Section 5.1 of IEEE 1584 defines the voltage range as below:

[*]Voltages in the range of 208 V–15 000 V, three-phase.

Does it means phase to phase voltage or phase to ground voltage? I understand that single phase arc quickly evolves into three-phase arc per IEEE model but does it true single phase to ground mean phase to ground voltage? If that is a case, then 25kV system with single phase to ground less than 15kV would be appropriated to apply IEEE 1585 instead of Arcpro which conflicts with OSHA software recommendation.
=============================

That is the 3 phase voltage which is phase to phase to follow convention.



Not sure what you are asking here. Please clarify.



This is a moot issue since it is answered above as it is 3 phase voltage and would fall into the More than 15 kV column in OSHA Appendix E Table 3.

By definition, an electric arc is a visible plasma discharge between two electrodes that is caused by electrical current ionizing gasses in the air



Varc < 15kV between two un-grounded conductors



25kV nominal voltage system with single phase to ground arcing ==> Varc < 15kV between un-grounded and grounded conductors

I understand the technical wording but my gut didn't feel the same.