Voltage does not determine the arc flash hazard. Knowing the voltage is only one piece of determining Arc Flash PPE. The electrode orientation, available fault current (amps), the working distance between the worker and the equipment, the clearing time of the circuit protection device, the spacing between conductors or from a conductor to ground, the number of phases, whether the conductors are in an enclosure, and the equipment configuration must all be considered when determining the potential severity of an arc flash hazard. NFPA 70E provides two methods for the selection of arc flash PPE as part of an overarching requirement to complete an arc flash risk assessment. The two selection methods are;
- Incident energy analysis method. Often referred to as an “arc flash study”, requires engineering calculations to determine the potential thermal incident energy in the event of an arc flash. Arc flash PPE is then selected so the arc rating (protection) matches or exceeds the calculated incident energy. Both the thermal incident energy and protective arc ratings are calculated as calories per square centimeter (cal/cm2).
- Arc flash PPE category method. Otherwise known as the “table method”, involves a simplified approach using the tables from within the Standard to determine a category number from 1-4 and corresponding arc flash PPE minimum requirements. The table method requires validation of the parameters used in the creation of the categories, otherwise the user is forced into using the incident energy analysis method. Refer to Oberon’s catalog on page #5 for arc flash PPE category product information.
Either, but not both, arc flash PPE selection methods can be used on the same piece of equipment. The engineering calculations used in the incident energy analysis method cannot be used to specify an arc flash PPE category. Keep both methods separate and document your decision making processes within your company’s Electrical Safety Program.
The bottom line is that you can’t rely on voltage alone to figure out what arc flash PPE you need. NFPA 70E requires the employer to complete an arc flash risk assessment. If additional protective measures are required, arc flash PPE can be applied as a control to mitigate the risk of an arc flash. Refer to the latest edition of the NFPA 70E Standard to learn more about the requirements for an arc flash risk assessment.