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Thread: Motor wiring diagram

  1. #1
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    Motor wiring diagram

    I have a 3HP 3phase 230/460V motor for a through the wall exhaust fan.
    The wiring diagram shows 2 red wires labeled t-stat.
    Under the diagram it says "Use a manual momentary start switch only".
    I've not seen this before and am unsure what to do.
    Does that mean it can't be line started?
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    Tony Hill

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    Here's the nameplate.
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    Tony Hill

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    The "J" leads are usually internal thermostat leads used to shut down the motor on high winding temperature. I am not sure about the "manual momentary start" comment. I think they are looking for a motor starter with a three wire start stop circuit. The "J" leads would be connected to the control circuit to drop the starter out on high temperature. The word "manual" in that comment does not make a lot of sense to me.
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  4. #4
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    I'm guessing they want a momentary push button so that in the event the motor windings get hot enought to trip your control circuit, it can't be automatically started again and damage or further damage the motor. It would take you pushing the momentary push button to start it again.

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    Quote Originally Posted by dkailiuli View Post
    I'm guessing they want a momentary push button so that in the event the motor windings get hot enought to trip your control circuit, it can't be automatically started again and damage or further damage the motor. It would take you pushing the momentary push button to start it again.

    Ah, that makes sense. Can anyone verify?
    Tony Hill

  6. #6
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    Yes, that's exactly what it means. What they are saying is that this is an internally protected 3 phase motor, something not common in industry, and it therefore does not require an external overload relay be used with a contactor (or manual motor starter) that will not automatically reset. Or put another way, you could theoretically use this with just a 3 pole contactor operated by a selector switch or toggle switch with the t-stat in series with the coil, not a full blown motor starter. But if you do, the control switch remains closed so the t-stat will cool down and allow automatic restarting too soon and apparently this motor is not rated for that. Somewhat common in motors designed for specific applications, like OEM vent fans for example. If you notice, this motor is not UL listed, it is a UL Recognized component, which means whomever uses it must get the ENTIRE machine and control system listed after assembly, and that control requirement will need to be part of the scheme.
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  7. #7
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    Jeff,
    So in this case "manual" means a non-automatic restart of the motor?
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  8. #8
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    Quote Originally Posted by don_resqcapt19 View Post
    Jeff,
    So in this case "manual" means a non-automatic restart of the motor?
    Right. If it over heats, a human is required to intervene.*


    * thereby accepting blame for the fire when he ignores common sense and resets it anyway.
    __________________________________________________ ____________________________
    "Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
    — Kilgore Trout (via Kurt Vonnegut)

  9. #9
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    *
    Last edited by Jraef; 07-12-12 at 12:15 PM. Reason: Posting glitch, duplicated
    __________________________________________________ ____________________________
    "Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
    — Kilgore Trout (via Kurt Vonnegut)

  10. #10
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    Okay, so the only thing the plans call for on my part is a disconnect.

    There was nothing in the instructions about doing anything with the t-stat wires, so I believe my responsibility ends with wiring the motor from the disco.

    Is there anything wrong with just starting the motor with the disco?

    This is in an auto shop and I don't think a restart button at the disco would be a wise choice. The mechanics would just hit the reset and never say anything to anyone. It would be better if it takes some effort to restart.
    Tony Hill

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