Arc Flash and DC Systems

[HenryOhm]

thread238-218868

I was reading through thread238-218868 that discussed Arc Flash and Battery Strings.

Some statements seemed to be made that there are no recognized standards for DC arc flash. I think what was meant was arc flash calculations but want to be sure.

In NFPA 70e (2009), Section 320 (intro), Batteries and Battery Rooms, it says, "Working with batteries exposes a worker to both shock and arc flash." But, I can't see that any of the rest of 320 discusses arc flash. Section 310.5(C) for Electrolytic Cells interestingly excludes Section 130.3.

But for either case, wouldn't section 130.7, specifically Table 130.7(C)(9), still be in effect, ie the Table approach to required PPE? Neither the voltages in the table or the kA short circuit current in Notes 1-4 are specifically called out as "VAC" or "kAAC"

I also see no AC limitations to any of the scoping parts of the standard such as Section 90.2, Scope.

Would it then be correct to say that NFPA 70e (and OSHA 29 CFR Part 1910) do cover DC but it is simply IEEE1584 that does not?

Thanks so much for any help.

 

[alehman]

The arc clearing behavior of overcurrent protective devices is vastly different with DC than AC. The tables and formulas in NFPA 70E are largely empirical and have not been validated for DC and I would not expect them to be the same. The HRC values in 130.7(C)(9) would not apply for DC.

The PPE insulating requirements may come closer to being valid, but still have not been tested for DC.


Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[racobb]

But I think that 70E applies to greater than 50 vdc. Am I wrong or are we agreeing that very little dc data exists?

Alan

 

[alehman]

Portions of 70E definitely cover DC, but the sections on arc flash hazard (130.3 & appendix D) do not apply. Although I don't see any explicit exclusions for DC, those sections are clearly based on AC calculations and use terms such as cycles, 3-phase and MVA throughout.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[alehman]

I think the intent of 70E is to provide adequate safety measures. That applies regardless. It's just the analysis methods that don't work for DC.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[Zogzog]

The 70E applies to DC just as well as AC. There just are not any specific DC arc flash calcs, yet, IEEE has doen the needed testing and is working on the calculations.

Good references in this thread, the host of this is part of the IEEE team doing the research.

http://www.arcflashforum.com/showthread.php?t=448

 

[HughHoagland]

The 2012 NFPA 70E standard will have much more information on DC. I'm a member of IEEE 1584 and NFPA 70E's DC Taskforce. Monday they voted to include a new table guide and assistance in Annex D. This info will be published in the ROP document available by 6/25/2010 from nfpa.org.

I have attached the exact site below.

Hugh Hoagland

http://www.e-hazard.com

http://www.arcwear.com