Any thoughts on using the 1.5 to 4 cycle fault contributions vs the 1/2 cycle?

I have wondered a little about this myself. What is the correct fault duty to use for the short circuit calculation when doing arc flash studies?

I can tell you that when I started doing arc flash studies, we used ETAP to do the short circuit study, but had to do the arc flash calc using the IEEE spreadsheet, and calculate the trip time using TCC's, I was told to use the 1.5-4 cycle calculation in ETAP. I'm not sure what the reasoning was behind it, though, except that this may have produced a better (more realistic) current level by which to find trip times.

In the help file for the Acr Flash Case parameters it says, "If this option is selected, the module will use the symmetrical 1.5 to 4 cycle 3-phase (interrupting) fault current to determine the fault clearing time and the incident energy for medium voltage elements (above 1.0 kV)."

Note the above 1000V. Does this mean that for medium voltages less than 1000V (480V & 600V) we should use the 1/2 cycle?