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Thread: What the difference between a lighting contactor and a relay ??

  1. #1
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    What the difference between a lighting contactor and a relay ??

    What is the differences beteween a lighting contactor and a relay contactor???

    Are the lighting contactors more robust?? durable??

    Are enerizing coils quieter??

    Can you interchange the two?? I have often used a normal relay for lighting controls, can I use a lighting contactor for motor controls???

    Thank you for you time Dennis

  2. #2
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    I was taught that they both served the same function except that they were consider relays up to 10a and contactors above 10a.
    But from practical experience that definition doesn't work at all. I believe that electrically they do basically the same thing.
    I started to dig a little but haven't been able to quickly sort it out but I am strongly suspect that it may be found in the UL listing of the devices and the testing requirements. I would be concerned about how the relay is being applied and if it is UL listed for the application. There may be an ussie with withstand ratings should there be a fault down stream.
    I suspect that relays are not made as robust and a lighter in construction which may allow them to be faster. If that's a big advantage I'm not sure if that is of great importance in an general application or not.

  3. #3
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    I thought that a lighting contactor was only listed for lighting applications, but that a relay, or a general purpose contactor could be used for any application within its rating.

  4. #4
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    Quote Originally Posted by rt66electric View Post
    What is the differences beteween a lighting contactor and a relay contactor???

    Are the lighting contactors more robust?? durable??

    Are enerizing coils quieter??

    Can you interchange the two?? I have often used a normal relay for lighting controls, can I use a lighting contactor for motor controls???

    Thank you for you time Dennis
    A lighting contactor is a specific case of a relay.

  5. #5
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    It is in the listing / testing requirements. "Relays" are intended for "Pilot Duty", meaning they are not expected to switch loads with high inrush and/or low power factor. "Contactors" are, plus contactors have a higher expectation of over load capacity. Relays on the other had are expected to be capable of a much higher duty cycle than contactors, and a typical relay electrical life span for the contacts is 10 million operations, where a contactor would be 1 million. So it's a trade off.

    In contactors, the difference between a lighting contactor and a motor contactor is mostly just the ratings of the contacts; the same set of contacts will show a higher amp rating in a lighting contactor than in a motor contactor. So you can always use a motor contactor for lighting, but not the other way around unless you derate it, and unless the mfr shows the motor switching rating, you have no way of knowing by how much. There are also latching contactors for lighting, something you would never do for motors and with some electrically held lighting contactors, the coils are made to be extra quiet in case they are mounted in a living space. You don't want coil hum to be amplified by walls. That makes the coils a little more expensive to make. Because motor contactors are usually controlling noisy machines anyway, nobody worries about that.
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