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Witnessed an arc flash today on a 1200A distribution panel

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  1. SecondGen's Avatar
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    Witnessed an arc flash today on a 1200A distribution panel

    I was doing an infrared scan for an electrical contractor on a 120V 1200A distribution board, and as they were closing up the front cover, one of the panel screws was drilled into a feeder cable that was sitting against the enclosure.


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    The resulting fault was pretty loud and there was a small fireball but thankfully nobody was hurt and everyone was wearing their PPE. The flash happened with the cover partially screwed on and the incident energy was somewhat contained.


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    Other than some burn marks and smoke damage inside the panel, everything was easily repairable. The cable and surrounding edges was wrapped with some rubber splicing tape around the flash site and everything was good to go.


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    Amazingly there was no service interruption, which was good because this distribution panel was feeding multiple emergency panels throughout a health care facility. The screw acted as a fuse and melted before the main upstream breaker could trip, you can see in the photo how long it was originally.


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    I wanted to share this story to serve as a reminder that things like this always happen when you least expect it. Stay safe out there.

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    Nice. That is one of my biggest fears with IR scanning. Itís not often that we get to scan new equipment. Most times itís old equipment and the old panels are not the best to mess with. Over time we have seen panels evolve and become easier to open up while in service. But having a new panel isnít justified if the craftsmanship isnít the greatest. Craftsmanship can make a new panel even more dangerous to open than an old panel. Older panels could have 30+ years of ratty work done to them.

    Just something to think about

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  5. jdptech is offline Junior Member
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    This is the second time I've heard of this happening...

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    Quote Originally Posted by ElectricalTestTech View Post
    Nice. That is one of my biggest fears with IR scanning. Itís not often that we get to scan new equipment. Most times itís old equipment and the old panels are not the best to mess with. Over time we have seen panels evolve and become easier to open up while in service. But having a new panel isnít justified if the craftsmanship isnít the greatest. Craftsmanship can make a new panel even more dangerous to open than an old panel. Older panels could have 30+ years of ratty work done to them.

    Just something to think about
    To tag onto that, the claw designs on a lot of the older Panels always keeps me on edge. Between them only grabbing half of the time and then when they do you have to worry about pinching wires. Almost gave an apprentice working with me and another guy a heart attack when a claw grabbed a circuit and blew it out right next to him.

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    Quote Originally Posted by jflan13 View Post
    To tag onto that, the claw designs on a lot of the older Panels always keeps me on edge. Between them only grabbing half of the time and then when they do you have to worry about pinching wires. Almost gave an apprentice working with me and another guy a heart attack when a claw grabbed a circuit and blew it out right next to him.
    Yes, the older claw designs are ticking time bombs, especially the ones with no feet. I've seen circuits get blown many times.

    It can't be stressed enough how mindful we must be when putting these older covers on and off. The very worst is when a wire gets pinched in a way that it blows when the next guy goes to take the cover off.

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    Quote Originally Posted by SecondGen View Post
    Yes, the older claw designs are ticking time bombs, especially the ones with no feet. I've seen circuits get blown many times.

    It can't be stressed enough how mindful we must be when putting these older covers on and off. The very worst is when a wire gets pinched in a way that it blows when the next guy goes to take the cover off.
    The one site I have worked a for a couple of year started removing the claws, gluing the screws in place, and drilling new holes. It can be time consuming when you are trying to get it done the first time, but the next year I went back we got everything done in half the time.

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    Quote Originally Posted by jflan13 View Post
    The one site I have worked a for a couple of year started removing the claws, gluing the screws in place, and drilling new holes. It can be time consuming when you are trying to get it done the first time, but the next year I went back we got everything done in half the time.
    Huge help, for sure. Another thing I've seen is drill/tap a hole top center and run a screw from the inside out, this gives you something to hang the cover on while you work the claws.

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    Quote Originally Posted by SecondGen View Post
    Huge help, for sure. Another thing I've seen is drill/tap a hole top center and run a screw from the inside out, this gives you something to hang the cover on while you work the claws.
    That would be extremely useful. I have seen guys do that on large panels without feet.

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    Thank you for posting this. I recently started doing IR and needed the lesson in the "what if's". The company I work for has been offering to install IR port holes for later viewing when we have the panels off for circuit breaker testing etc. I'm not sure if many places are spending the money, but everytime I see a panel with these portholes, it makes you think how much safer it can make IR work.

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