Electronic Electrical Devices | Electronic Electrical Components
D'Arsonval Movement Meter
A electrical ground meter is an instrument which is used to detect conductor insulation resistance to
ground. An ohm meter, or a series of lights, can be used to detect the insulation strength of an
ungrounded distribution system. Most power distribution systems in use today are of the
grounded variety; however, some ungrounded systems still exist.
In the ohm meter method illustrated below, 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.
Ohm Meter Method
In the ground detector lamp method (shown below), 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.
Ground Detector Lamp Method