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Question on a size of Arc Flash

Discussion in 'General Discussion' started by Willis, Feb 19, 2009.

  1. Willis New Member

    Does anyone know what the results would be from a simple small distribution disconnect if it were short circuited and it had an arc flash. How large and destructive of an arc flash could this small of a device actually create?
    Willis, Feb 19, 2009
    #1

  2. Zog Well-Known Member

    Depends on the available fault current and the clearing time of the protective device. Could potentially be a devesating arc flash that can destroy the equipment and injure persons anywhere in the room, or could be very minor and not dangerous, all depends on the factors involved.
    Zog, Feb 19, 2009
    #2

  3. Noah Member

    For small disconnect switch, sometime it is hard to find space on the switch to put a lable on. How do you guys deal with those devices? What if you have a row switches on the wall for pump/motor control?
    Noah, Feb 19, 2009
    #3

  4. Willis New Member

    Clearing time

    What do you mean "clearing time"?
    Willis, Feb 19, 2009
    #4

  5. Zog Well-Known Member

    How long it takes the fuse or breaker to clear the fault at different fault current levels.
    Zog, Feb 19, 2009
    #5

  6. Willis New Member

    Thanks!

    I appreciate the information Zog.
    Willis, Feb 19, 2009
    #6

  7. Zog Well-Known Member

    Welcome to the forum.
    Zog, Feb 19, 2009
    #7

  8. WDeanN Well-Known Member

    How small is a small disconnect? If its fed by < 30A molded case breaker, it is likely to be < 4 cal/cm.
    If it's fed by a 600A drawout breaker at a unit substation, it could be > 40 cal.
    We actually have a case like this, where the breaker is used to feed several things, including a 70A 480V welding receptacle that is now >40 cal because they chose to feed it directly from the UnitSub.

    Noah, if there is a wire trough above the disconnect rack, I would consider putting the label there, although I have also covered the factory markings at times (I do my best not to, though.)
    WDeanN, Feb 19, 2009
    #8

  9. Willis New Member

    How small is a small disconnect? If its fed by < 30A molded case breaker, it is likely to be < 4 cal/cm.
    If it's fed by a 600A drawout breaker at a unit substation, it could be > 40 cal.
    We actually have a case like this, where the breaker is used to feed several things, including a 70A 480V welding receptacle that is now >40 cal because they chose to feed it directly from the UnitSub.


    What is the cal/cm range that an arc flash becomes deadly or cause serious injury?
    Willis, Feb 19, 2009
    #9

  10. Zog Well-Known Member

    1.2 cal/cm2 will cause second degree burns in 1/10th of a second. Put you in a burn unit, life changing event.
    Zog, Feb 19, 2009
    #10

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