I have never tried to run them "unbalanced", but the electric company put in a new sub station on my line a couple of years ago, which causedthe inbound single phase 220 to change voltage values (I am on a rural line). I dont rember the exact alarm number but it alarmed (and it was electrical supply flagged) as soon as I tried to power up. I had to go with another tap on the transformer and re-balance the caps. they were 11 and 12 between phases and I ended up with 9 and 14 IIRC (these are 50mf units) to get back in balance. Since that no problems. My CNC's use almost no "real" 3-phase, nearly everything except the hydraulic, coolant, and chip auger motors is DC. The spindles use a thyristor to control them. If your CNC does enough internal conditioning you could get away with unbalanced 3ph, but most (in my experience anyway) don't, and you are taking a chance with some very expensive components IMHO. Caps, even run caps, are a lot cheaper than boards.