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Wiring up an Air compressor using a Contactor

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  • Wiring up an Air compressor using a Contactor

    This question came up recently. I thought it might be appropiate here.

    Wiring a magnetic contactor switch: Grainger 5B111 (Square D Two pole open type with 240 V coil) To control an air compressor
    The incoming 240V (from the circuit breaker) connects to terminals 1 & 3 Labeled 1L1 & 3L2
    Take the wires loose from the pressure switch that run from it to the motor and reconnect them to terminals 2 & 4 Labeled 2T1 & 4T2

    The coil/control circuit starts by running a small jumper wire using spade terminals from 1L1 to one side of the coil. Run a wire from the other side of the coil to one side of the pressure switch. A wire from the second contact Same side of the pressure switch runs to the spade terminal on 3L2

    (This part may be a little confusing but what you are looking for is to connect these two wires when the pressure switch closes and to open the circuit when the pressure switch opens. It doesn’t matter which side of the pressure switch you use, just make sure that closing and opening the pressure switch opens and closes the circuit from the coil.)
    Byron Boucher
    Burnet, TX

  • #2

    I forgot to mention that an on off switch to deactivate the compressor can be inserted anywhere into the coil control current path. Grounds should be tied together and to the incoming ground.
    Byron Boucher
    Burnet, TX