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 Post subject: NESC 2012 Table 410-1
PostPosted: Tue Sep 06, 2011 1:07 pm 

Joined: Thu Mar 13, 2008 4:23 am
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Location: Canton, OH
Has anyone picked up or seen the 2012 NESC? I am currently placing an order for this and the Handbook.

I was curious if "proposed table" 410-1 made it into the 2012 code. This table was supposed to clarify work on secondary systems <1000V.

If it did make it into the code, will any utilities change their current practices for work involving hazards <1000V? Using the calculations methods of IEEE 1584 I have calculated energy levels much higher than what is listed in the table (ecspecially for 480V, pad mounted transformers). I see this table as being at best, a bare minimum for energized work.

Any thoughts?


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PostPosted: Tue Sep 06, 2011 4:52 pm 
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GPD_Steve wrote:
Has anyone picked up or seen the 2012 NESC? I am currently placing an order for this and the Handbook.

I was curious if "proposed table" 410-1 made it into the 2012 code. This table was supposed to clarify work on secondary systems <1000V.


It's in there. It includes self contained meters, pad mounted transformers, a whole list of equipment. ...and 14 footnotes :)

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PostPosted: Wed Sep 14, 2011 10:20 am 
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It changed a bit from the proposed version.


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PostPosted: Tue Oct 25, 2011 12:11 pm 

Joined: Wed Jun 24, 2009 4:45 pm
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GPD_Steve wrote:
Using the calculations methods of IEEE 1584 I have calculated energy levels much higher than what is listed in the table (ecspecially for 480V, pad mounted transformers). I see this table as being at best, a bare minimum for energized work.


Just got my hands on the 2012 NESC. I agree with your comments about 480V pad-mounted transformers having much higher energy levels when using IEEE 1584. This table is quite a change from the 20 cal per cm2 in the proposed table.

Footnote 9 indicates the following,
"Industry testing on 480 V equipment indicates exposures on pad-mounted transformers do not exceed 4 cal/cm2. (See Eblen and Short [B31].)"

I guess I need to read the referenced Eblen and Short article (Arc Flash Testing of Typical 480V Utility Equipment) to understand how they came to this conclusion.

I suspect there is enough differences in the IEEE 1584 test enclosures physical layout and spacings compared to typical utility pad-mounted transformer cabinets to make the IEEE 1584 calculations not applicable.


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PostPosted: Wed Oct 26, 2011 4:48 pm 
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From the Pre-print proposals:

[INDENT]The WG’s initial evaluations concluded that aside from anecdotal evidence no technically substantiated data based upon specific industry testing existed to justify the creation of a new table, similar to existing Tables 410-1 and 10-2, for voltages less than 1000 V. However, during the spring and summer of 2008, the Pacific Gas and Electric Company initiated and completed a series of scientific tests to determine the arc flash characteristics of 480 V self-contained metering equipment by creating fault conditions at various kA levels (sans fault protection devices).

Based on PG&E’s test results (which are included with this CP) and the application of an accepted industry standard (IEEE Std 1584-2002), the WG submitted a report to Subcommittee 8 that included revisions to Rule 410A3 and a new Table (410-1).[/INDENT]

My understanding is that PG&E found these faults to be self clearing. Note the parenthetical regarding fault protection cevices.


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PostPosted: Wed Feb 01, 2012 3:08 pm 

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Consider 480V padmount feeding secondary thru a pull box to a self contained meter. Am I missing something or does this say a worker needs 4cal the the transformer lugs, 8cal in the pullbox, and 20cal at the meter? Seems backwards.


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