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Working distance is defined as the closest distance to a worker’s body excluding hands and arms. IEEE 1584 Guide [9] specifies required working distances (Table 1.6). For the 15-kV switchgear, it is 36 in, while for a 480-V MCC, it is 18 in. A larger working distance reduces the incident energy and therefore the HRC. Recommendations of IEEE for the working distances are followed in the calculations in this book. The working distance does exclude hands and arms, which will be much closer to the seat of arc. It is the vital organs like eyes, chest, and heart that are at the working distance from the seat of the arc. This assumes that a worker does not stick his head inside the switchgear door!