Split 110v off a 230v branch circuit?

Discussion in 'Electrical Forum discussion & Blog' started by jeffeverde, Dec 9, 2009.

  1. jeffeverde

    jeffeverde New Member

    Messages:
    79
    Location:
    L.A.
    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. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,814
    Location:
    New England
    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
  3. jeffeverde

    jeffeverde New Member

    Messages:
    79
    Location:
    L.A.
    The 230v circuit is #6-3 w/ground. This will be inspected, so along with safety, code compliance is also important.
    Last edited: Dec 9, 2009
  4. arfeller

    arfeller New Member

    Messages:
    77
    Location:
    Port Angeles, WA
    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. Scuba_Dave

    Scuba_Dave Extreme DIY Homeowner

    Messages:
    885
    Location:
    South of Boston, MA
    You want to put a branch circuit on a 50a breaker ?
  6. drick

    drick In the Trades

    Messages:
    392
    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. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,263
    Location:
    Cave Creek, Arizona
    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. arfeller

    arfeller New Member

    Messages:
    77
    Location:
    Port Angeles, WA
    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. jeffeverde

    jeffeverde New Member

    Messages:
    79
    Location:
    L.A.
    Correct

    Thanks for your input, that's what I was thinking.
  10. arfeller

    arfeller New Member

    Messages:
    77
    Location:
    Port Angeles, WA
    Will Jeff need to add grounding rods to this sub panel in install a ground bar kit?
  11. jbfan74

    jbfan74 Electrical Contractor

    Messages:
    131
    Location:
    Newnan, GA
    He will not need the ground rod, but he needs a ground bar kit, and lose the bonding screw.
  12. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,263
    Location:
    Cave Creek, Arizona
    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. jeffeverde

    jeffeverde New Member

    Messages:
    79
    Location:
    L.A.
    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. Scuba_Dave

    Scuba_Dave Extreme DIY Homeowner

    Messages:
    885
    Location:
    South of Boston, MA
    With 6-3 you have 2 hots, neutral & a ground :confused:

    6-3 has 4 wires
  15. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,263
    Location:
    Cave Creek, Arizona
    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.
  16. jeffeverde

    jeffeverde New Member

    Messages:
    79
    Location:
    L.A.

    Sorry, I forgot to add :p after "planning ahead" :)

    The NM-B terminates in a junction box, then jumpers for the hot pair run through a mud ring and bushing into the back of the disconnect box mounted outside. The neutral was capped off with a wire nut in the junction box.
    Last edited: Dec 12, 2009
  17. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,263
    Location:
    Cave Creek, Arizona
    wire

    In that case your original plan for a sub panel is viable.
  18. jar546

    jar546 In the Trades

    Messages:
    432
    Location:
    USA
    Ahh,...yes, yes it is an issue.

    What is the motor FLA, FLC, HP & Service Factor
  19. codeone

    codeone Code Enforcement

    Messages:
    160
    Location:
    North Carolina
    What is the minimum circuit ampacity for you a/c?
    What is the max breaker size for your a/c?

    These facts are needed to do the calculation you need.
  20. codeone

    codeone Code Enforcement

    Messages:
    160
    Location:
    North Carolina
    The issue is if your minimum circuit ampacity is 35A you haved to multiply 35 x 125% to come up with your calculated load for the circuit. This is for start up current.

    35 x 125% = 43.75 or 44A
    50A - 44A = 6A
    Dont have as much extra as you thought!

    Now if the 35A is you max breaker size you might be ok.
    Give us some more info please.
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