I know there's a few guys here that have their machines running on phase converters. My utility bill each month is between $500-$600 and I only run the machine after work and on the weekends. Maybe 40 hours max or so per week. There's been many weeks that I didn't even start the thing too. The machine is an '07 VF-2ss running on a 50hp American Rotary phase converter.

The majority of my work is prototyping and very small runs (max of 10 parts on average) so the machine is sitting idle quite a bit, and the biggest cut I take for the most part has the spindle at 50%.

I took some amp readings today and will share the results. I'm no electrician, so hopefully I did everything correctly. The way I measured amperage is with a clamp-on amp probe clamped onto one of the wires coming from the main panel into the phase converter.

At idle, it pulls 14A per leg.
Starting spindle from 0 to 12k rpm pulls 140A per leg (200% spindle load).
12k rpm steady state pulls 18A per leg (3% spindle load).
12k rpm, 50% spindle load cut pulls 27A (50% spindle load).

I used this formula to come up with Killowatts:
Amps per leg x 2 legs x voltage (240) /1000 = killowatts.

We get charged roughly $0.20 per kwh. So worst case scenario, if I roughed something out at 54A for 40 hours/week that would cost me $415 over and above our regular house usage. That works out to taking up $11 of my hourly rate. Not bad, but I don't use the mill like that. A big chunk of its time is sitting idle while messing with programs, changing offsets, etc. That, and the majority of the tooling I run is 1/4" and smaller, down to very small endmills. I'll see 3-5% spindle loads for hours on end.

What are your thoughts? Is this in line with what everyone is seeing?