I just returned from the IEEE 1584 Committee Meeting held in Toronto, Canada on September 17, 2011. Here are a few highlights.

Update of IEEE/NFPA Arc Flash Collaborative Research
Testing for the development of new arc flash equations began December 2008.

Time Line of Future Developments:
Assuming all testing is completed by December 2011, it is anticipated that new calculation models will be completed by September 2012. After that, the IEEE 1584 committee will begin working on including the equations into the 1584 new standard.

A graph was shown at the meeting which plots the test results against calculated results. There was only a maximum absolute error of 3.7% and 1.37% mean absolute error. i.e. much more accurate.

Sound levels are being studied and here are a few test results - Bolted faults above 5 kA can produce sound pressure of 140 dB 2 to 3 meters away. The maximum sound pressure was 170 dB. Keep in mind every 3dB increase is actually doubling the sound pressure. This is not too surprising since my experience with testing low current low voltage sounds like a shot gun going off. Luminance and pressure are also being studied as part of this research.

125 kVA Transformer Exception

I mentioned previously in the forum about proposed language for a new low short circuit current, low voltage exception that I submitted. A few other options were also submitted using different approaches. A lengthy discussion regarding proposals led to a few conclusions.

1. It was almost unanimous that we still need an exception for a low s.c. current, low voltage cut off for calculations.
2. Out of three options that were discussed, the option using a low cut off for short circuit current and voltage was most popular. Other options were also discussed.
3. More analysis is required to define what the current and voltage levels should be. More work to be done on this.

IEEE 1584.1 Guide for the specification of Scope and Deliverable Requirements for an Arc-Flash Hazard Calculation Study in Accordance with IEEE 1584.This is the proposed standard that I Co-Authored. This proposed standard went out for voting and had 102 balloters. There were 278 comments which have been mostly resolved. This standard is getting closer to the finish line and hopefully will help guide people with what should be the minimum requirements of an arc flash hazard calculation study.

I hope this helps keep everyone in the loop with what is going on “behind the scenes”. By the way, anyone can sit in on these meetings. The occur at IEEE’s Electrical Safety Workshop and the PCIC conference every year.

IEEE 1584 400 HZ Arc Flash Calculations

Are there any plans for IEEE 1584 to test Arc Flash in 400 HZ systems in the future. We have 575-2400V-120/200V, (3) 400 Kva total of 1200 KVA connected in parallel 400 Hz distribution transformers/switchgears.

Not that I know of. 400 Hz is not on the radar screen. It is 60 Hz up through 15 kV with better equations and ultimatly "official" DC equations will be included.

re: 125kva exception

Are we supposed to relabel 240V (and below) panels now per NFPA70E 2012 that eliminates the exception and then perhaps relabel in a year if there is another exception?

Where this exception was located in NFPA 70E it now refers to IEEE 1584 for guidance which still has the exception. I am attempting to develop a clearer version of the exception using perhaps a low end current but that will be sometime in the future i.e. at least a year or two. Like in the past, I'll keep everybody updated on any progress here on the forum.

Labeling the "exception"

Thanks for the update Jim. Until then, looking for some guidance on how to label the equipment that is presently fed from a transformer 125kVA or less and less than 240V. I do know the PTW software has an option to make a category 0 by default, but the task tables identify removing the covers of panelboards as a category 1 task. I know the task tables in NFPA are done with certain assumptions, but as engineers wouldn't we want to take a more conservative approach? That being said would a category #1 with a 19inch boundary be most appropriate? Or am I mixing apples and oranges here? Your help is greatly appreciated.

Thanks!

JCV, The usual problem is that smaller transformers limit the short circuit current where the transformer’s primary protective device may take too long to operate and clear the fault. The primary is typically used due to a concern that the arc flash could escalate ahead of the secondary panel’s main.

The longer clearing time is what leads to a higher “calculated” incident energy. A lot of the testing and debating revolves around the question: Can a low current / low voltage arc sustain until the primary device trips or will it end in a few cycles on its own.

There are a few special cases where the arc can sustain long enough to be a problem but not in most cases. So for now, the conservative approach with calculations is to either use the primary device’s clearing time (even if it is long) or cut the time off at 2 seconds if appropriate. The HRC tables do indicate lower categories but keep in mind there are limits of fault current and duration and the duration is often the problem.