rks wrote:

when i use the "theoretically derived equiation D.7.5B" to calculate AFPB distance and check my answer with SKM software value, my calculated distance is exactly one half the SKM value. anyone have a clue?

I am not sure why it is exactly 1/2 but I would expect the theoretical calculation to be higher. The empirically derived equation is from IEEE 1584 and is based on the normalized incident energy from a prior calculation step.

The normalized Ei uses ARCING current and gap distances. The boundary calculation also uses an X distance factor which is a variation in the theoretical "squared" factor used to account for the incident energy dropping off by the inverse distance "squared". The X is based on the type of equipment and will be less than squared i.e. less than "^2"

The theoretical calculation uses the BOLTED current and ignores most of the details described above.