. By the time I dig the trenches, I always figure to put a 50 A circuit in there while I'm at it.  May change my mind on the next trench the way copper prices have quadrupled.

    1. User avater
      BillHartmann | Aug 17, 2006 02:28am | #5

      At a very small increment in cost he can run 12/3 and with a multi-wire circuit and have 2 20 amps 120 volt circuits.Still treated as a single circuit so no panel, disconnect, or ground rods needed.

  2. BUIC | Aug 17, 2006 12:00am | #2

    For two 20 amp circuits you'll need two 10-2 home runs or one piece of 10-3.

      And if I were digging a 75' trench some conduit (empty) would be going in there. For $30 worth of material, any unforseen needs would be taken care of...Buic 

  3. renosteinke | Aug 17, 2006 01:35am | #3

    The old "power to the shed" project. It's a great idea; however, the NEC is not a design manual, nor is it an instruction manual for the DIY. I'd like to share here some suggestions, that have proven to be, well, practical.

    First of all, power to the shed usually means that the shed now needs a building permit. Don't doubt for a minute that some neighbor won't fink on you...

    How much power? Well, that's where the troubles begin. What is fine today never seems to be fine for very long. So, I suggest that you plan for growth.
    So, when you run your wires...don't just dig, but dig DEEP. At least 18", 24 is better. You absolutely want the wires below the length of a shovel blade; this protects you from the errant gardener.
    Plastic pipe is pretty cheap. I'd run at least 1" pipe; this leaves plenty of room for larger wires when you need them.

    While you've got the ditch... why not also run pipes for water and maybe even phone / cable / alarm wiring? You need not use them right now- just cap off the ends. As you might guess, I HATE digging, and want to have to dig only once.

    Small panels, even outdoor ones, are pretty cheap. I usually mount a disconnect on the outside- that's what my pipe runs to- and then punch through the wall just once to a large junction box. You'll also want to have a ground rod, in addition to the ground wire from the house panel.

    How big of a panel? I'd suggest room for at least six full-size breakers. You'll appreciate the extra working room inside the box.

  4. junkhound | Aug 17, 2006 02:09am | #4

    AH, now you see where this is leading. 

    Once you have power, phone, cable, water, air, etc. to the shed, it is time to add on to it.  Pretty soon you will have a guest cottage, so better figure on a 60 A subpanel at least <G>, and dont forget a gas line for the heat for the cottage, unless a HP is better in your locale.

    NO joke, son built a 9 by 12 shed, filled that, now his need has expanded an 800 sq ft outdoor office with HP and AC, figure a couple of 3/0 copper to that one should do it.

  5. Fisher1009 | Aug 17, 2006 05:51am | #6

    i did my detached garage last year for almost exactly the same purpose.

    i would definitely recommend a sub-panel if budget/time permit- if your kids get serious about this, 2 20A circuits will not be enough, especially if two are working at a time.  also, its a good idea to have dedicated circuits for each of the tools.  otherwise if you are running a saw, dust collection and lights all at once, you are going to be at max capacity.  throw in that heater and somebody's gonna be makin a lot of trips back inside to reset teh breaker.

    i found that lowes/home depot both carried standard 60A kits that included a couple of breakers and a box with space for 10 circuits (20 if you use the "slimline" breakers").  i found the cheapest way to wire the run was to buy a 500ft. spool of 8 gauge THHN wire (THHN wire is one individual strand, as opposed to romex which is either 3 or 4 strands, depending on teh application).  

    typically, 8 AWG romex is not adequate for a 60 A line. however thhn going thru a conduit has different insualting properties from romex, and 8 AWG THHN wire will therefore be adequate for this application. 

    i believe 18" is the minimum depth for setting the conduit underground.  i rented a ditchwith for about $100, and it took me about an hour to dig the trench.  with all the wireless technologies available today, i personally wouldnt' worry about running any other kind of wiring through the conduit.

    of course if you you're not certain about this stuff, then get an electrician.

  6. cap | Aug 17, 2006 06:13am | #7

    Check out the Nov 2004 issue of Fine Homebuilding, there's an article on exactly what you plan to do.

    If you don't have the issue, you can buy it from the FH on-line archive.

    Anyway, if I were you, I'd run some 1" Sched 80 conduit, 24" below grade (as required by Code), and run a 20 amp multiwire circuit--that'll give you two, 20 amp circuits.  Use THHW wire in the conduit.  You have to have a disconnect at a separate structure, so the shed end of the pipe gets a two-gang box and two snap switches (motor-rated switches, that can handle higher amperage than a garden-variety 39 cent switch).  Those are your disconnects.  Some lights and some receptacles on one circuit, other lights and receptacles on the other.

    If the kids run so much equipment that the breakers trip, then install a small (60 amp, 6 or 8 pole) subpanel, ground rods, and more circuits.  The 1" conduit will make it easy to upgrade. 

    Have fun,

    Cliff

    1. User avater
      SamT | Aug 17, 2006 06:01pm | #8

      I feel so inadequate.

      I cut the male end off an old extension cord, wired it to a GFCI outlet and put a light ciruit downstream. Bored a hole in the wall and put a weather proof switch cover on it.

      Stick an extension cord thru the hole and plug in the GFCI.

      No permits required.SamT

      1. User avater
        McDesign | Aug 18, 2006 02:25am | #10

        My first shop (I was in 8th grade); I wired by plugging in an heavy-duty extension cord to an outdoor non-GFI outlet; ran the cord 25' to 5 duplex outlets and 2 overhead fluorescents.  It was a pre-fab 10x16' metal skinned bldg.

        Lots of happy work there!

        The upshot is, that was in 1976.  My folks still live in the same house, the shop's never been rewired, dad still uses it, still works fine - I sharpened drill bits there Wednesday with dad's Drill Dr.

        Not hat I would recommend that, but - it was a simpler, more natural time.

        Forrest

         

    2. r | Aug 18, 2006 02:04am | #9

      Has the code changed regarding the minimum coverage requirements ?  My 1999 NEC in Table 300-5, Column 3, says that if he does use Schedule 80 PVC he can run any size conductors buried 18"

      1. TJK | Aug 18, 2006 02:38am | #11

        I believe the requirements changed at the end of '02. Buried drops have to be at least 24" below grade out here (CO). The guy who was building a garage for me found that out the hard way. His 100-ft x 18" trench had to be deepened another six inches, and he spent the better part of a morning doing it by hand :-(

        1. User avater
          BillHartmann | Aug 18, 2006 02:52am | #12

          The proposed 2008 draft NEC shows 24" for direct burrial cable and 18" for nometalic raceway.

        2. r | Aug 18, 2006 03:22am | #13

          I just looked at the 2005 NEC online, and the requirement for buried conduit is still 18".  Your contractor may have been using UF (direct burial cable - no PVC conduit), which would require 24" of cover.  Or it could be local code, or a mis-informed inspector.

      2. cap | Aug 18, 2006 06:42pm | #14

        Yup,  you're correct.

        It's 24" for direct-bury cable or conductors.

        Thanks for catching my mistake.

        Cliff

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