NFPA 70E has developed requirements to reduce the risk of injury to workers due to shock and arc flash hazards. There are three shock approach boundaries (limited, restricted and prohibited) required to be observed in NFPA 70E 2000. The limited, restricted and prohibited approach boundaries are based on the voltage of the energized equipment. Also, NFPA 70E 2000 requires that before a worker approaches exposed electric conductors or circuit parts that have not been placed in a safe work condition, a flash hazard assessment must be performed. Until equipment is placed in a safe work condition (NFPA 70E 2000 Part II 2-1.1.3), it is considered live. It is important to note that conductors and equipment are considered live when checking for voltage while putting equipment in a safe work condition. The arc flash hazard analysis should determine the arc flash boundary (AFB) and level of personal protective equipment (PPE) that the worker must wear. The arc flash boundary is based on voltage, the available fault current and the time it takes for the upstream protective device to operate and clear the fault. The boundaries are summarized below:
© 2015 ARCAD INC. All rights reserved.