Customer has a nest thermostat on top floor and didn’t have any power from C wire from new air handler we installed, checked voltage a outlet on ply which had 120 volts, checked voltage going to transformer in unit and didn’t have any power, tried to check incoming voltage from switch to unit and wires arced, found line voltage wire coming into unit had broken off causing no power to unit, respliced wires and tested thermostat, which now had power and thermostat has to charge but all indicator lights working as it was doing nothing before, system operational.