scjohn, I did a search here on this site, and there was talk of derating phase convertors, up to 57%....
I have very limited experience with these, but will tell you, rotary convertors put out a high leg, and this should not be used for control circuits. If your equipment is "vital and expensive" as you say, then Larry's advise would be prudent. Contact both, the convertor manufacturer and the equipment manufacturer prior to installation.....
Dnk...