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Thread: Arc guards

  1. #1
    Join Date
    Nov 2007
    Location
    Mississippi
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    1,356

    Arc guards

    What is the purpose of the metal squares underneath the cover of three pole contactors? I have heard them called arc guards. I know a lot of people throw them out the first time the points are checked.

  2. #2
    Join Date
    May 2000
    Location
    Stafford, Va. USA
    Posts
    213
    Hi Socotech,
    They are arc guards or also called arc chutes. Their purpose is to give a path to the arc that is created from the inductive "kick" when the contactor opens. They are there for safety purposes.
    The inductive kick is a result of an electrical property called inductance, a property caused by any electrical load that has windings, motors, transformers, etc. Inductance tries maintain current flowing in a circuit when the contactor opens. Of course, when the contacts are open enough, the current cannot maintain flow.
    Again, the arc guards are a safety feature to capture the arc of each phase, to keep them from meeting each other.
    I hope this helps.
    Allen
    UA Local 602
    A man who says that he can't learn anything in a class is exactly right.

  3. #3
    Join Date
    Jul 2007
    Location
    The Hot South
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    1,325
    Quote Originally Posted by socotech View Post
    I know a lot of people throw them out the first time the points are checked.
    Why would someone throw them out? They're there for a reason.

  4. #4
    Join Date
    Nov 2007
    Location
    Mississippi
    Posts
    1,356
    Too lazy to put them back when they fall out.

  5. #5
    Join Date
    Jun 2012
    Posts
    529
    They always piss me off when you try to be careful and they fly allover. Like R123 said they are there for a reason so I collect them all up and put them back in. One of our managers told us to leave the covers off contactors so we can inspect them faster on service checks (what a joke).

  6. #6
    Join Date
    Jul 2000
    Location
    Dallas,Texas
    Posts
    4,963
    The possibility\ probability of a phase to phase short goes way up with the arc shields removed. That is especially true at 480 Volts.
    When the contacts try to pull off, the bigger arc is created because the contacts were carrying a load. I have seen contactors burned up from the combination of arc shields removed and a low humidity day.

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