Figure out what you pay per kW/hr
Find out the amps of (and voltage of) your plasma cutter under load (at the wall)
Find out how many amps (and voltage of) your compressor uses (at the wall)
Estimate a duty cycle for your compressor. Does it run all the time you cut? 50% of the time? 20%?
{(Cut time in hrs * plasma amps * plasma volts) + (cut time in hrs * compressor duty cycle * compressor amps * compressor volts)} *.001 * cost per kW/hr
Example:
¢10 per kW/hr
Plasma: 30A @220v
Compressor: 16A @220v @25%
Cut time: 6min
{(.1 * 30 * 220) + (.1 * .25 * 16 * 220)} * .001 * ¢10 =
(660+88) * .001 * ¢10 = ¢7.48
Or just make a wild a$$ guess and build it into your hourly rate. I’ve not included the table, because it’s a fraction of what the plasma and compressor use.
Even a large plasma and compressor combined with the table would have trouble pulling $2-3/hr in electricity at ¢10-20 per kW/hr.