ECN Forum Forums Code Related Discussion NEC & other Code issues NFPA 70E Annex D Out of Range SCA

NFPA 70E Annex D has calculations D.6.1 and D.6.2 that need a value for F (short-circuit current, kA) to do the calculation. The value has a qualification statement that says (for the range of 16kA to 50 kA). What do we do for values outside of this range, especially for values below the 16kA?

I must not have the latest standard, since I don't find annexs in my copy (NFPA70E-2000), but I did find the formula you mentioned, along with a statement that theseequations were derived in the IEEE paper by R.L. Doughty, T.E. Neal, and H.L. Floyd, II, "Predicting Incident Energy to Better Manage teh Electric Arc Hazard on 600V Power Distribution Systems", Record of Conference Papers IEEE IAS 45th Annual Petroleum and Chemical Industry Conference, September 28-30, 1998.

Perhaps you could find a copy of this to see if they adress the out of bounds amounts you refer to.

Rick Miell

The range statement is found in NFPA 70E 2004.

NFPA 70E calculation methods have a range of 16 kA - 50 kA. The IEEE 1584 method has a range of 0.7 kA - 106 kA. Generally, when outside of these ranges use Lee's equations.

 
Aside — Some might think that the 70E/1584 arc-flash interest is purely 21st-century, but early impetus for this work is a 1982 IEEE paper by electrical engineer Ralph H Lee at www.ieee-pcic.org/archive/The%20oth...20%20Electric%20Arc%20Flash%20Burns.pdf.

He is not to be confused with Dr Raphael C Lee of the Electrical Trauma Research Program at the University of Chicago, http://etrp.bsd.uchicago.edu/areas/overview.html who has been a very notable pioneer in his own right for emergency and long-term severe electrical-burn treatment.

Bjarney,
Thanks for the backup, I didn't explain.