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 Post subject: Other NFPA/IEEE studies
PostPosted: Fri Oct 24, 2008 10:45 am 
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Location: St. Louis, MO
Given the video presented here:
http://www.arcflashforum.com/showthread.php?t=216

I would like to see the NFPA/IEEE study group perform some testing on long time arcing faults.

The current 1584 assumes time to be a linear component of the arc fault hazard. But looking at this video, the fault appears to last for nearly 4 seconds before extinguishing.
In the past, I have been in favor of the 2 second cut-off, but after seeing this video I may question it. My assumptions in favor of the 2 sec cut-off were that a number of things could happen:
1) The victim would be blown out of the area.
2) The material needed to continue the arc would vaporize and be blown out in this time.
3) If the material didn’t vaporize, the magnetic and pressure forces would be enough to separate the materials to such an extent that the arcing would extinguish.
Now, in the video, the victim does appear to have been blown clear of the cubicle, although it is hard to see because he is behind the door. But the arcing does continue for nearly 4 seconds.

However, even though the arcing continues, it seems to come and go in pulses. This would seem to imply, from strictly a measurement standpoint at a distance from the arc source, that the energy measured would is not instantaneous (or nearly so), and so may not result in the extreme calorie measurements that you would get from an application of the formulas, where time is a linear component.

So, what I am now wondering is this:
Is there a time value where the output of the event essentially levels off due to one or more of the things listed above occurring? If so, what is the maximum time that should be used? Is this value voltage dependent, as I suspect?


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PostPosted: Wed Oct 29, 2008 7:43 am 
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Location: Scottsdale, Arizona
I heard a rumor that this person was actually OK after the event. Hard to imagine but if you look close, he is standing off the side - a good distance between door hinge on his left and his feet to the right of the door.

The 2 second rule was based on reaction time assuming you would jump or be blown back and have room to do it. The caveat is you need room for the reaction which this person did not have. I thought it was "game over" for this person when I saw the video until someone pointed out where he was standing. The rumor(?) says he was back to work in a few days. If anyone else heard any info about this, it would be great to hear about it.

I have some new test data that I just received and will be posting soon (once I go through it all) about the duration of the arc. The data shows moderate faults clear sooner than lower faults in meter bases because they vaporize the electrodes faster. I'll sift through this data and create a new thread soon.

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PostPosted: Mon Feb 16, 2009 3:06 pm 
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Location: St. Louis, MO
For our estemed host:
So, what is the latest news from 1584? After the IEEE-IAS ESW in St. Louis, you should have plenty to fill us in on!

By the way, see you in April.


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PostPosted: Wed Feb 18, 2009 1:28 am 
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Quite a bit was discussed in St. Louis and we hope to have testing completed by next year (we'll see). My notes are not with me so I'll hold off with the details for now. I am in Europe (still here) for a few weeks with conferences and also a bit of work with a proposed European standard. I have about another week to go then I'll be back and provide a full update.

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