Protection planning and system design to reduce arc flash incident energy in a multi-voltage level distribution system to 8 CAL/CM2 (HRC 2) or less – part II: Analysis

The paper demonstrates that in a multi-voltage level (medium and low-voltages) distribution system the incident energy can be reduced to 8 cal/cm², or even less, (Hazard risk category, HRC 2), so that a PPE outfit of greater than 2 is not required. This is achieved with the current state of the art equipment and protective devices. It is recognized that in the existing distribution systems, not specifically designed with this objective, it may not be possible to reduce arc flash hazard to this low level, unless major changes in the system design and protection are made. A typical industrial distribution system is analyzed, and tables and time coordination plots are provided to support the analysis. Unit protection schemes and practical guidelines for arc flash reduction are provided. The methodology of IEEE 1584 is used for the analyses.