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The Incident Energy Analysis Method versus Arc Flash PPE Category Method

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Bobby Lindsey

President

Let’s Review the Two Ways of Selecting Arc Flash PPE
The Incident Energy Analysis Method versus Arc Flash PPE Category Method

Selecting the proper Arc Flash PPE can be confusing. With terms such as incident energy, calories, and hazard risk categories, it can become complicated. Complicated is not a good thing when it comes to safety, especially electrical safety. The goal is to protect ourselves from electrical hazards while keeping the process as simple as possible. Overcomplicating safety measures often leads to ignoring safety measures.

The focus of this week’s article is to explain, in the simplest terms, how to select the proper PPE to protect against arc flash hazards.

There are two ways to select arc rated PPE:
1. The Incident Energy Analysis Method
2. Arc Flash PPE Category Method

Both methods have their own advantages and disadvantages, but both are effective. To decide which method to choose for your team, we are going to look at each of them in more detail.

Incident Energy Analysis Method

This method involves using incident energy to determine the risk of an arc flash and the distance of the arc flash boundary. NFPA 70E defines incident energy as “The amount of thermal energy impressed on a surface, a certain distance from the source, generated during an electrical arc event. Incident energy is typically expressed in calories per square centimeter (cal/cm2).”

An arc flash risk assessment of the electrical distribution system is used to calculate the incident energy and determine the arc flash boundary. Both values can be found on the arc flash labels that are applied during the assessment. The worker selects PPE that is rated equal to or greater than the incident energy value and uses the arc flash boundary as the trigger point for the PPE. See figures 1 and 2 below for examples.

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Arc Flash PPE Category Method

Unlike the incident energy analysis method, the PPE category method does not involve calculations. This method uses tables to estimate the risk based on maximum available fault currents, clearing times of overcurrent protective devices such as breakers and fuses, and working distances. If known, the fault currents at the equipment and clearing times are cross-referenced with the tables to determine the arc flash PPE category and arc flash boundary. Using this method, the arc flash labels will identify the PPE Category rather than the incident energy. Figure 3 provides an example.

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If no arc flash label exists, the PPE Category method must be used. The worker must know the available fault current and clearing times and use NFPA 70E Table 130.7(C)(15)(a) for ac systems and 130.7(C)(15)(b) for dc systems to determine the arc flash category and estimate the arc flash boundary. The worker then uses NFPA 70E Table 130.7(C)(15)(a) to determine the PPE requirements for that category level. This can get complicated.

Which Method is Right for You?

Whether you choose the Incident Energy Analysis Method or the Arc Flash PPE Category Method, you must choose one and only one. Each method has pros and cons.

The Incident Energy Analysis Method can become expensive because it requires an arc flash risk assessment and extensive data collection to calculate the incident energy. However, this method usually involves arc flash labels which makes compliance with a PPE policy easier. In addition, only one NFPA 70E table, Table 130.5(G), must be referenced.

On the other hand, the Arc Flash PPE Category Method uses up to three tables as reference points. Furthermore, many times the facility does not have arc flash labels on equipment. If this is the case, the worker is required to know the fault current and clearing times of the equipment. If this is not known or these values fall outside the parameters of the NFPA 70E tables, this method cannot be used.

In my opinion, the Incident Energy Analysis Method is the safest, most accurate, and easiest to follow of the two methods. Implementation can be expensive, but I believe the cost is easily overcome by the benefits. The graphics below outline the pros and cons of each method.

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Thank you for your time. Mitchell & Lindsey offers Arc Flash Risk Assessments and Electrical Safety Training. If we can be of service to you in these areas or if you have any questions about this article, please reach out to me at the email or phone number below.

Don’t forget to check out our other articles and videos at www.mitchellandlindsey.com/resources. 
Thank you and be safe!
Bobby Lindsey – CESCP
Mitchell & Lindsey – President
M: (502) 836-4217
email: blindsey@mitchellandlindsey.com

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