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Closing a CB for the first time

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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
    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

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      #3
      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

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        #4
        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.

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          #5
          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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            #6
            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!

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              #7
              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.

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                #8
                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

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

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                    #10
                    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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                      #11
                      When the load wiring is new (service change, new circuit, etc.), I routinely use my solenoid tester between a line-side hot and each load terminal to make sure that no load conductor is grounded before energizing.
                      Master Electrician
                      Electrical Contractor
                      Richmond, VA

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                        #12
                        The only time I've been exposed to a serious arc flash event was when someone closed a breaker for the first time. I was working on a panel with a 600HP soft starter in it and I finished, so I told the guy in the other room that I was done and I started to close the doors of the panel. Just as the local disconnect handle interlock engaged with the door, he closed the breaker in the switchgear feeding the soft starter. The local disconnect was open, but they had nicked a LINE SIDE conductor in the conduit and it vaporized, blowing a fireball out at me. Because the doors were almost closed and the interlock held, the blast was deflected mostly up and down so it torched my boots and singed my eyebrows and hair where the safety glasses didn't cover. I did NOT, by some miracle, wet myself... Ever since then I always stand to one side rather than directly in front of anything.

                        In the investigation as to how that nicked conductor was allowed to be there, turned out they meggered everything, then pulled the conductors BACK into the conduit in order to remove and re-install the back panel for the soft starter. But they failed to re-megger the conductors again, ASSuming they were OK after being pulled back into the conduits.
                        __________________________________________________ ____________________________
                        Many people are shocked when they discover I am not a good electrician...

                        I'm in California, ergo I am still stuck on the 2014 NEC... We'll get around to the 2017 code in around 2021.

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                          #13
                          Originally posted by Strathead View Post
                          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.
                          That is a false statement unless the enclosure is arc rated

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                            #14
                            I suppose there may be some increased chances of a fault from miswiring or bad equipment that "first time", though there is still risk anytime you turn it on. Even after there has been some kind of repairs done that risk may be a little higher the first time afterward. Testing for faults before turning on "the first time" should lower the chances, if you find and fix any faults indicated in the testing.

                            Even on low incident energy applications (maybe typical dwelling or small commercial project) how often do you find something is faulted the first time you energize a circuit? Maybe not all that many times for most of us, but sometimes the fault isn't something we did but rather a defect in something and we never noticed until energizing it.
                            I live for today, I'm just a day behind.

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                              #15
                              Originally posted by zog View Post
                              That is a false statement unless the enclosure is arc rated
                              Can you quote a source that requires PPE when all covers are in place?


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

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