During my career, I have learned about the importance of establishing strong boundaries with co-workers and communicating that there are certain lines that cannot be crossed under any circumstances. Of course, I am talking about my shock approach and arc flash boundaries!

All joking aside, when it comes to electrical safety, there are few concepts as important as the approach boundaries outlined in NFPA 70E: Standard for Electrical Safety in the Workplace. The standard uses these boundaries for everything from defining when a shock hazard is present to outlining when and where arc-rated PPE must be worn. They are a cornerstone of NFPA 70E’s practical process for creating a safe workplace relative to the hazards arising from the use of electricity.

Shock approach boundaries

First, let’s examine the shock approach boundaries. NFPA 70E sets two separate distances with respect to electric shock hazards: the limited approach boundary (LAB) and the restricted approach boundary (RAB). Article 100 defines the LAB “as an approach limit at a distance from an exposed energized electrical conductor or circuit part within which an electric shock hazard exists.” The RAB is defined “as an approach limit at a distance from an exposed energized electrical conductor or circuit part within which there is an increased likelihood of electric shock, due to electrical arc-over combined with inadvertent movement.”

There are some key terms in each definition—for instance, the word “exposed,” as in “distance from an exposed energized electrical conductor or circuit part.” Of course, by digging a little further into Article 100, we’ll find a definition of this term. Exposed, as it applies to energized electrical conductors and circuit parts, is defined as “capable of being inadvertently touched or approached nearer than a safe distance by a person. It is applied to electrical conductors or circuit parts that are not suitably guarded, isolated, or insulated.”

To be clear, neither the LAB nor RAB exist without first identifying if there are exposed energized conductors or circuit parts. Then we can unpack the rest of the LAB definition. The LAB is the distance from exposed energized parts within which there is a shock hazard. In practice, this means that when trying to determine whether a shock hazard is present in the task at hand, we must answer if exposed parts are present and if the task will take us inside the LAB. If the answers to both questions are yes, then a shock hazard is present.

The RAB, however, places emphasis on the likelihood of being shocked, either because we make contact or are close enough for the electricity to reach out and touch us. In practice, NFPA 70E requires an electrically safe work condition (ESWC) if an employee is performing work within the LAB because a shock hazard simply exists or if there is justification for the equipment to remain energized by meeting one of the exceptions to 110.2(B). To create the ESWC, we must either insulate any part of the body that crosses the RAB or insulate the parts from us.

The good news is that NFPA 70E makes it easy to determine these distances thanks to two tables found in Section 130.4(E). Note the tables are broken up for AC and DC systems. These distances are based on the system’s phase-to-phase voltage and are easy to look up once this value is known. However, when it comes to the LAB, these tables do set different distances based on whether the exposed energized circuit parts are fixed in place or are movable conductors. If the position of the energized electrical conductors is not fixed, the distance within which an electric shock hazard exists is much greater than when the parts can’t move.

Electric shock risk assessment

These boundaries are important in an electric shock risk assessment and must be used to determine if a hazard exists and the likelihood of being shocked. Failure to understand that the shock hazard begins at the LAB has exposed countless employees to potential danger and has led to confusion as to when an ESWC must be established. Part of being a qualified person is knowing when the need arises to create an ESWC versus when we can perform energized work.

Remember, as a qualified person, it is not just the RAB that is of concern. If we apply these two shock approach boundaries the way they are spelled out in NFPA 70E, we gain valuable insight into how the standard approaches electrical safety. If a hazard is present in the work, the priority is to shut it down (de-energize), make sure it can’t come back on (lockout/tagout) and verify it is in a zero-energy state using the live-dead-live process for absence of voltage testing.

Stay safe, and always remember to test before you touch!

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