"If I understand you correctly, a DMM would measure a percentage of supply voltage from L1 to grnd and N to grnd because of the ground detection device (Line Isolation Monitor?) but if it were out of the circuit then there would be zero voltage measured?"
That's right, your measured voltages should be close to zero. Also, with the 2-pole breaker for the ground detector off, I'm guessing that you would measure a resistance through the detector that is substantially lower than your meter input impedance.
Joe
