they uses an ungrounded system like westinghouse did. they want to isolate the 24v circuits from earth ground because of possible induced voltage into the circuit. If you have C24, M24, or H24 going to earth ground the elevator could possibly move on its own while you have control of it on car top or hoistway inspection. It won't pop the breakers because REF on the power supply isn't grounded to earth ground BE CAREFUL