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  1. #1
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    Nov 2014
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    3 phase monitor mechanical style

    Ever have a motor that single phased and burnt up. Well get a 3 pole 24 v contactor. If u lose leg to transformer ur good anyway then use a 230 v coil relay and use power legs to motor for coil then jumper to both commons and then normally open to contactor. Lose a leg to coil relay takes out both legs and if u make sure the power wire to transformer is the third leg u should be good

  2. #2
    Join Date
    Dec 2012
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    Quote Originally Posted by Caleb Brunson View Post
    Ever have a motor that single phased and burnt up. Well get a 3 pole 24 v contactor. If u lose leg to transformer ur good anyway then use a 230 v coil relay and use power legs to motor for coil then jumper to both commons and then normally open to contactor. Lose a leg to coil relay takes out both legs and if u make sure the power wire to transformer is the third leg u should be good
    Have you tried it? Im thinking if its a delta configured motor you will probably pull power thrue a winding and prolly chatter or burn up a contactor. Should work with a Y setup though.

  3. #3
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    Thread Starter
    It wasn't exactly like that but I've made them before I think I used a few more components. And your right that would pull amperage through the coil of the relay but I took time and drew it up uing the diagram but it has worked everytime.

  4. #4
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    Thinking bout it a y would do exctually the same

  5. #5
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    Thread Starter
    OK if u lose either leg to transformer u lose coil voltage to contactor and use third leg as a constant power supply to relay coil just from the incoming power and when contactor pulls in it gives relay 230 coil voltage that makes no close giving it all three legs. So if one leg to relay coil goes out so does power wire going through relay. If either leg to transformer goes out contactor opens. So you never have 2 hot legs on motor. Could go further and make signal to contactor go through another relay that gets power from single wire from other 230v relay and all three legs die each time one does. This is on 3 phase commercial package units of course. So when ur condenser fan is told to.come on it has to make third leg and third leg has to make to give relay power to keep monitor contactor closed. This is after control to fan but before power reaches fan. If leg on contactor burns out guess it could still single phase unless u wanted more relays. But we had a 3 phase motor that went out like 3 times so we did this. It was fun. U can buy one and it tells u what leg died and prolly cheaper n better lol. But who has time for supply house. If I had paper I'd draw it in no time.

  6. #6
    Join Date
    Aug 2010
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    Phase protective relays. They've been around for a long time.

    http://static.schneider-electric.us/...013-008-89.pdf

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