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Thread: Split 110v off a 230v branch circuit?

  1. #1

    Default Split 110v off a 230v branch circuit?

    Is it possible to split out a 110v branch from a 230v branch circuit? I'd like to put an exterior light and 15A receptacle near my A/C compressor, but it's a 120' run back to the panel, and access it difficult.

    I've got a 230v/50A circuit supplying the A/C compressor and the compressor only requries 35A, so overloading the 50A circuit isn't an issue. The A/C circuit terminates in a fused disconnect box, and then a whip into the unit.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Not sure if this is legal, but would only be possible if they ran a neutral. If you only have two wires and ground, then no. If you have three wires plus ground, then yes. From neutral to one hot is 120vac. You'd get the same 120vac from one hot to ground, but that would not be code or safe
    Jim DeBruycker
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  3. #3

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    The 230v circuit is #6-3 w/ground. This will be inspected, so along with safety, code compliance is also important.
    Last edited by jeffeverde; 12-09-2009 at 06:33 AM.

  4. #4
    DIY Member arfeller's Avatar
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    So, if i understand correctly, you have a 6/3 + ground. So two (2) hots, one (1) neutral, and one (1) ground going to the compressor?

    If you do have the neutral then splitting out a 110 v ciruit should not be a problem. However, you might run into problems with the fused box.

    I had a fused box that would not support splitting a circuit like that so had to replace it with a subpanel. They are pretty cheap ~$35 at home depot + another ~$30 for breakers you might need.

    I recently ran 2x #6 hot, 1x #8 neutral, and 1x #10 ground to a subpanel and have a 220v circuit and two 110 v circuits.

    I'm not an electrician and am only speaking from DIY projects i have recently done.

    So make sure and get comformation of this

  5. #5
    Extreme DIY Homeowner Scuba_Dave's Avatar
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    You want to put a branch circuit on a 50a breaker ?
    DIY Handyman (not 4 hire)
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  6. #6

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    Remove your outdoor A/C disconnect and replace it with a small weatheproof subpanel. Add the proper sized 2 pole breaker for the A/C and then add a 20A single pole breaker for your outside outlet. The subpanel will act as a disconnect for the A/C so you will no longer need the disconnect.

    -rick

  7. #7
    Moderator & Master Plumber hj's Avatar
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    Default 230

    VERY few air compressors have a neutral wire, since they do not have any 110/120 volt components. In addition, the circuit breaker is primarily to protect the wires, NOT just the appliance, so any wires connected to that circuit would have to be rated for 50 amps, which is a little large for a duplex receptacle.

  8. #8
    DIY Member arfeller's Avatar
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    Ok, i think there is some confusion about the situation.

    It is my understanding that what Jeff has is:

    120' of 6/3 with ground that runs out to a fused disconnect box. From this box he has wired up the A/C unit. If this is true, there is an unused neutral wire in the circuit that could be used to make the 110v circuit.

    "The A/C circuit terminates in a fused disconnect box, and then a whip into the unit."

    If this is what he has, it is my understanding he could put an appropriate subpanel in place of this fused disconnect box (Might need to put in grounding rods and bar, i'm not sure) and then put in a appropriate 220 v breaker and 110 breaker.


    However, maybe I have this backwards and the fuse disconnect box is the source.

  9. #9

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    Quote Originally Posted by arfeller View Post
    Ok, i think there is some confusion about the situation.

    It is my understanding that what Jeff has is:

    120' of 6/3 with ground that runs out to a fused disconnect box. From this box he has wired up the A/C unit. If this is true, there is an unused neutral wire in the circuit that could be used to make the 110v circuit. . . .
    Correct

    Quote Originally Posted by drick View Post
    Remove your outdoor A/C disconnect and replace it with a small weatheproof subpanel. Add the proper sized 2 pole breaker for the A/C and then add a 20A single pole breaker for your outside outlet. The subpanel will act as a disconnect for the A/C so you will no longer need the disconnect.

    -rick
    Thanks for your input, that's what I was thinking.

  10. #10
    DIY Member arfeller's Avatar
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    Will Jeff need to add grounding rods to this sub panel in install a ground bar kit?

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    Electrical Contractor jbfan74's Avatar
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    Quote Originally Posted by arfeller View Post
    Will Jeff need to add grounding rods to this sub panel in install a ground bar kit?
    He will not need the ground rod, but he needs a ground bar kit, and lose the bonding screw.
    Yes I am A Pirate-Jimmy Buffett

  12. #12
    Moderator & Master Plumber hj's Avatar
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    Default Ac

    Right now, using common wiring pracices, the "third wire" should be the ground, NOT a neutral. IF so, and he converts it to a neutral, he WILL need a ground of some kind.

  13. #13

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    Quote Originally Posted by hj View Post
    Right now, using common wiring pracices, the "third wire" should be the ground, NOT a neutral. IF so, and he converts it to a neutral, he WILL need a ground of some kind.
    You're correct in that the whip to the device is just hot/hot/ground. But the existing wiring to the disconnect is a 3 conductor + ground NM-B --- maybe planning ahead for someone needing to split 110v off?

  14. #14
    Extreme DIY Homeowner Scuba_Dave's Avatar
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    With 6-3 you have 2 hots, neutral & a ground

    6-3 has 4 wires
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  15. #15
    Moderator & Master Plumber hj's Avatar
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    Default Wiring

    More likely an electrician who had the wire on his truck, or assumed that ALL 220/240 circuits needed a neutral, the same as electric ranges and dryers. Few would ever think ahead for that purpose, since a subpanel at an A/C unit would be a decidedly rare installation. Not all 6/3 wires have grounds, so until you specified that yours did it was not obvious. WHERE is that third wire connected now, since it should have no purpose in life, or need to exist.

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