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 Post subject: Arc Flash Experiences
PostPosted: Tue Nov 03, 2009 1:56 pm 
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Joined: Fri Jan 16, 2009 1:07 pm
Posts: 67
Location: North Florida
I’m taking an informal poll of everyone on the forum about injuries due to arc flash. Please provide a brief description of any injuries of which you have direct knowledge and whether the equipment was properly maintained, the door was open or closed and latched, and what they were wearing. Let’s break it down by voltage class as well: 120/240; 480; 2300/4160; 13.8kv; above 15kv.

I’ll start –
13.8 KV - Electrician standing by equipment after cleaning was waiting for the unit to be energized. He was not the one who did the cleaning. Grounds were left on the switchgear and upon energization the blast blew off the door sending the electrican and the door toward a fence. Other than scrapes and bruises, the electrician was unharmed. He was wearing regular cotton work clothes.

2300V – Electrician was opening 2300V Starter for lockout. Motor was not running. While rotating switch an arc flash occurred. Severe 2nd degree burns to one arm requiring skin grafts. Door was secure and electrician was wearing cotton long sleeve work shirt and jeans. The equipment was properly maintained.

480V – Electricians installing bucket in energized MCC. Arc Flash occurred without injury. Door was open and feeder breaker tripped on fault. This was older equipment but was maintained.


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PostPosted: Wed Nov 04, 2009 8:41 am 
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Joined: Wed Sep 23, 2009 9:29 pm
Posts: 83
Location: Western Canada
Arc flash

I experienced an arc flash about 20 years ago when I was working on an energised 600 Volt emergency generator transfer switch. I was running a bare ground wire across the bottom of the controller and contacted a PT terminal. The flash was impressive - it came out about 3' and gave a me pretty good sunburn, a holey shirt, deafness for a couple of hours and a bright spot in my vision for a couple of days. The Main disconnect fuses blew limiting the damage to pride and evaporated transfer switch wiring. I got lucky - proper fusing worked even before the days of Arc Flash calculations.
Rules are different now, and I'm a little wiser (hopefully)...


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PostPosted: Thu Nov 05, 2009 5:38 pm 
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Joined: Thu Oct 18, 2007 7:10 pm
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Location: NW USA
This is a success story I've posted before on this forum:

Contract electrician was going to take phase rotation reading on a 480V padmount. Because we had done a study he suited up to Risk Level 4 and then in a momentary lapse, put the low voltage phase rotation meter on the energized 13.8kV terminals. There was a big ball of fire, that feeder shut down prematurely, everyone feared the worst, and the worker...........escaped unharmed. It is understood that is not a proper application of Arc Flash Protection but the thick suit worked admirably.

Other arc flash incident consists of a lineman pulling fuses on an overhead capacitor bank instead of using load break device. This drew an arc that went phase to phase, eventually tripping off the circuit. The lineman recieved a "sunburn" on his face.


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PostPosted: Fri Nov 06, 2009 10:46 am 
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Joined: Sun Aug 16, 2009 8:42 am
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Location: Lawrenceburg KY
20 years ago, 480v circuit, top side voltage testing on 60 amp fuse block. upstream fused protecton 800A fuse, using a "wiggy" (not mine) helping another guy. "Wiggy" leads had been replaced with old style simpson leads with long exposed metal points. The fuses were mounted behind large armature wires in an old enclosue. I was testing phase to ground when the large point test lead shorted between phases on the line side, (because of the angle I was having to hold the tester). The same personal injury as Canuck01 described. Looked like a raccoon with burnt hair. Cannot remember if the upstream fuses blew because I didn't do much the rest of the day. I ask a few years ago and no one remembers replacing them. Luckly my hand was on the wiggy about 8 inches from the arc so my hand was not burnt to bad. My face took the smoke and blast at around the 18 inch mark. When I calculated the IE a few years ago it was at 1.8 cal/cm2. A face shield would have been nice to have had on. I know what a 1-2 cal/cm2 flash looks like and feels like also. It wasn't my first but the worse. I was a cowboy electrician years ago. Like Canuko1 says hopefully wiser now. I would never use a wiggy afterwards. Later on I found many old horror stories of people using them.


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PostPosted: Sun Nov 08, 2009 12:32 pm 
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240 volt Arc Flash

30+ years ago, when I was still in college, I was moving my family into a rental for the summer and was trying to install the clothes washer and dryer.

After climbing over the back of the washer and dryer, wedging myself under the overhead cabinets and down into the hole behind the two devices, I realized that the pigtail that was attached to the dryer was not of the proper 3-terminal style of plug. A quick trip to the appliance store and back with the new pigtail, I climbed and wedged myself back in place and started to disassemble the old dryer pigtail.

As an after thought, and before I installed the wrong pigtail a second time, I raised the new pigtail up to the 240 volt outlet, meaning only to see if the two matched. Being wedged in so tightly, I had to shuffle myself a bit to see if they did indeed match, and in the process, accidently slipped the plug into the outlet. Luckily, the end of the pigtail was away from me but seeing as it was sitting unwired, all three conductors (grd and two hot leads) were shorted together, which caused a tremendous arc several feet in diameter that burned the hair off my arms, sunburned by arms, legs, and face, scorched black marks into the wall paint and dryer, made a very loud arc noise, and tripped the circuit off. I was looking the other way luckily and didn't damage my eyes. I did, however, jump up from my cramped position and slammed my head into the overhead cabinets hard enough to see stars.

After things calmed down a bit, I realized the power was off to our apartment. I found the 40 amp dryer circuit tripped as well as the 200 amp main. Resetting these still didn't bring power back on, so I went outside, where the neighbor in our 4-plex told me her power was off as well. After looking at the main power into the building, I found where it also tripped the 400 amp main to the 4-plex. Luckily it didn't take fuses out of the transformer as well.

While it is somewhat humorous looking back at my misfortune and poor work practices, several points can be made from my experience. To start with, don't assume that the time vs current characteristics of a 40 amp breaker backed up by a 200 amp main breaker will limit current to anywhere near their expected ratings. It would be interesting to duplicate this again under more controlled circumstances to determine if the smaller breakers couldn't break the arc which caused them to cascade up to the 400 amp main outside, or if the time/current characteristics of all three breakers were poorly matched, or possibly that the existing load that each of the breakers was carrying caused the cascading to take place.

Had the pigtail been sitting next to or beneath me, I very well could have been killed or at the least severly burned. The secondary affect of hitting my head on the cabinets was, however, what caused me the most pain and points to the importance of looking outside the box when setting up your arc flash boundries.

And last, it is important to note that this happened on a single phase 240 volt AC circuit. What I am also assuming is that what I experienced is properly defined as an "Arc Flash".


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PostPosted: Mon Nov 09, 2009 8:50 pm 
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Location: New England
Glad you survived.

What you experienced is not unusual for molded case breakers. They all had an instantaneous trip, and your arc draw enough current to activate them all. You're talking maybe 1 cycle to activate the trip and 2 to clear the arc. So they were all activated on the inrush and all tripped. This is not uncommon with small molded case breakers. In industry, we will often install a 'delta-wye' transformer when using 277 lighting to prevent a fault at a light ballast, from tripping the switchgear branch breaker.

The fuse on the pole didn't trip because the current on the primary was a lot lower and the fuse curve was slower.


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