10
Motors
AC - Disconnect the motor from the line by disconnecting
the wires at the motor terminals or by opening the main
switch. If the main switch is used and the motor also has a
starter then the starter must be held, by some means, in
the ON position. In the latter case, the measured resistance
will include the resistance of the motor, wire and all other
components between the motor and the main switch. If a
low insulation resistance reading is indicated, the motor
and other components should be checked individually. If
the motor is disconnected at the motor terminals, connect
one megohmmeter lead to the grounded motor housing
and the other lead to one of the motor leads.
DC - Disconnect the motor from the line. To test the brush
ring field coils and armature, connect one megohmmeter
lead to the grounded motor housing and the other lead to
the brush on the commutator. If a low insulation resistance
reading is indicated, raise the brushes off the commutator
and separately test the armature, field coils and brush ring
by connecting one megohmmeter lead to each of them
individually, leaving the other connected to the grounded
motor housing.
Note: The above also applies to DC generators.
1065DGMAN_20250-60 DS Insulation tester manual.indd 10
8/7/2017 2:09:50 PM
