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Thread: 3 Phase motor foward/reverse with cam switch

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    3 Phase motor foward/reverse with cam switch

    Hi All

    I have a machine that uses a 1hp 3 phase motor wired into a 3 position cam switch (forward, off, reverse)
    When i run the machine in forward and then toggle it thru the "off" position into the "reverse" position it carries on running in the forward direction.
    If i let it come to an absolute complete stop before i engage the reverse position then it usually works fine and runs in the opposite direction, but not all the time.
    I have tried swapping the phases around on the supply side but it does the same thing (although reverse now = forward and visa versa)
    I know i have come across this before and cant remember what the remedy is.
    Anyone know the answer?

    Thanks

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    Diamond Member Justloadit's Avatar
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    Sounds to me like there is a faulty contact on the reverse position side of the switch, as the motor continues turning on 2 phases. It also means the motor is over rated for the application, as the load seems to have no effect on the motor shaft, or else it would have burnt out by now.
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    Diamond Member AndyD's Avatar
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    Sounds very odd, usually 3-phase motors have good starting torque in either direction depending on which way around the supply is connected.

    Is the current draw on all three phases the same when the motor supply is connected?
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    Ya you guys are on the money, in reverse the one phase was drawing considerably less current than the other two. Turned out to be a faulty contact on the reverse side.
    Lekker, thanks for the help!

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