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Thread: Motor Control Wiring

  1. #1
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    Motor Control Wiring

    Had a service call yesterday at a local dry cleaners for a compressor that wouldn't run. It turns out that the contactor/starter would not pull in. It was a 3-phase, 208V, 5HP motor with a GE starter. There was 208V single phase present at the coil but it wouldn't pull in. If you push in the contactor handle and held it the motor would start. I changed out the starter and installed this CH starter :http://pe.eaton.com/search/ECN0511EAA . Rewired the starter and threw the safety switch but motor wouldn't start. When I pushed in the handle the contactor held, the motor ran and shut down when the tank reached 120 lbs. However, the motor would not automatically restart. There is 208V at the coil.

    I'm thinking I mis-wired something or there is an internal setting that has to be changed for this unit to operate automatically. It seems pretty basic. There's a 2-wire external control switch in series with the air pressure switch. When the switch is turned on it is supposed to energize the coil and the pressure switch de-energizes the coil. Any thoughts would be appreciated.

  2. #2
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    How did you determine there was 208 at the coil terminals?
    Did you check the original coil for continuity?
    What is the voltage listed on the coil?

    Is this project related to your other thread and if so, how?
    Tom
    TBLO

  3. #3
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    Quote Originally Posted by ptonsparky View Post
    How did you determine there was 208 at the coil terminals?
    tested with a VOM
    Did you check the original coil for continuity?
    no
    What is the voltage listed on the coil?
    208V

    Is this project related to your other thread and if so, how?
    Not sure what other thread you mean but probably not.

  4. #4
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    Were you testing coil terminal to EG, then second terminal to EG, or terminal to terminal?

    Sounds like you may have wired the pressure switch in series with the holding contact, but that would not account for the voltage across the coil. Is there a pilot light in use?
    Tom
    TBLO

  5. #5
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    The ‘other thread’ was someone else’s. My mistake.
    Tom
    TBLO

  6. #6
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    Quote Originally Posted by ptonsparky View Post
    Were you testing coil terminal to EG, then second terminal to EG, or terminal to terminal?

    Sounds like you may have wired the pressure switch in series with the holding contact, but that would not account for the voltage across the coil. Is there a pilot light in use?
    Did not pull the wires off. Checked right at the coil terminals. No pilot light involved

  7. #7
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    It sounds like your seal-in aux contact is in series with the pressure switch.
    A compressor that runs start/stop via pressure switch needs to use 2 wire control (not 3 wire). I'm guessing it probably has a selector switch to turn it on/off, not momentary push buttons.

  8. #8
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    I think I might have figured it out. There is a factory installed jumper between the L2 and the # 96 terminal. There's a note at the bottom of the connection diagram that states Separate Control "Remove wire C if supplied and connect separate control lines to the # 1 terminal on the remote pilot device and to the # 96 terminal on the overload relay". I'll find out today and post it if I'm correct. Thank you all for attempting to help. The older I get the more brain cells I start to lose

  9. #9
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    Quote Originally Posted by goldstar View Post
    I think I might have figured it out. There is a factory installed jumper between the L2 and the # 96 terminal. There's a note at the bottom of the connection diagram that states Separate Control "Remove wire C if supplied and connect separate control lines to the # 1 terminal on the remote pilot device and to the # 96 terminal on the overload relay". I'll find out today and post it if I'm correct. Thank you all for attempting to help. The older I get the more brain cells I start to lose
    RTFM syndrome strikes again! It is not communicable but seems to strike everyone at some time or another.
    Tom
    TBLO

  10. #10
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    What still doesn't make sense to me is regardless of what may be mis-wired, if you measured 208 volts across the coil terminals, then the coil should be drawing current unless it is open circuited, and that would pull the armature in and close the motor contacts.

    Is possible you were not measuring directly across the coil and there is an open switch somewhere between your measurement points - such as the motor overload contact.

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