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A switch on 3-phase

  1. Jul 3, 2008 #1

    How do you switch a 3-phase circuit on and off? Is it possible to put a relay on just one leg of the phase, or do you need to somehow switch all 3 at the same time? In industry, what do they use to switch 3-phase circuits, for instance, with a push button start/stop?

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  3. Jul 3, 2008 #2


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    You definately need to switch all three at once.
    since three phase is generally used with failry beefy supplies you tend to have a controller switching them from an electronic switch rather than a simple mechanical switch.
  4. Jul 3, 2008 #3


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    A 3-phase relay or contactor: http://www.allaboutcircuits.com/vol_4/chpt_5/2.html

  5. Jul 3, 2008 #4


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    You weren't very specific, triden, but there are plenty of switches out there that are simply three single pole switches mechanically linked together. Any ordinary circuit breaker can have a peg inserted between it and its neighbors to make such a switch, for example. Larger ones are specially made with 3 poles, but function the same. You can get relatively ordinary circuit breakers probably up to a few thousand amps at a few thousand volts. Grainger stocks them up to 1000A at 600V.
    Last edited: Jul 3, 2008
  6. Jul 3, 2008 #5


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    Last edited by a moderator: Apr 23, 2017
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