When using the arc flash PPE category method for AC systems, the fault clearing time has to be greater than the fault clearing time parameter value for the type of equipment to be worked on.

• A. True
• B. False
• C. Not specified
• D. Depends on equipment type

Answer: (B)

Arc flash energy depends on how long the arc lasts, so the duration of the fault (clearing time) directly influences the PPE category you need. When using the arc flash PPE category method for AC systems, a fault clearing time parameter is used as a conservative upper bound for the arcing time to estimate the incident energy. You don’t have to, and should not, require that the actual fault clearing time be greater than that parameter. The parameter represents the worst-case duration you assume to stay within a given PPE category. If the real clearing time is shorter, the actual energy—and the needed PPE—would be lower. If the real clearing time exceeds the parameter, the incident energy could be higher than what the PPE category was based on, possibly requiring a higher level of protection or a more detailed analysis. Therefore, the statement is not correct.