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Arc flash and explosion caused by incorrect trip set point on breaker

  • What happened?

    “Before racking out a 4160 volt upstream breaker, I was trying to trip out a 480 volt, 1200 amp main breaker.

    I was standing on the hinged side of the door trying to push the trip.

    On the third attempt, it exploded and kept exploding for 30 seconds.

    The fire ball sprayed sparks and molten metal on my colleague. He reacted quickly and escaped through the back door.  I crawled out from underneath the smoke. We were in shock and received first aid.

    I’ve never been so happy to be able to hug my family as I was that evening.”

    Burn marks left on equipment from an explosion
  • Why did it happen?

    The 4160 volt breaker’s trip relay had an incorrect trip set point, so the incoming feeders were left energised.

    The buss bar connecting the two breakers (4160 volt and 480 volt) had blown and melted open.

    Why did it happen - icon
  • What did they learn?

    “If I had been standing on the other side of the door I would have been badly injured or killed.

    This has happened to us before, so we always expect the worst when doing switching.

    We take every precaution to make sure everyone involved is out of harms way – because we never know when a breaker may malfunction, and you may never get a second chance.

    One second of complacency could have changed my life.”

    What learn - icon
  • Ask yourself or your crew

    What other actions could have been taken?

    How can something like this happen here?

    Have you ever been complacent when switching, tripping or racking out (or when working around electricity)?  Share your experiences.

    What precautions have we put in place to:

    • Reduce the likelihood of arc flash or other events?
    • Reduce the severity and consequences of arc flash or other events?

    What other barriers/safeguards can we put in place?

    Ask your crew - icon
Published on 13/05/19 26 Views 0 likes

An arc flash explosion was caused by an incorrect set point on a breaker. The fire ball sprayed molten metal on a worker. Luckily no one was seriously hurt.