The fundamental rule in all codes and standards is: Before opening any enclosure that may contain exposed energized circuit parts or equipment, or approaching exposed energized conductors or equipment, the equipment shall be de-energized. Additional material in the NFPA Standards and in OSHA define a qualified person as one who has received documented training in the hazards of working on energized equipment in general, and has been trained in the hazards of the particular equipment to be serviced. Protection boundary to be crossed by only qualified persons (at a distance from a live part) which, due to its proximity to a shock hazard, requires the use of shock protection techniques and equipment when crossed.” To cross the Restricted Approach Boundary into the “Restricted Space”, in addition to the PPE and required training, a qualified person must have a documented plan approved by management, and plan the work to keep all parts of the body out of the “Prohibited Space”. When the arc current exceeds the current-limiting threshold of the fuse, the amount of arc current is greatly reduced, and the circuit is opened in less than ½ cycle (0.0083 seconds) In many cases, opening time may be ¼ cycle (0.004 seconds) or less. While no protective device can totally eliminate the hazards, proper fuse application will reduce the hazard, and help simplify the selection of PPE. In order to properly apply fuses or circuit breakers, the available fault current must be determined at each point where workers may be exposed to energized circuits, the arc energy must be calculated, and the opening time of the protective device determined.
Although we’ve had numerous posts regarding arc flash, the danger involved merits so many conversations. L&S Electric conducts Arc Flash Surveys to help save both you and your equipment.