To make things more complicated, since we are protecting ourselves from a different hazard, the PPE requirements also differ. The arc flash boundary, however, may be greater than, equal to, or less than either of the restricted or limited approach boundaries. With shock boundaries, we know that the restricted is always closer than the limited. Since the calorie ratings of equipment are not nearly as uniform as the voltage ratings, the arc flash boundary has a much wider range of possibilities. Unlike limited and restricted boundaries, which are dependent on voltage, the arc flash boundary is dependent on the incident energy or calorie rating at the equipment. The arc flash boundary is an approach limit from an arc source at which incident energy is high enough to cause a second-degree burn. Now let’s introduce the Arc Flash Boundary. That 12 inches would be your trigger point for shock PPE such as voltage-rated gloves and/or insulated tools.

The restricted approach boundary would be 12 inches. The limited approach boundary will be 3’6”, which means that only you, the qualified worker doing the work, can enter. Let’s assume that you are a qualified worker and are tasked with taking a voltage reading on a 480V disconnect. For 50V to 150V, the restricted approach boundary is to avoid contact with the circuit parts. This protection is usually in the form of voltage-rated gloves with leather protectors and/or insulated tools. This boundary is only to be crossed by qualified workers and the worker must be protected from unexpected contact. The Restricted Approach Boundary is the 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. Let’s go into a little detail on each of these. They can be found in Table 130.4(D)(a) for AC and 130.4(D)(b) for DC circuits. If you have had an arc flash risk assessment performed, these approach boundaries are on your equipment labels. Since these boundaries are for shock, they are determined solely on voltage which makes them very straightforward. Take note that the Restricted Approach Boundary and Limited Approach Boundary are shock boundaries and have nothing to do with arc flash. Limited Approach Boundary (for shock protection only)Īrc Flash Boundary (for arc flash protection only) Restricted Approach Boundary (for shock protection only) Let’s start with an introduction of the three electrical approach boundaries: More importantly, because it is easy to follow, it is more likely to be followed. I’ve said many times that it’s complicated to explain, but it doesn’t have to be complicated to implement. A panel or task that has a high shock risk might have a low arc flash risk and vice versa. Afterall, the risk for shock and the risk for arc flash are not the same. Therefore, the protective equipment is different for each event.Īs a result, it would be a mistake to create a blanket system that requires us to wear a full arc flash suit every time we approach electrical equipment.

As discussed in earlier articles, shock and arc flash are different events with different injuries and different ways of causing death. The complication arises from the fact that we are trying to protect ourselves from not just one, but two potential hazards-shock and arc flash. In fact, four approach boundaries were taught when I first learned about approach boundaries, until the Prohibited Approach Boundary was deleted in 2015. Why does everything have to be so complicated? When I first introduce the concept, I often get these questions: It’s not that learning approach boundaries is above anyone’s head, but more to do with the fact that there are three different approach boundaries. Approach Boundaries can be one of the most difficult topics for me to explain in my electrical safety classes.

Arc flash boundary 480v