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Manufacturer
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11 Posts
Discussion Starter #1
We all know the dangers of Arc Flash, but sometimes it's easy to forget that it can happen to anyone!
Have you ever been involved in, or witnessed, an Arc Flash related incident during a job?
If so, help remind your fellow electricians to stay alert by sharing your stories below.
 

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Old Grumpy Bastard
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61,086 Posts
Never been involved myself but had a friend killed and his son badly burned years ago.
 

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Banned
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39,722 Posts
We had a standard 480-277/208-120Y Xformer in a 'lectric room ,25k iirc, worked the day before, blew like a truckoad of roman candles on me turning it on the next day, think camera flash X1000

I was instantly blinded , fell to the ground, and resorted to the right hand search i was taught in nozzlehead school to find the door out.

My vision returned after about 5 minutes , but it was not a pleasant 5 minutes

The manufacturer conceded a defect after investigation....

~C(old, not near as bold)S~
 

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Bilge Rat
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7,020 Posts
2 incidents come to mind.....

1) I wasn't there but had to deal with the results. Geothermal power plant, 30 MVA generator operating at 13.8KV and paralleled to the grid. This unit had surge capacitors mounted inside the high voltage terminal box. The box was about 4' X 4' X 3' and made from 1/4" steel. The cover was 3/16" steel.

When I arrived, the cover (4' X 4') was laying about 100' from the box it was attached to, it used to be flat, now it was C shaped and the 3/8" holes for the bolts were about 3/4" where it had ripped through the bolts.

The surge capacitors blew up causing all 3 phases to arc over to each other and to ground. Given both the gen and the grid contributing to the fault, there was a pretty fair amount of energy available.......

2) Two geothermal plants that had about 12 miles of overhead line connecting them together. They could both operate without the tie line. No other loads on the tie line. 12.5 KV with vacuum circuit breakers on one end, a 12.5 - 4160 transformer on the other.

They decided to energize the line one day, both ends were open. A line like that will very likely have some pretty serious induced voltage on it especially given the dry climate around here. I suggested closing the 4160 transformer first but being just a dumb journeyman I was pretty much laughed at.

The switchgear was about 40' long and inside a building. The breaker control switches are on the from of each breaker cubicle. I closed the tie breaker in and instantly the generator breaker tripped. Then there was a loud buzzing sound behind the main broker cubicle and dense smoke began pouring out. This is where the incoming power is landed, 6 parallel 1000 MCM 15 KV cables that went to a 45 MVA transformer about 100' away. Lots of energy here......

The high side of the transformer had an SF6 breaker but the control switch was in a panel directly behind where the smoke was coming from. No way was I going there....... The other control switch was in a meter house about 200' away. I doubt if it took me a whole second to get there......lol.

The induced voltage from the O/H line caused enough of a surge that it took out the surge capacitors in the incoming main cubicle. Hence the arcing and smoke. It also got the surge capacitors at the gen but because the gen breaker tripped quickly, not much damage there.
 

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Modérateur
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8,693 Posts
I have couple of arc blast on my side so a quick summary on it.,


1) 480 volts transfer switch exploison because when I got there I did check the proper voltage and phase sequinice and the generator size is 3 MW diesel driven.

anyway.,, I manged to change source from uility side to genrator side it work just fine but once the load test was done with the generator and somehow I was not aware that the power company just kick on their capatitor bank on same time as I switch back to uility side and it blew the transfer switch out and tripped the uility side out but manged to get back on generator power by second set of transfer switch and I learn later somehow the capaitor bank did shift the phase some just enough to get the effect of two different phases sequince out of sychronous.

The damage did blew the transfer switch door off and that is pretty thick steel I think it was about 32 inch wide about 4 feet tall if I recall it correct.

That was ran from remote control but the blast was loud enough for anyone to get their ears ringing for a while.

