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 Post subject: Tables ?
PostPosted: Wed Oct 06, 2010 4:38 pm 
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Joined: Sat May 01, 2010 2:20 am
Posts: 36
I am told that if a electrical service is out of parameters to do a arc flash study that you can not use the tables at all. If this is the case does this mean you can not use the tables in any of the mcc throughout the plant because the switchgear at the service is out of the paramaters to do the study? Or is it possible that the tables can be used for the other mcc's in the plant ?


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PostPosted: Wed Jan 05, 2011 5:47 pm 
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Joined: Mon Dec 06, 2010 11:33 am
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Location: LUBBOCK TX
Nfpa 70e t130.7(c)(9)

The best suggestion I have, is obtain a copy (of your very own) of NFPA70E-2009.
The Section clearly states the tables are for specific conditions, and includes all the notes. 130.3 allows the table as an alternative to conducting an AFHA, if the table is not applicable, then the AFHA must be performed.


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PostPosted: Wed Jan 05, 2011 8:09 pm 
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Joined: Mon Jan 18, 2010 11:35 am
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Location: Wisconsin
toolbbin wrote:
... is it possible that the tables can be used for the other mcc's in the plant ?


Yes, it is possible.


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PostPosted: Thu Jan 06, 2011 9:02 am 
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Joined: Tue Oct 26, 2010 5:00 pm
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Location: Maple Valley, WA.
Determining the energy level at various locations is a difficult task if you are not familiar with calculating short circuit currents or looking at device time current curves.

The Task Tables in NFPA 70E have a limited use. They are better than nothing but can easily be misapplied. In some areas of your plant, you may find that the available fault current exceeds the table foot notes (limit of short circuit current). In other locations, you may find that the device operating time exceeds notes at the end of the table. You also may find that there are locations where both the fault current and the interrupting time exceeds the table notes.

For areas where the Task Table cannot be used, then you must use the equations in IEEE-1584 or NFPA-70E.

_________________
Robert Fuhr, P.E.; P.Eng.
PowerStudies


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