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 Post subject: NESC Table 410-1 Calculations
PostPosted: Thu Mar 06, 2008 11:55 am 

Joined: Wed Mar 05, 2008 7:42 am
Posts: 16
Hi,

After some reading of comments in the forum, it seems clear that NESC Tables 410-1 was build based on Arc Pro software or some equations close to what the software is offering.

Does someone knows what standard Arc Pro software is using? Does someone knows what equations or standard there are using.

I've compared Heat Flux equations, IEEE-1584 and NFPA-70 E. The Heat Flux seem to be the best candidate, but it is still far from NESC Tables.

I'm looking for the equations to obtain results from NESC tables.

Thanks!

Electric John


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PostPosted: Wed Jun 04, 2008 11:22 am 
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Joined: Wed Jun 04, 2008 9:17 am
Posts: 428
Location: Spartanburg, South Carolina
You've gotten no responses, so I'll bump this in the hopes of getting one. I don't have an answer, but I don't feel comfortable using software when I don't know the theoretical basis for it.

Other posts indicate that Arc Pro matches the NESC tables, but what about situations not covered by the tables? Does Arc Pro cover three phase arcs?

NESC requires an assessment of potential exposure. It does not say only exposures to single phase arcs, but the tables do not cover three phase arcs. The IEEE-1584 Ralph Lee method covers three phase arcs, but is very conservative for voltages above 1 kV.

Jim


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PostPosted: Fri Jun 06, 2008 7:56 am 
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Joined: Mon Sep 17, 2007 5:00 pm
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Location: Scottsdale, Arizona
Both the Duke heat flux and Kinectrics program's formulas are two of the mysteries of the universe. I know several people that have attempted to obtain the formulas from the Kinectrics model and they are unavailable. I am not sure why. This means we have to take the results for what they are and hope they got it right.

Yes, my understanding is the NESC tables are based on Kinectrics program, I know the person that put the table together. It is the best that there is in the absense of any recent research. The Electric Power Research Institute (EPRI) is going to undertake more advanced research for the utility arc flash calculations involving scenarios such as overhead T and D single phase arc flash events. I am sure like may projects, this will take a long time. I will likely receive an occasional update at the IEEE 1584 meetings and I will post any progress here on the forum.

This seems to be the classic "cart before the horse" in that the NESC is mandating an arc flash assesment by January 1, 2009 without very good methods to achieve it for overhead T and D. Equipment such as switchgear etc. can be modeled using one of the many commercially available programs that use the IEEE three phase models.

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PostPosted: Fri Jun 20, 2008 6:40 am 

Joined: Wed Dec 12, 2007 6:54 am
Posts: 9
Steve Cress (Kinetrics) one of the co-authors of Arc Pro gave a presentation at the EPRI workshop in Chicago on 4/24/08.

The methodology used in Arc Pro to calculate the heat energy is finite element analysis, it is not a simple equation.

Validation was performed by carrying out tests with the prescribed parameters.


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PostPosted: Thu Aug 14, 2008 7:12 pm 

Joined: Thu Aug 14, 2008 5:00 pm
Posts: 10
Location: Wisconsin
Arcpro matches the NESC tables in my experience. As the table states and Arcpro also states the equations are based on single-phase open-air arcs. Arcpro gives you the range of multipliers if you have multi-phase or arc in-a-box scenarios which can be up to 6.5 times the Arcpro calculated result since Arcpro works for single-phase open-air arcs.


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