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 Post subject: 2012 NFPA 70E Doors Open / Doors Closed
PostPosted: Thu Jun 02, 2011 6:05 am 
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Continuing the doors open / doors closed discussion:

Just thought I would throw this one out there and then run :cool:

In the 2012 Edition of NFPA 70E, the Arc Flash Boundaries (AFB) and maximum clearing times and short circuit currents are now listed for each task in table 130.8(C)(15)(1) i.e. the HRC Tables with a new number.

For a few of the tasks the AFB is 0 inches with the doors closed and 235 inches with the doors open - the maximum short circuit current in each case is 35 kA and the maximum clearing time is 0.5 seconds.

Credit for the doors? Interesting….

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PostPosted: Thu Jun 02, 2011 3:04 pm 
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brainfiller wrote:
For a few of the tasks the AFB is 0 inches with the doors closed and 235 inches with the doors open - the maximum short circuit current in each case is 35 kA and the maximum clearing time is 0.5 seconds.

Credit for the doors? Interesting….


It sure seems like there is credit for the doors to me. Both cases have the same upper limit for short circuit current and clearing time which should mean the same incident energy.

If I had these values for a calculation study, I would be posting the same arc flash protection boundary whether the doors were open or closed for the person performing work while an arc flash hazard existed.


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PostPosted: Thu Jun 02, 2011 6:12 pm 
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brainfiller wrote:
Continuing the doors open / doors closed discussion:

Just thought I would throw this one out there and then run :cool:


Yeah, you better run :D


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PostPosted: Fri Jun 03, 2011 5:46 am 
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Doors do make a difference no matter what some may think; I’ve seen this first hand more than once. There are even a few test videos out there showing the differences. The problem is no one has come up with a multiplying factor to adjust the calculations or to assist with some type of risk assessment. Everyone continues to treat a fully exposed and a doors or panels closed configuration as the same with regards to “heat exposure”; this has never made sense to me. I agree doors can fly open or projectiles can hit the worker but we’re not calculating impact hazard.


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PostPosted: Fri Jun 03, 2011 6:30 am 
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I think the problem here is that the rules were written that way because the condition of the doors, missing bolts, bolts not tightened, etc., is unknown and as a result a conservative measure was recommended. More times then not I have found these conditions on customer's equipment. Also, when the doors do open during an arc fault, the heat, may be somewhat less, but at what value do you use for the calculations. It all depends on how long they stay closed.


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PostPosted: Fri Jun 03, 2011 7:19 am 
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richxtlc wrote:
I think the problem here is that the rules were written that way because the condition of the doors, missing bolts, bolts not tightened, etc., is unknown and as a result a conservative measure was recommended. More times then not I have found these conditions on customer's equipment. Also, when the doors do open during an arc fault, the heat, may be somewhat less, but at what value do you use for the calculations. It all depends on how long they stay closed.


Right, too many variables (You forgot vents).


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PostPosted: Fri Jun 03, 2011 7:39 am 
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Zog wrote:
Yeah, you better run :D


Guess I can run but I can't hide. :cool:

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PostPosted: Fri Jun 03, 2011 10:10 am 
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Zog wrote:
Right, too many variables (You forgot vents).


You're right, but sometimes I don't like to vent.


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PostPosted: Sat Jun 04, 2011 3:58 pm 
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richxtlc wrote:
I think the problem here is that the rules were written that way because the condition of the doors, missing bolts, bolts not tightened, etc., is unknown and as a result a conservative measure was recommended. More times then not I have found these conditions on customer's equipment. Also, when the doors do open during an arc fault, the heat, may be somewhat less, but at what value do you use for the calculations. It all depends on how long they stay closed.


This is a very good point.
In order to determine a proper analysis I believe you would want to calculate as though the doors were open. It is too easy to overlook the condition of the doors at the time of calculation or more importantly at some future date.

Equipment does change and not always for the better.

[url="http://www.coverallsale.com"]www.coverallsale.com[/url]


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PostPosted: Wed Aug 24, 2011 2:46 pm 
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I heard in a training class a while ago that doors can be traveling around 600 mph when they are blown off. That'll leave a mark!


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