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 Post subject: AFB over 600 V and NFPA tables
PostPosted: Wed Mar 18, 2009 7:12 am 
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Hello,

How to know the AFB with voltage levels over 600 V when using the NFPA tables? 130.3(A)(2) says it's the distance where IE is 1.2 cal/cm^2, but there's no default value like the 4.0 ft with voltage between 50 V and 600 V.


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PostPosted: Wed Mar 18, 2009 7:36 am 
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Vincent B. wrote:
Hello,

How to know the AFB with voltage levels over 600 V when using the NFPA tables? 130.3(A)(2) says it's the distance where IE is 1.2 cal/cm^2, but there's no default value like the 4.0 ft with voltage between 50 V and 600 V.


Needs to be calulated, and in most cases the 4 foot rule dosent work for 480V either.


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PostPosted: Wed Mar 18, 2009 7:41 am 
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In NFPA 70E-2009, Article 130.3 (A) (2) for AFHB for voltage levels greater than 600V contains a FPN that states for information on estimating the Arc Flash Protection Boundary, see Annex D.

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PostPosted: Wed Mar 18, 2009 7:42 am 
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Zog wrote:
Needs to be calulated, and in most cases the 4 foot rule dosent work for 480V either.


Then what's the point of the tables for gear over 600V? To calculate the AFB, I need pretty much the same values than to calculate the IE, so I don't see an advantage in using the tables.


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PostPosted: Wed Mar 18, 2009 8:30 am 
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Vincent B. wrote:
Then what's the point of the tables for gear over 600V? To calculate the AFB, I need pretty much the same values than to calculate the IE, so I don't see an advantage in using the tables.


Correct, you need to ensure you need the note (Limitations) of the tables in order to use them, by the time you do that you are halfway to finishing your arc flash study.


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