Arc Flash Boundary

The arc flash boundary defines the safe working distance around energised equipment where an arc flash event could cause burns. At distances greater than the boundary, incident energy is below 1.2 cal/cm² and the risk of second-degree burns is minimal for unprotected skin. Inside the boundary, the incident energy increases rapidly with proximity, and arc-rated PPE must be worn. The boundary distance depends on the available fault current, protective device clearing time, electrode gap, enclosure dimensions, and electrode configuration. Typical arc flash boundaries range from a few centimetres for low-energy circuits to several metres for high-current switchboards with slow-clearing protection. Reducing the arc flash boundary — and the associated PPE requirements — is a key goal of arc flash mitigation strategies. Methods include reducing clearing time through faster protective devices, lowering the available fault current by adding current-limiting reactors, increasing the working distance, and installing arc flash detection systems that can trip the supply in under 5 milliseconds. Labels on switchboards must display the arc flash boundary, incident energy at the working distance, and required PPE category to inform workers before they approach energised equipment.