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Thread: Three Phase Size 1 Starter for 120V Single Phase motor ??

  1. #1
    Join Date
    Jan 2008
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    7

    Three Phase Size 1 Starter for 120V Single Phase motor ??

    I intend on using a Three Phase Size 1 Full Voltage Non-Reversing Starter to power up a 120V Single Phase pump motor (1/3HP). I intend on using two of the poles on the Three Phase Breaker and two of the poles on the Contactor for the connection. I also intend on not using the CPT and hooking up the control wiring (120V) of the starter directly to the each phase leg. Will this cause any malfunctions in the operation of the Breaker and/or the Contactor? Does anyone know of any issues that may affect the proper operation of this setup?

  2. #2
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    If the coil is rated for the voltage..because it sounds like when you apply power you will pick the starter up and the item will run until you through the disconnect..Is that correct..Why do it that way if you want it to run when you turn on breaker..you could get the same with a breaker and disconnect and save cash..
    Life is temporary, heaven is forever. live life like it is your only chance to make a difference..

    to do nothing is the surest way to achieve nothing..

  3. #3
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    Most starter instruction sheets that I have seen show bringing one of the output wires (after the overload) back into the 3rd phase input, not just using 2 of the 3 poles.

    I also intend on not using the CPT ...
    I too don't understand this.

  4. #4
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    Motor Connection

    Quote Originally Posted by mrrjw
    I intend on using a Three Phase Size 1 Full Voltage Non-Reversing Starter to power up a 120V Single Phase pump motor (1/3HP). I intend on using two of the poles on the Three Phase Breaker and two of the poles on the Contactor for the connection.
    If the motor is 120V as you say your described connection will burn it up. Is the motor actually 240V? I am a bit confused by your control discription but if the motor is 120V or 240V and you have no remote control requirement why not use a single-pole or two-pole breaker and install a manual starter?

  5. #5
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    Quote Originally Posted by justdavemamm
    Most starter instruction sheets that I have seen show bringing one of the output wires (after the overload) back into the 3rd phase input, not just using 2 of the 3 poles.
    This method is normal for electronic and IEC style overload realys because they are often supplied with "phase sensitivity" which cause the relay to trip faster on single phase loading. But if the motor is lightly loaded then this early trip feature is not much of an issue. And this feature is nowhere as sensitive as an phase loss relay.

    Traditional NEMA starter overload relays do not contain this feature so they do not need special wiring.

    The primary reason for control power transfromers is so control circuits can operate at at 120V or less rather than at line voltage. So if the line voltage is already 120V, there is no overwhelming reason to include a CPT.
    Just because you can, doesn't mean you should.

  6. #6
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    Well, heck, why not just use a single-pole switch and, if the motor requires, a fuse?
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  7. #7
    Join Date
    Jan 2008
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    The reason we are using a FVNR NEMA 1 Starter on this 120V 1-phase application is because the application necessitates DCS control of the motor start/stop. This is a Chemical Injection skid where the DCS has to monitor the process and inject the necessary chemicals when needed. A simple Fused Disconnect or Breaker cannot be managed as such.



    Thanks to everyone for their valued input!

  8. #8
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    May 2005
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    21,838
    Quote Originally Posted by mrrjw
    The reason we are using a FVNR NEMA 1 Starter on this 120V 1-phase application is because the application necessitates DCS control of the motor start/stop. This is a Chemical Injection skid where the DCS has to monitor the process and inject the necessary chemicals when needed. A simple Fused Disconnect or Breaker cannot be managed as such.
    Well, of course.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  9. #9
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    ahh see what you learn with more info..I see no reason why it wont work..little over kill though but situation calls for over kill maybe..
    Life is temporary, heaven is forever. live life like it is your only chance to make a difference..

    to do nothing is the surest way to achieve nothing..

  10. #10
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    This starter will work fine controlling a 1PH 120V motor. You'll only need 1 of the poles. The 120V neutral goes straight through, it need not be connected through a starter pole. It will need to be tapped (wirenut), and landed on the overload switch. (Where the grounded side of the CPT goes now.)

    The CPT is not needed, and if fact likely cannot be used anyway. It likely has primary taps for 240/480 only. Simply tie your 120 control voltage to terminal #3, or the hot side of the coil.

    You'll likely need to install all 3 heaters, or (depending on brand) the overload relay might not reset.

    The flow of control power is as such; from the source (switch, PLC, etc.), to terminal #3. This source must be maintained for as long as the motor is expected to run. There's a wire from term #3 to one side of the coil. The other side of the coil is wired to the overload contact. (N.C.) The other side of this contact goes to the 120 neutral. Yes, the overload relay breaks the neutral, that's just the way starters have been wired for the past century or so.

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