SheelPandey wrote:

Please help me in understanding that why 70E disallow result of incident energy analysis to specify an arc flash category in Table Method?

Does it mean that calculations for calculating incident energy to get Available Fault Current and Clearing Time at each equipment cannot be used to choose PPE from Table Method? PPE from Table Method cannot be chosen until Available fault Current and Clearing Time is known. Thank you

Two different issues and questions here. As to the former when you do your own calculations, you are altering the assumptions baked into the tables. Doing your own engineering study is just that. You are thus free to adopt your own standards and tables. Annex H is the clothing "table" with just incident energy. Since you are not constrained by the somewhat artificial/outdated 4/8/25/40 selections you can pick values that match the PPE you have or better yet just use incident energy so that you can "future proof" your PPE as the requirements and technology improve over time. Oberon is already kind of walking away from 40 ATPV and offering 41, 43 ATPV in addition to much higher ratings, and there are tested combinations that might make a lot more sense. So there is no value in using the tables if you've done the calculations. Just use Annex H, a risk study, a hazard study, and move on.

As to being "required" to do opening time and available fault current, that is more of an assumption. If you're going to do the calculations, you will significantly improve on the tables and all you are getting is a clothing table so see Annex H. The purpose of the tables is for situations where the engineering calculations are unavailable. Take me yesterday. I went to a customer with a plastic injection molding machine that had a breaker tripping. They barely even got the office set up and had just moved the plant across the country. It was by my count a 4 man operation. Do you honestly think they're going to spend thousands on an engineering study when they didn't even have a place to put a lock on the machine? There was no practical way to do IEEE 1584. So as a service engineer i need some guidance for safety reasons. That's what the tables are for. It might mean I'm moderately underprotected or more likely severely over protected but it's some guidance.

The problem is some users years ago adopted the clothing table and IEEE 1584 instead of Annex H. There is also risk baked into the tables where IEEE 1584 + clothing does not incorporate risk so the rule was promulgated not to mix the two and read the PPE table "backwards". The PPE table is a consequence of the other tables. The ATPV numbers are for selecting PPE, not working backwards from PPE to a calculated value. This should be very obvious because no PPE is required regardless of incident energy under the 2015+ tables or is severely reduced under the 2000-2012 tables.