Where are barricades to be placed for electrical safety? Are the barricades to be placed at the limited approach boundary? What is the difference between the limited approach boundary and arc flash boundary?
Limited approach boundaries are determined by the maximum operating voltage and therefore do not change. For example, the limited approach boundary for 4160 V is 60 inches. The arc flash boundary is determined by the available fault current and is found on the equipment's arc flash label. On some of our MCC and switchgear equipment, the arc flash boundary is in the 17 feet category. Barricades should be set just outside the greatest boundary indicated (voltage or arc flash). The purpose of the barricade is to keep unqualified or unprotected personnel from crossing into the work space during a dangerous activity or when we have exposed live electrical parts.
Sometimes, we've found that the arc flash hazard requires us to barricade the entire MCC. You are at your greatest exposure for an arc flash when racking a breaker or removing/inserting a motor control bucket with a live bus. Using remote racking equipment, a Chicken Switch, remote closure panels, and arc reduction maintenance switches are some methods of reducing and/or eliminating personal exposure, as is wearing appropriate arc flash and shock PPE when these are not in use. However, that does not mean that the potential for an arc flash or shock does not exist during diagnostic activities such as taking voltage readings or amp checks on a running piece of equipment. Each task and associated activity should be evaluated using a hazard/risk assessment and proper planning is the key to safety.
The safest approach is to ALWAYS DE-ENERGIZE. At no time can we ever expose ourselves to greater than 40 cal/cm2, and anything over 50 V requires shock protection in the form of rubber gloves with leather protectors. I hope this helps. Stay safe!
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