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Have you ever had an arc flash occur on its own without a person involved?
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 Post subject: Arc Flash Without a Person Involved?
PostPosted: Sun Sep 04, 2011 3:06 pm 
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Joined: Mon Sep 17, 2007 5:00 pm
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Location: Scottsdale, Arizona
This week's question is based on a few recurring forum discussions.

Have you (or someone you know/work with) ever had an arc flash occur on its own without a person being involved? Stories are always welcome!
  • Yes
  • No

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Jim Phillips, P.E.
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PostPosted: Mon Sep 05, 2011 1:18 pm 

Joined: Tue Jul 24, 2007 5:00 pm
Posts: 11
Location: Chicago, IL
Are you sure you want to ask this question?

In 2004 the arc flash hazard involved exposed conductors.

In 2009 it expanded to include "interaction" even if the doors are closed.

I can see this question leading to "It can happen anytime, anywhere, without warning" leading to even more restrictions. :eek:


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PostPosted: Mon Sep 05, 2011 1:51 pm 

Joined: Mon Jan 31, 2011 6:28 am
Posts: 14
The only real-life (ie. non-video) arc flash incidents I've seen have not involved people. The first one was a QMB style Power Panel tapped off of an open-wire feeder. 3" conduit was run from the panel to the feeder, to protect the conductors, but rain came in from a leaky roof/windows and ran down the conductors and caused an arc on the primary side of the QMB's main fuses. Because of the nature of the feeder, this particular panel was located about 1000' away from the switchgear/fuses, a bystander had enough time to video tape the incident with his cell phone. I heard, after the fact, that an engineer cleared the fault by going to the substation and operating the disconnect :eek: ! Apparently only a single fuse blew. Only one phase of a three phase 480V system. Nobody was injured, as it was a fairly remote panel.
The second one happened 20' away from me (with me walking away from the panel) on the DC side of a rectifier that feeds a 90,000 ADC bus. Humidity caused the 125VDC control wires for the blown fuse indicators to droop and caused an arc across the diodes. It sounded like a bomb, and I could feel the pressure wave on my back from 20' away. I wasn't facing it, but I could see the flash in my peripheral vision as if lightning had struck behind me! It was an instantaneous trip, as every DC overcurrent relay on the line tripped. Scary stuff, but I still maintain that there is a low risk of exposure for someone simply walking past a panel. The odds were in my favour...


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PostPosted: Mon Sep 05, 2011 2:43 pm 
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Joined: Sun Dec 23, 2007 1:44 pm
Posts: 348
Location: Charlotte, NC
Do squirrels count, or would that still qualify as interaction......albeit by non-humans?


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PostPosted: Mon Sep 05, 2011 2:45 pm 

Joined: Tue Jul 24, 2007 5:00 pm
Posts: 11
Location: Chicago, IL
m_cmbl wrote:
...but I still maintain that there is a low risk of exposure for someone simply walking past a panel. The odds were in my favour...


I agree - low risk, but I get the feeling that does not always enter into all of this.


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PostPosted: Mon Sep 05, 2011 9:11 pm 
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Joined: Mon Mar 29, 2010 5:02 am
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Had to fix 2 good ones of them...
One was a phase to phase failure on the line side of a main breakeron a 480 volt 1200 Amp service.. It blew a 2" hole through the front of the door of the cubicle, and took out power to an industrial park.. Later on, when we asked them who did their electrical switchgear maintenance they said "whoever's sticker was on the front of the cabinet." When we let them know that the Utility Company who's sticker was on the cell had changed names about 3 times and didn't offer Low Voltage maintenace past their meter, their faces became rather long..

The other was an underground 4,160 volt cable that failed with no load on it, and none being applied. The short blew the doors open to the termination cabinet on the 5 MVA transformer. There was signs of molten copper up the cables and inside the transformer. When I under took the repairs, I believe we found the design and construction flaw. They had installed a 4" PVC conduit from the transformer to a cable tray to take the teck cable into the building. The top of the conduit was not properly sealed, and we speculated that over time water had leaked in and over the winters had expanded and contracted enough to damage the cable. It was found that the conduit was installed for "mechanical protection". Had they installed a sleeve into the tray, there wouldn't have been the chance of cable damage.


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PostPosted: Tue Sep 06, 2011 2:33 pm 

Joined: Wed Aug 31, 2011 3:33 pm
Posts: 14
Location: Denver, CO
squirrels - that is hilarious


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PostPosted: Wed Sep 07, 2011 4:27 am 
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Joined: Mon Mar 29, 2010 11:52 am
Posts: 110
Location: Yankton SD/ Lead SD
JCV wrote:
squirrels - that is hilarious


Probably not for the squirrels.


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PostPosted: Wed Sep 07, 2011 6:53 am 
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Joined: Tue Feb 24, 2009 7:05 am
Posts: 252
You can see [url="http://www.arcflashforum.com/showthread.php?t=742"]here[/url] the result on a cat and rat.

Imagine you touching the busbar now, or even being near when the cat gets zapped...


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PostPosted: Wed Sep 07, 2011 10:57 am 
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Joined: Wed Jun 04, 2008 9:17 am
Posts: 428
Location: Spartanburg, South Carolina
cbauer wrote:
Probably not for the squirrels.

This squirrel got into 12 kV without proper PPE.
Image


Attachments:
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non standard working distance.jpg [ 196.68 KiB | Viewed 2006 times ]
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PostPosted: Wed Sep 07, 2011 1:15 pm 

Joined: Tue Nov 09, 2010 5:00 pm
Posts: 19
Location: Virginia
jghrist wrote:
This squirrel got into 12 kV without proper PPE.
Image


Tough day at the office? :)


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PostPosted: Tue Sep 20, 2011 7:19 am 

Joined: Tue Sep 20, 2011 6:49 am
Posts: 5
Location: Earth
Poor squirrels.

We had an incident where I believe (the event happened before I started doing Arc Flash) a 4000A switch gear arc'ed on it's own over the weekend when loads weren't especially high.

However, one person showed me pictures of water dripping from the ceiling near the switchgear. So I imagine that it was the water that caused the fault and the electrician blamed it on the devil. And since that argument doesn't have a lot of technical papers behind it, he blamed it on arc flash.


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PostPosted: Sun Sep 25, 2011 8:10 am 
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Joined: Sat Feb 27, 2010 5:59 pm
Posts: 71
Location: Cincinnati, OH
We have had 40 year old 4160 x 120V control power transformers fail several times. One failed a few years ago when some electricians were at the far end of the substation, not doing anything with the motor control center or any other associated equipment.


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