Clarifying 130.3 exception 1

I just got the 2009 version of NFPA70, I had been using the '04 edition. 130.3Exception 1 appears to exclude equipment meeting the listed criteria from "analysis."

Does this mean that:
1. There still may be a hazard but analysis isn't need, or
2. The hazard is so low that analysis isn't needed and arcflash PPE is unnecessary?

My understanding is that this means that these excluded equipment should not be able sustain an arc. This does not mean there is no hazard were there a fault.

Many people seem to be defaulting these areas to HRC 0. By doing even a cursury search of this site you can find a lot of debate over this approach. People with loads more experience than I don't necessarily feel that is the best approach.

It will have to be up to you and your facility to decide how you feel is the best way to approach this.

The IEEE paper said they were not able to sustain an arc below 240 volts. That's the reason its exempt. I typically recommend HRC1 as the minimum for all industrial work, but HRC0 is code acceptable. The code and Table is not perfect but sufficient for most cases.

Exceptions

The exception is being rewritten. It actually exempts some things like 208V systems which it was not intended to do. When we tested in IEEE 1584 we did see the 240V arcs with low fault current did self extinguish but you could still ignite clothing in some cases. I did a 240V meter base (single phase arc) two weeks ago at the lab and it held about 2 cycles every time but I wouldn't say it was no arc. We got about 5-10 cal/cm2 on the leather gloves holding the meter and about 1 cal/cm2 on the cotton t-shirt. If the shirt had been long sleeved it could have ignited. Being short sleeved the worker would have received some second degree burns and first on the face but we put on a faceshield. I agree with the above to wear a base of HRC 1-2 depending on most of your exposures.

NFPA-70E Tentative Interim Amendment

NFPA 70E®-2009
Standard for Electrical Safety in the Workplace®
TIA Log No.: 981
Reference: 130.3, Exception No. 1
Comment Closing Date: February 1, 2010
Submitter: Daleep Mohla, DCM Electrical Consulting Services, Inc.

1. Delete Exception No. 1 to Section 130.3, Arc Flash Hazard Analysis, which presently reads as follows:

Exception No. 1: An arc flash hazard analysis shall not be required where all of the following conditions exist:
(1) The circuit is rated 240 volts or less.
(2) The circuit is supplied by one transformer.
(3) The transformer supplying the circuit is rated less than 125 kVA.

2. Renumber Exception No. 2 as Exception.

(see attachment for full details)

This TIA was voted down. The exception is still in effect.

NFPA Code Alerts

I just signed up for NFPA code alerts for both 70 and 70E. Is this how you get notified of this stuff? I feel that I am kinda fishing in the dark; even though learning new stuff all the time.

I feel this issue is still not completely resolved and have therefore decided NOT to use the exception and go with EasyPower's option #1 concerning systems <250V so that we have accurate one-lines, matching labels and the ability to update easily when new calcs are released.

How should the following equipment be labeled for electrical hazards?

1. CB panels fed from a single 112.5kVA transformer at 208 volts.
2. The product of bolted fault current (5,320 A) and trip time (2.7 sec) is 14,364 Amp-sec.
3. SKM's PTW software calculated AF IE of 91 cal/cm^2 and a 252 inch (21 feet) Arc Flash Boundary. (I do not limit arcing time to 2 seconds.)

NFPA 70E (2009) 130.3 "Arc Flash Hazard Analysis":
Exception No. 1
An arc flash analysis is not required for 208 volt electrical devices feed from a single 112.5kVA transformer.
130.3 (A) (1) Arc Flash Protection Boundary for Voltage Levels Between 50 Volts and 600 Volts.
In those cases where detailed arc flash hazard analysis calculations are not performed for systems that are between 50 volts and 600 volts, the Arc Flash Protection Boundary shall be 4.0 ft, based on the product of clearing time of 2 cycles (0.033 sec) and the available bolted fault current of 50 kA or any combination not exceeding 100 kA cycles (1667 ampere seconds). When the product of clearing times and bolted fault current exceeds 100 kA cycles, the Arc Flash Protection Boundary shall be calculated.

Labeling for Arc Flash

Just left the NFPA 70E committee ROC meeting. This exemption looks like it is dying this time so all these devices will need to be calculated. They would need labels anyway if they are ever serviced per the NEC.

I understand the <125kVA exemption is currently 'under review', but for now how should these pieces be labeled? Should I run the software and apply a DANGEROUS 91 cal/cm^2 label?
Is the 1584 model correct at 208v?

What's being said about the 1584 model as applied 208V systems is that the arc doesn't maintain long enough to produce the incident energies predicted by the equations.

Since the 91 cal seems to be the result of an extended tripping time, it would appear that applying the 2 second cutoff would still be quite conservative in your case and allow this gear to be serviced.

If you aren't comfortable using the 125kVA exemption, perhaps the calculated IE with the 2 second cutoff is a good compromise. Calling the gear dangerous is probably extreme on one end of the spectrum, calling it Cat 0 may be extreme on the opposite end. If the 2 second cutoff puts you at 20-30 cal, this maybe a good compromise.

Ex Twidget
Thanks for your reply. I'm glad you see the nonsensical position this puts us in. It's either Cat 0, Dangerous or a compromise at Cat 3 (17cal/cm^2) using a 2 second cutoff.
I'll probably go with the Cat 3, but I won't feel good about it. We need a better tool.

I hope this exemption is not dropped without a replacement. As can be seen in this thread and many others, the calculated energy levels for 208 volt systems with low available short circuit currents can be unreasonably high based on the assumption the arc can be maintained for a lengthly period of time, which does not appear to be correct.

btw, NEC labels do not require any information about incident energy levels.

Well, I would that for the areas that would have qualified for the 130 Exception 1, that there would a definite time limit that can be used for calculations. This would reduce the hazard level.

There is a paper by Chet Davis of ESA (makers of EasyPower) that discusses using a time limit of 0.5 seconds for <250 V. There is a thread on this forum on that.