Take Your Pick

The 2012 Edition of NFPA 70E, the Standard for Electrical Safety in the Workplace, has made a significant change to the information requirements for arc flash warning labels.

According to Section 130.5(C), the following is now required:

“(1) Only one of the following:
     “a. Available incident energy
     “b. Minimum arc rating of clothing
“(2) Date of arc flash hazard analysis
“(3) Nominal system voltage
“(4) Arc flash boundary”

The last three items are straightforward. However, the first item has two possible options—incident energy or arc rating. Which is the better option? According to this section, either is acceptable, but one of the options may have a distinct advantage over the other.

Option A—Available incident energy
Listing the available incident energy on the label is a very common practice. Most arc flash calculation software automatically includes this value, based on the calculated incident energy at a specific piece of equipment, seemingly making option A the logical choice.

However, NFPA 130.5 requires the arc flash hazard analysis to be updated when a major modification or renovation takes place. The analysis also has to be reviewed periodically, not to exceed five years. This requirement emphasizes the importance of keeping the study up-to-date, so it accurately reflects current system conditions.

If a major change occurs, it could affect the calculated incident energy and result in the existing labels no longer containing accurate information. Subsequent updating of the labels could be both time consuming and expensive.

Option B—Minimum arc rating
Rather than using the available incident energy, option B may be the better approach. Listing the minimum arc rating could reduce the need to relabel equipment when the study is updated.

For example, say Acme Widget Co. completed its arc flash study two years ago. The company’s main distribution panel (MDP) has a calculated incident energy of 5.8 calories per square centimeter (cal/cm2). This is the value listed on the existing arc flash warning label.

Based on the incident energy being below 8 cal/cm2 at most locations, Acme has standardized the arc rating of its protective clothing to 8 cal/cm2. This rating is sufficient for all but a few locations where workers have to use a higher rating.

Acme just completed a major change to its incoming service, and according to NFPA 70E requirements, the company reviewed and updated its study. The new calculations indicate the incident energy at the MDP increased from 5.8 to 6.7 cal/cm2. Although the 8 cal/cm2 personal protective equipment is sufficient for 6.7 cal/cm2, the existing label is still marked with 5.8 cal/cm2 and is no longer correct.

If Acme had listed its minimum arc rating of 8 cal/cm2 at this location instead, the label would still be correct regardless of whether it had 5.8 or 6.7 cal/cm2.

Arc flash boundary?
If the incident energy changes, the arc flash boundary will also change, since the two are related. Does this mean the label also needs to have this value updated? Not necessarily.

In “The Big Bang: Arc Flash Hazards” (Electrical Contractor, November 2009), I discussed how to develop a standardized arc flash boundary to simplify the process. To determine a standardized boundary, review all of the calculated arc flash boundaries, select the largest one within reason, round it up, and adopt it for a particular system or voltage level. A standardized boundary may require a few exceptions, but overall, it allows a much simpler approach with a uniform distance.

If Acme used this method, the information on the label would also still be correct as long as its new arc flash boundary remains less than its standardized boundary.

And the date?
The date is now required on the label. When a study is revised or reviewed, a small tag could be added to the existing label to verify that it is still adequate. This is similar to tags placed on equipment after it has been tested.

Short-circuit study analogy
A short-circuit study will determine if equipment has an adequate interrupting or withstand rating. Short-circuit calculations are compared to the rating to verify it is adequate.

A similar approach can be used for arc flash warning labels. List the minimum arc rating on the label, and use the calculated incident energy to verify the arc rating is sufficient.

KISS strikes again!
The revision to the labeling requirements in the 2012 edition of NFPA 70E greatly improves the labels’ usefulness for the end-user. However, like most things in life, keeping it simple is also an important part of the process.

PHILLIPS, founder of www.brainfiller.com and www.ArcFlashForum.com, is an internationally known educator on electrical power systems and author of “Complete Guide to Arc Flash Hazard Calculation Studies.” His experience includes industrial, commercial and utility systems, and he is a member of the IEEE 1584 Arc Flash Working Group. Reach him at jphillips@brainfiller.com.

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