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ekstra   ara
 Post subject: Data Collection
PostPosted: Tue Apr 10, 2018 5:31 pm 

Joined: Mon Feb 12, 2018 7:12 am
Posts: 3
I keep asking our PE this question but never seem to get a clear answer.
Question: When collecting data for an AF Study and we come to a 208v 3phase panel we stop there. But what if there is a 3 phase branch breaker that feeds a 3 phase disconnect. Do I still collect the info for this? The answer I get is “ from a one line diagram stand point, yes, gather the information. But we will not include this in the AF calculations.”
My thought is this disconnect will require maintenance so I think it should be included and get a label. I understand we are now under the 250v threshold. But there are still labeling requirements aren’t there? Some insight please!


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 Post subject: Re: Data Collection
PostPosted: Thu Apr 12, 2018 9:27 pm 
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Joined: Tue Oct 26, 2010 9:08 am
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Location: North Carolina
Let's be clear here. At or below 250 VAC the problem is that arcs are not stable like they are above that voltage. IEEE 1584 empirical method tests were only able to establish a stable arc once and the calculations below 480 VAC are based on a single data point. IEEE 1584 currently states that equipment fed by a single transformer rated 125 kVA or less at 208 VAC or less "need not be considered" (PPE not needed). IEEE C2 (NESC) goes about it a different way and gives a table of values of which the two entries from 250 VAC or less both require minimum PPE which under that standard is 4 cal/cm2.

Further, OSHA documented a case in 2009 in Georgia where one worker was hospitalized while the other died from temporary construction panel (240/120) thus proving that arc flash at these voltage levels is far more than a laboratory result. It's just that since arcs at these voltages and conditons are not stable enough to measure, much less make any kind of calculation that the best e can do is make some worst case assumptions and use a "table" based approach.

So it's not that you necessarily need to gather all the data but rather than it may not be necessary...the plan may be to attach a very generic sticker instead of one that is specific to that kind of equipment since it is so hard to get the data.


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