Test Instruments & Measuring Devices
OTHER ELECTRICAL MEASURING DEVICES
In the ohm meter method (Figure 15), a DC voltage is applied to the conductor. If a leakage
path exists between the conductor insulator and ground, a current will flow through the ground
to the ohm meter proportional to the insulation resistance of the conductor.
Figure 15 Simple Ohm Meter Ground Detector
In the ground detector lamp method (Figure 16), a set of three lamps connected through
transformers to the system is used. To check for grounds, the switch is closed and the brilliance
of the lamps is observed. If the lamps are equally bright, no ground exists and all the lamps
receive the same voltage. If any one lamp is dark, and the other two lamps are brighter, the
phase in which the darkened lamp is in is grounded. In this case, the primary winding of the
transformer is shorted to ground and receives no voltage.