2) 480Y277 volt breaker failure. that time I was called in to investage the loss of power of that circuit and I verify it to make sure the load side of breaker is compelty dead or deengerized which I did test with two different meters and it say nada or zero volts. then as soon I hit off postion the breaker blew up which it got me by suprise and got hit from flying fragments.

later I found out why one of the concants was slipping as soon I swing open I am not sure if the dust or something inside the breaker have flashover thru the opening. plus the bussbar connection to breaker is bad.

replace the whole panelboard.
 

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Registered
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59 Posts
On a hot summer day I went outside my building to watch a low black cloud approaching. Just as it passed overhead it unleashes a lightning bolt onto the transformer pad. As I was only 30 feet away it was an experience I'll never forget.

Next a couple guys come out to advise me the building is dark so over to the ancient FP gear I go and see the 2,000 A main tripped. The gear is 5 cabinets with the main on the right (cabinet 5) so I stood off to the far right and threw the main. As it closes cabinet 4 explodes. It had two large vacant breakers, one just disintegrated, the other burned to charcoal.

Got lucky twice that day, the second time in spite of my own stupidity! Wear the gear!
 

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Banned
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39,722 Posts
We exist in a dangerous trade, literally working on potential bombs all day.....

they should take the noobs in apprenticeship school outside, and blow some gear up for them

jhmo

~CS~
 

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Modérateur
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8,693 Posts
We exist in a dangerous trade, literally working on potential bombs all day.....

Chicken Steve.,,

I agree with you and yes it is dangerous if you are not prepared.

they should take the noobs in apprenticeship school outside, and blow some gear up for them

jhmo

~CS~
Maybe so CS.,,

but I will keep a good reminder for anyone I dont care if noobs or old schoolers .,,,
But one basic rules it always come in your mind .,,

Always.,,,,,,,,

EXPECTED THE UNEXPECTED

and work safe so we can go home to the family or freinds.
 

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Banned
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39,722 Posts
Grand advice FrenchOne...:thumbsup: and i can equate it to a long history of car accidents , always the ' i didn't EXPECT the other car blah blah' .....

~CS~
 

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Bilge Rat
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7,020 Posts
Another one I didn't see happen but had to clean it up.

Generator van for a portable hot plant (asphalt plant). A hot plant has a hot oil system that needs to be kept energized 24/7. It can handle a shutdown for an hour or so but not all night.

The gen van is a 40' semi trailer with a 2000 KVA gen sitting lengthways and a 45KVA unit sitting crossways in the very front. Both gens have breakers w/shunt-trips. The big gen has a speed switch, it's in the 'idle' position when the gen is not running and when it's warming up. The 'idle' position will shunt-trip the big gens breaker.

When the switch is placed in the 'rated speed' position, it shunt-trips the small gens breaker. There is no paralleling gear and the breakers are closed by hand.

The small gen burnt up its breaker and the plant guys replaced it.

When I got there, the small gen was laying on its side in the front of the trailer. The replacement breaker had a shunt-trip but it was 120AC. The system was 24DC so placing the speed switch to 'rated speed' did not shunt-trip the small gens breaker. Closing the big gens breaker certainly tripped it though........lol.
 

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Manufacturer
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11 Posts
Discussion Starter #12
Thanks for sharing these stories. We can always learn from each other when it comes to safety, but we know that training and preparation are also key components to preventing these occurrences.
If you want a refresher, or just want to see if you are up to date on the latest arc flash strategies and other product training, you can reference our NEC Resources and the Apprentice Library, available on our Square D Contractor Portal. If you're new to the Square D Contractor Portal, you can register here.

Thank you for all you do to keep your communities running safely and smoothly!
 

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Registered
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507 Posts
Saw my journeyman get burned closing a 60A 600V molded case breaker into a bolted short at the other end of the cable. Blew up the breaker and some of the arc escaped around the handle and burnt his hand. He was back at work in a couple days but was a good warning for the whole crew to be careful even with equipment we tend to be cavalier around.
 
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