Electrical safety

Responding is Hugh Hoagland, senior partner and co-founder, and Zarheer Jooma, electrical engineer and partner, e-Hazard, Louisville, KY.

In December 2018, a revision in IEEE 1584-2018 – IEEE Guide for Performing Arc-Flash Hazard Calculations changed calculations substantially on some equipment. The 2002 edition of the standard excluded equipment less than 240 volts supplied by a single transformer rated less than 125 kilovolt-ampere. The 2018 standard, however, was backed by research showing that because “sustainable arcs are possible” at these levels, they need engineering calculations in many cases.

There is no easy rule for these common “208V” systems. In the research, these could be worse than the 2002 edition indicated. At one site, all 208V equipment fed from 45kVA transformers produced incident energies greater than 1.2 cal/cm², while 75kVA transformers produced less than 1.2 cal/cm². In another plant, 30kVA transformers produced greater than 1.2 cal/cm² in one area and less than 1.2 cal/cm² in another part of the plant. Time and arcing currents are a weird and wonderful phenomenon in arc flash hazard analysis, making it impossible to use a transformer nameplate or a breaker rating for rough estimates. The 1.2 cal/cm² number is most important because this is the level at which NFPA 70E requires arc flash personal protective equipment and does not allow common workwear.

It must be noted that building owners are as responsible as the equipment user/employer under NFPA 70E, so both entities must assess the risk.

Can you wait for the five-year recommended review cycle as required in NFPA 70E?

The standard says to update the study if: A) changes in the electrical system can influence the results, or B) at intervals not to exceed five years. Although the standard does not mention changes to the engineering standard for calculation, the new NFPA 70E does list it as the only updated standard method and the one common in engineering software. Additionally, the OSHA General Duty Clause and NFPA 70E-2021 110.5(H) require risk assessment and worker protection.

If you choose not to do a full review using the five-year clause, take a look at the following higher-risk systems as part of your change management:

• 240V and 208V systems
• Switchgear systems with the newly described horizontal conductor bus configuration

Perform a risk assessment using NFPA 70E-2021 130.5(G) or 130.7(C)(15) and Table 130.5(C). Unfortunately, many workers operate 208V (240V) switches, disconnects or panelboards, and unless the equipment meets the strict requirements of “normal operation,” these tasks will require PPE if the calculation is 1.2 cal/cm² or greater.

Common workwear such as cotton, poly-cotton, polyester or nylon will likely need to be replaced with arc-rated daily workwear. Common daily wear is often life-threatening if ignition occurs. Removing the risk or providing proper PPE is the only alternative.

Use of engineering solutions (primary protection, remote secondary mains, maintenance switches, etc.) to limit worker exposure to 1.2 cal/cm² is the best choice, but this requires a more extensive study and likely some equipment modifications.

Doing nothing is not an option, because there is no grandfather clause on risk assessments for safety. The National Electric Code (NFPA 70) and your local regulations may not require the review, but common sense and the safety standards do.

Editor's note: This article represents the independent views of the authors and should not be construed as a National Safety Council endorsement.