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Home Wiring: 230 VAC 1ph motor Question?

Discussion in 'Electronic Basics' started by N., Dec 1, 2003.

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  1. N.

    N. Guest

    The building I live has in the past only been wired for 120VAC
    service...it is a WWII era building and had weak electric service. A
    couple years ago the owner did an electrical upgrade and installed a
    breaker panel (previosuly there was just a fuse box with screw in
    fuses) in my apartment and promised 220VAC service. Before the work
    was completed, the owner ran afoul with an asbestos issue in the
    basement and the second phase of the electrical service was never
    connected by the electrical utility. So, we've only had 120VAC
    service.
    I want to hard wire a compressor that has a 230VAC single phase motor,
    drawing 22 FLA. Recently, I checked my service box and finally I now
    have 220VAC service.
    My question regards the circuit's grounding and connection to the
    motor.

    We have BX metal cable in this building which is the local NYC code.
    The breaker panel has metal Greenfield conduit connecting to it with
    three wires entering the panel: white/red/blk. There is no green
    ground wire.
    Red connects to one side of the breaker terminal. Black connects to
    the other side of the breaker terminal. White goes to a seperate
    terminal, and I am assuming the white is thus neutral.

    Here are the meter readings I get when testing at the breaker panel:
    Blk/Red =209VAC
    Blk/Wht =120VAC
    Red/Wht =120VAC
    Wht/Service Panel = 0.29 VAC
    Blk/ Service Panel = 120VAC
    Red/ Service Panel = 120VAC

    ------------------------

    I will run BX cable from the service panel to an enclosed metal
    switchbox: and then from the switchbox to the motor. I am using
    10guage wire for the circuit.

    Questions:
    1) I need either a Duplex Breaker, or 2 Single Breakers to control the
    circuit. What should each pole of the breaker be rated at? Is 30amps
    suficient?
    2)Will a 230VAC single phase motor run OK on 210VAC service?
    3)The motor has 2 wires and a ground wire. From my understanding I can
    run the Red (120VAC) & Blk (120VAC) from the breaker panel to the
    switchbox, and then from the switchbox onto the motor. However, what
    do I use as a ground wire???
    If I put a copper grounding screw into the service panel and run a
    green ground wire off of that, it seems tat, hypothetically, if I get
    a short (ex., Blk goes to my green wire grounded to the service
    panel) it will conduct 120VAC.
    Am I missing something here?


    I have the current NEC codebook but am still perplexed.
    Thanks for any clarification.
     
  2. Rich Grise

    Rich Grise Guest

    1. Use a duplex breaker - if one side faults, you want to
    turn both sides off.
    2. Yes - these are "nominal" voltages - and if you've really
    got 2x 120, that's 240. :)
    3. The two motor wires are probably for black and red - don't
    even bother running a neutral, and ground it to the conduit/
    box. The neutral is grounded somewhere near the entrance panel;
    if you short one phase to ground, it _SHOULD_ pop the breaker;
    you could also look into a GFI Ground Fault Interruptor.

    Good Luck!
    Rich
     
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