One reason why you sometimes see higher ratings required for inverter power supplies is if they are designed to switch on at full load. The kinds of VFD/inverter you use with these spindles will ramp up relatively slowly, though, and that keeps the initial surge under control which might otherwise trip a breaker. My machine runs off a single 13A socket with VFD, PC, stepper drivers, etc, all running from that. The same ring supplies the wet-and-dry nominal 1200W vacuum cleaner for dust extraction, and I have never had a problem with any of that. The garage ring is separate from any of the house ring circuits, to avoid the kinds of problem that Jazz mentions (and the possibility of a problem with a machine in the garage tripping the house ring that feeds the television or my wife's sewing machine, which could lead to drastic loss of privileges).