70e: arc flash PPE table method or incident energy analysis for low voltage equipment?
NFPA 70E nerds: anyone here NOT using the arc flash PPE table method (130.7 c) for lower voltage equipment (doing incident energy analysis instead)?
Seems like a lot more work to do the incident energy analysis so I’m wondering what the main benefits of the calculation are over the table method
Comments (3)
The hazard category method is a lot more conservative. If you're following NFPA 70E, an incident energy analysis is required every 5 years, so that would be much more accurate than the category method. The category method is only to be used if you don't have the incident energy analysis done (which if you don't, then you're out of compliance anyways).
Table 130.7(C)(15)(a)/(b) only tells you the minimum arc ratings (cal/cm2) for your PPE based on conservative approaches, so it may be overkill for what you need, whereas the incident energy analysis will tell you the exact arc rating(s) you need. If you've ever been in an arc flash suit (especially 40 cal or higher), then you'll know that the lower cal suit you have, the more comfortable they are. The higher cal suits are hot and uncomfortable, even the ones that have internal, built-in fans.
I always think of an arc flash as being like a bomb. The incident energy tells you how big of a bomb you have. Do you have a firecracker? Or do you have C4? With the category method, you're just essentially guessing at it.
Also, keep in mind that whether it's low voltage or not pertains more to your shock hazard, rather than your arc flash hazard. The arc flash hazard is based on not only the voltage, but also the bolted (short-circuit) fault current and clearing times of the OCPDs.