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Thread: Wiring a Sub Panel at a Shed 80' from power pole

  1. #1
    Join Date
    Apr 2018
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    FL
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    Default Wiring a Sub Panel at a Shed 80' from power pole

    Good afternoon all. I'm a mechanic, not a home electrician. My electrician is the opposite. So, We buried conduit with 3 conductor 2 Ga Aluminum wire over the weekend from the pole to subpanel location. My question is, should we have ran a ground wire with the 3 conductors or is a ground rod at the sub-panel sufficient? He says meh personal preference... That's not a good enough response for me. We're running 100A service (will never need that much 50A at best) the 80feet. I understand the 2 110 hots and 1 neutral (Which is connected to the ground bus in the main power pole box.) Is this correct? 2 ea 110 legs, one neutral, then we drive a 12' ground rod at the sub-panel location? I've read that running a ground from the power pole to the subpanel is dangerous/bad juju. Just looking for advice on this config and safety of my family, and myself. Thx ya'll.

  2. #2
    Join Date
    Feb 2012
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    Kent, WA
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    What is the source of the power for this shed -- a breaker in a panel out at the pole, or is it just tapping directly off the service wires at the meter output? 10+ years ago, you had options. Now you typically need 4 wires to a subpanel unless you are tapping the service before any circuit breaker.

    Once you hit a circuit breaker, you need 4 wires (hot, hot, neutral, ground). I recommend using a breaker at the pole (60 to 100 amp double pole) so then you must run a #8 copper ground wire in that trench before you cover it up (or #6 aluminum). The ground wire is typically smaller than the hot once you get over 30A feeders. The ground wire needs to run with those other 3 wires (through the same holes, conduits, and next to each other in the trench).

    The ground rod you must do regardless. You most likely need two 8' (or longer) ground rods that are spaced at least 6' apart. I would put #6 copper between those and to the panel ground bar in the shed. You could also use #8, but then you need to protect that #8 wire with PVC conduit so its probably cheaper just to use the #6 for the ground electrode conductor.
    Mark
    Kent, WA

  3. #3
    Join Date
    May 2018
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    Quote Originally Posted by suemarkp View Post
    What is the source of the power for this shed -- a breaker in a panel out at the pole, or is it just tapping directly off the service wires at the meter output? 10+ years ago, you had options. Now you typically need 4 wires to a subpanel unless you are tapping the service before any circuit breaker.

    Once you hit a circuit breaker, you need 4 wires (hot, hot, neutral, ground). I recommend using a breaker at the pole (60 to 100 amp double pole) so then you must run a #8 copper ground wire in that trench before you cover it up (or #6 aluminum).
    Hi Mark,
    I am new to the forum. I been searching around for the info but need clarification. I am connecting a subpanel 55 ft away from the main breaker box. The person who would do the job only wanted to use 3 wires... I am assuming 2 are hot and the other one maybe ground? Is it necessary to use 3 or 4 wire cable? At what type of breaker should I use to make the connection? He also wanted to use #6 cable. It's for a small garage maybe 2-3 ceiling lights and 4-5 power outlets.

    The underground line already exist... he wanted to charge me $300 just to pull the cable and connect the subpanel not including cable and other parts. I think I am capable of doing this with a little guidance.

    Thanks again in advance. I really appreciate any help.

    Raul

  4. #4
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    Feb 2012
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    Kent, WA
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    For a 120V only circuit, you need 3 wires: hot, neutral, and ground. For a 120/240V circuit (this is what is fed to your house panel), you need hot1, hot2, neutral, and ground. Only from the power utility are you allowed 3 wires for this (the neutral and ground are dual function in 1 wire on the service from the utility). The NEC used to allow 3 wires to a subpanel, but not anymore.

    If a single 20A circuit will power your garage, then don't put a panel there just one circuit. Even the 55' distance isn't all that far, so I'd only upsize the wire for that (10-2 w/ground UF cable fed from a single pole 20A breaker in your main panel). If one 20A circuit is not enough, then you have 2 more choices:

    A multiwire 20A branch circuit (10-3 UF cable with ground) -or-
    A feeder from 30A or more (this needs 4 wires too, but size is based on the size of the breaker feeding it)

    Finally, there is a 3rd choice for when you only have 3 wires: If the 3 wires are existing from back when 3 wires could feed a detached building, then you can use them to feed a subpanel like you would a house service (old existing feeders are grandfathered in the code). Or, you can wire the subpanel so it is 120V only (this could mislead some people thinking you have 240V available but it will be 120V only).

    If you put a panel in this detached building, then you must also install a ground electrode system (2 ground rods on a #6 wire going to that subpanel). Also note that a detached building requires a building disconnect. This can be a simple switch, a larger disconnect like used for an air conditioning unit, or a main breaker (or less than 6 breaker handles) in a panel.

    If you're not really sure what you want, I would install PVC conduit (at least 1" diameter) out to that shed and pull the wires you can afford now. If the wires exist now, then that will dictate the solution. What are the size and colors of the wires installed, are they aluminum or copper, and when were they installed (if you don't know the install date, when was the main house built and when was the shed built)?

    This is a relatively easy DIY project, but you will need to ask a lot more questions to do it right. At this point, you probably don't know what you don't know. I'd look for a book or at least read some of the articles here: Wiring Done Right Electrical Switch Outlet Safety and maybe google for "subpanel wiring to an outbuilding".
    Last edited by suemarkp; 05-11-2018 at 10:47 PM.
    Mark
    Kent, WA

  5. #5
    Join Date
    May 2018
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    Sorry for the delay response. I been extremely busy. I really appreciate all the help and detail. I was going to do it this week, but I'll wait a little. That wire is expensive lol.

    Thats a lot again. I google and youtube this... I am confident I can do it.
    Thank You again

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