A few months ago, I participated in a Q&A webcast aimed at a little game of what I like to call “stump the instructor.” Of course, since I am an electrical safety professional, the questions were based on major electrical safety topics. While there were a ton of great questions from the moderator and audience, there was one question that really stuck with me: when it comes to arc flash studies, how do we determine which are useful and which are not?

As an electrician, I was trained to understand that the incident energy value on the arc flash label was determined by expert engineers and software that provides an accurate estimate of how much thermal energy would be released during an arc flash event. This was a great way to determine what arc-rated clothing I needed to wear to protect myself from severe burn injuries that often follow such an event. I never questioned whether the label might be misleading or inaccurate. That is, until I started doing a few electrical safety and maintenance audits.

Qualifications to do calculations

The first thing I started to question was the qualification of the engineer or person that performed the calculation. NFPA 70E and OSHA do not require that the calculation be performed or even reviewed by a licensed professional engineer. This surprised me at first, but it made sense that it was up to the employer to determine how to approach this calculation. 

The specific incident that drew my attention to this was at a generation plant where the electricity connected to the grid at more than 100,000V. I saw there was an arc flash hazard label with an incident energy value of more than 1,000 cal/cm²! 

However, on further investigation, I noticed this was on an operating handle for an overhead switch in the switchyard. The label stated that this extreme incident energy value was calculated at a working distance of 18 inches, and the switch was a good 30 feet from the overhead lines. Clearly, the person that performed this incident energy study was not paying attention or did not understand what they were doing. Who we choose as the person or firm performing it is nearly as important as doing the calculation itself.

Reviews for accuracy

Another area that might support my trust in an arc flash study is whether it has been reviewed for accuracy. NFPA 70E states that this must take place at a minimum every five years. However, we need to update our studies whenever something changes in the electrical distribution system that might affect the results. 

Maybe a large motor load has been added to the system, or a transformer has been replaced with one of a lower internal impedance. There are several examples that can affect how much fault current flows during an arc flash. This review is critical to ensuring the accuracy of an arc flash study. Every five years might be sufficient if nothing changes, but this interval doesn’t work if something has been altered.

Maintenance

Finally, and likely the most common reason I question the accuracy of an arc flash study, is maintenance. Most important, I ask, what maintenance has been performed on the OCPD that was previously valued? 

Just as critical to the amount of fault current available is the clearing time of the upstream OCPD. We want the OCPD to be able to clear an arc fault as quickly as possible, and the clearing times advertised by the manufacturer are based on the device being properly maintained for the duration of its life cycle. However, a lack of maintenance often leads to longer clearing times or the inability of an OCPD to clear a fault at all. This is especially true in the case of circuit breakers, as there are mechanical components inside the device that stiffen up over time. 

Additionally, performing and tracking maintenance over the life of an OCPD allows us to monitor the health of the circuit breaker. One major question maintenance will help us answer is, “How many fault events has the circuit breaker opened in the past?” Many folks are completely unaware of the fact that a circuit breaker is only rated to open a handful of faults before it is no longer reliable.

When it comes to relying on the arc flash label to accurately portray the necessary information workers need to address arc flash hazards, these are just a few of the questions that come to mind. The arc flash study results are only ever as accurate as the information going into it. Therefore, it is imperative to stay on top of systems by performing regular maintenance and updating the results when changes occur that affect incident energy values.

Performing the review of the arc flash study on a minimum 5-year basis keeps us confident in the accuracy of this critical piece of the electrical safety world. And if the review shows that the values are still accurate, the worst-case scenario is that we just took the time to validate what we already learned. Without the review, there are far too many questions for this electrician to risk my health and safety.

Until next time, remember to stay safe and always test before you touch!

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