I’d like to ask something on this if you don’t mind because standards are expensive and the last time I bought a NFPA 70E book was for 2015. 70 110.16 B includes a requirement for marking the clearing time of the circuit breaker and it was discussed here that this can be used for if you reference the 70E section 130 tables for classification of hazard and ppe selection. But unless the 70E standard has changed I don’t recall the tables in section 130 including the clearing time of a circuit breaker in the selection criteria for PPE. Do you know if they have changed or will change in the 2021 standard, to include this?

Secondly, for getting the clearing time of an inverse time circuit breaker under fault, what is really the practice for doing this? It’s an inverse time circuit breaker so it’s clearing time is going to be dependent on the systems ability and how much fault this current system provides. On the services over 1200 A that I have done there’s always been an arc flash study so this was never something that was considered by field personnel.

BTW: I think there may be a good reason 70E wouldn’t want people using clearing time in ppe selection using just the tables. That being because while it is not difficult to calculate infinite bus through a transformer, any calculation relying on clearing time of circuit breaker has to consider the condition of maintenance of the circuit breaker (also part of the NFPA 70 E standard’s requirements) and so having a label that marks the mfr standard clearing time and using it for a field calculation that is not done as part of a once every 5 year arc flash study could come with a risk of underestimating the hazard. Using infinite bus comes with less risk of under-classifying the hazard of working in an environment where there’s no arc flash study/label.

Thanks