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 Post subject: General Notes from Table 130.7C9
PostPosted: Mon Apr 27, 2009 6:09 pm 
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Location: New England
General notes from Table 130.7C9 states:

(d). For systems rated less than 1000 volts, the fault currents and upstream protective device clearing times are based on an 18 in. working distance.

(e) For systems rated 1KV and greater, the Hazard/Risk Categories are based on a 36 in working distance.

Why do you think NFPA uses 1000V as the transition voltage. Most industry jargon would take anything 600V and under as 'low voltage' and 601V and higher as 'medium voltage'. Is it a Monk thing, they just like round numbers.

Also, why not follow the accepted norms of 24" for working low voltage switchgear?

Further, note (f) ..."For equipment protected by upstream current limiting fuses with arcing fault current in their current limiting range (1/2 cycle fault clearing time or less), the hazard/risk category required may be reduced by one number.

Does this mean that if the Table HRC is 0, that we are re-introducing the PPE Level (-1)?


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PostPosted: Fri May 01, 2009 9:57 am 
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Location: Scottsdale, Arizona
Haze,

You have to quit reading 70E so closely, your finding all the hidden problems! :eek:

Actually what you pointed out does appear to be more inconsistencies. Category -1 was suppose to have been eliminated but this footnote does seem to lead you back into it.

I think the 18 inch and 36 inch distances are from IEEE except they did not get it completely correct. IEEE uses a different working distance for LV switchgear than panels and MCC's, and NFPA seem to have lumped it all as the 18 inch panel working distance.

More Revisions!

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