conduit capacity

Discussion in 'Electrical and Wiring' started by farmkid, Nov 11, 2016.

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  1. Nov 11, 2016 #1

    farmkid

    farmkid

    farmkid

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    I'm adding another outbuilding to my yard and need to run some wire out to it. I would like to run a 40 amp circuit to it, which would require three #8 wires. To run this out to the building requires a ~100 foot buried conduit.

    I already have a buried 1/2" PVC conduit with #12 wires in it that goes to a chicken coop right next to the new building and I could save a lot of work by using that conduit. So, my plan would be to cut into that conduit near the new building, run it into the new building and pull the new wires through it. Conduit capacity charts say that 1/2" PVC can handle a maximum of three #8 wires. My question is how tight will that be? Will I be able to pull the new wires through that conduit? FYI, there are two elbows along the way and a total of about 90-100 feet of conduit.

    My other options are (1) digging a new trench and replacing the 1/2" conduit with something larger, which will require digging through tree roots and going under two sprinkler lines, or (2) downsizing to #10 wire and reducing the circuit to 30 amps instead of 40. I suppose I could try the #8 wire and then downsize if I can't pull it through, but I would rather find out it won't work before spending $100 on the wire.
     
  2. Nov 11, 2016 #2

    afjes_2016

    afjes_2016

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    First off if you are running a 40amp circuit I would assume it will be to a sub panel. In this case you will need 4 wires not 3. Two hots, one neutral and a ground wire. Then at the sub panel a ground rod since the building is detached. You are right at the threshold of voltage drop with the length. So you may want to consider up-sizing the conductors.
     
  3. Nov 11, 2016 #3

    Snoonyb

    Snoonyb

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    As well as running the chicken coop off of the new sub panel.
     
  4. Nov 11, 2016 #4

    kok328

    kok328

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    Some say 'overkill' I say 'forward thinking', ALWAYS run larger than what you need for future needs.
    Needless to say, tear it all out and run a minimum of 1" conduit.
     
  5. Nov 11, 2016 #5

    nealtw

    nealtw

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    If only the last guy had over killed just the size of the conduit.
     
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