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Thread: Closing a CB for the first time

  1. #1
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    Closing a CB for the first time

    When our guys close a 480V (or sometimes more) CB or switch for the first time, they always gear up in arc-rated PPE. It got me wondering: How often do they flash the first time they're operated, and why? Our guys say they've heard of it happening, but I don't know anyone with direct knowledge of it. Manufacturer's defects seen unlikely, given the testing these things undergo before they're put under load. A couple of the guys suggested they blow up because tools and debris might have been left in them during installation. Thoughts?

  2. #2
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    Operator error, someone goofed up on installing load conductors would be my first thought. I have had factory internally miswired items fail.
    IMO, they are doing it correctly, for whatever the reason.
    Tom
    TBLO

  3. #3
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    I would also never stand in front of a breaker or safety switch when closing it.
    Tim
    Master Electrician
    New England
    Yesterday's Technology at Tomorrow's Prices

  4. #4
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    You may need to refer to electrical accidents statistics for a calculation of risk of arc flash involved in operating the breaker for the first time.

  5. #5
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    Quote Originally Posted by tkb View Post
    I would also never stand in front of a breaker or safety switch when closing it.
    Why? Do you know of anyone who's had one blow up? Or just being cautious?

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    If all covers are in place, there should be no requirement for PPE and no more risk than that of getting struck by lightning on a sunny day. The only caveat would be a true bolted fault on a breaker who's AIC rating was calculated so incorrectly that the hedge factors in everything are overcome.


    I know what I don't know, and I know where to go to find it!

  7. #7
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    Never in my career have I seen a brand new circuit breaker in the box in the closed position. Except that one time...

    And this wasn't bought from a big store where people just manhandle things and put them back on the shelf. This was in a pallet of goods shipped overseas to a project I was working on in Colombia. Thank goodness it was only a 3-phase 208V panel, in the electrical room of a 5-story residential complex (90 rooms plus multi-purpose rooms on the bottom).

    So it was already near the end of the day (may have been the last breaker) and I took it out of the box and pushed it onto the bus. My three fingers were on the three screws, and it lit me up. My hand was numb for three days.

  8. #8
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    Quote Originally Posted by wtucker View Post
    Why? Do you know of anyone who's had one blow up? Or just being cautious?
    I had a motor starter blow up when I turned on the power.
    The cover blew off and dented the duct about 8’ away.
    If I were standing in front of it, I would have taken the hit and flash.
    Tim
    Master Electrician
    New England
    Yesterday's Technology at Tomorrow's Prices

  9. #9
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    Look up FPE, anything can happen and I too never stand in front, have safety glasses, earplugs on.

  10. #10
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    Even for residential panels I always stand off to the side and use the door as a shield when flipping on a breaker. I avoid turning on a breaker with the cover off if I can. I carry level 1 arc flash gear in the truck and put it on when pulling and replacing meters.

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