OSHA 1910 Appendix E Table 3 permits single phase arc flash calculations if it can be demonstrated that multiple phases are separated sufficiently. In the case of 15kV+ arc flash studies, ARCPRO is permitted for single phase arc flash studies without having to use a multiplier/conversion factor.

When you put these two together, how does one justify that a 3phase overhead 15kV+ line would likely only result in a single phase arc flash? Is the innate conductor spacing sufficient for this?

For distribution and transmission lines, the spacing between phases is considered too great for an arc to initiate. Good question!

I understood the new rules were intended to encourage covering the unworked phases.

Some make the assumption that if coverups "blankets" are used on the other 2 hot phases, then a 1ph arc will occur. With coverups not used, it is possible multiphase arcs can occur on oh distribution. I suggest reading EPRI Papers, they have tested many real-world utility equipment for scenarios such as this, arcs up to 10 inches and greater may occur on oh distribution. Furthermore, the 2-inch gaps used by ArcPro are much too short for real-world conditions, so you may want to beware of OSHA's Tables that reflect a short, 2inch arc at 15-25kV.
EPRI's lab testing energy results differ quite significantly from industry standards. I believe a new Table may be provided in the next NESC that depicts EPRI's testing results for utility Pad mounted Switchgear and Transformers. Energies 2-3 times larger than what is seen in IEEE Standards resulted from testing on real-world utility equipment. Evidently, NESC subcommittee decided to side with EPRI's results for creation of this new Table for Padmounted equipment and Transformers from 1-35 kV. So do you use NESC tables for padmounted equipment and Switchgear over 1kV, IEEE1584-2018 Standard, or suggested OSHA multipliers to apply to Table 410-2 of the NESC? Good luck with your decision making.

Search for these EPRI papers on IEEE Scholar site:
"Medium-Voltage Arc Flash in Open Air and Padmounted Equipment"
"Comparison of IEEE 1584-2018 Predictions with Tests on Real-World Equipment"
"Medium-Voltage Arc Flash in Switchgear and Live-Front Transformers"


Greg Shirek

A bit off topic, but we have regular incidents (0 to 3 per year) where the wingspan of crows flying through the space between phases on a 24kV overhead feed are sufficient to initiate an arc that takes out the utility fuses.