[Al Skierkiewicz]

As a caveat, the resistance across the 120 amp breaker varies with temperature and manufacture. A one foot length of #10 wire is very close to 1 milliohm. Placed in the power return at the input of a speed controller allows one to measure input current, of constant polarity, at 1mV/A. Sample at 500 Hz or higher and throw away measurements that are less than 20mV and you will get a pretty good idea what the current is.