The Gap distance affects the arcing short circuit current and ultimately the incident energy. It is understood, that the greater the gap, the more difficult it may be to sustain an arc flash.

The IEEE range of gaps for 208 V to 600 V is: 0.25 in to 3 in (6.35 mm to 76.2 mm)
IEEE 1584 Table 8 suggests gaps of 1 inch (25 mm) to 1.25 inches (32 mm) for low voltage equipment - Panels and Switchgear

However, equipment such as pad mounted transformers can have gap distance significantly greater than those values.

Here is this week’s question:
For the secondary of pad mounted transformers do you use ACTUAL GAP or IEEE 1584 gap?
Actual gap distance
IEEE 1584 gaps 0.25 to 1.5 inches
IEEE 1584 gaps between 1.5 and 3 inches
It depends
I don’t perform studies

Your thoughts are always welcome!

The problem I have found is that the gap is usually greater than the max suggested by IEEE 1584.

I use NESC. (I understand they are redoing the low voltage table for 2023. I haven't seen it yet.)

It occurs to me the initial gap would actually be zero when a worker accidentally brings a grounded conductive object into contact. The gap then widens as the worker pulls away. One of our workers actually did this and singed his eyebrows and ruined his safety glasses and I suspect his underwear. I don't believe the primary fuse cleared and the arc did extinguished once the gap increased sufficiently.

I think using the IEEE gaps makes more sense.