AEMC 1000N - Insulation Resistance Measurements on Motors

Megohmmeter Model 1000N/1100N
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Figure 12 shows reading the
resistance to ground of a three-
phase motor winding. Since the
three-phase motors are internally
connected, it is only necessary to
connect one lead to the motor lead
and the other lead to the motor
frame as shown.
Figure 12
Figure 13 shows the
windings of a three-phase
motor separated. Some-
times this can be done at
the lead terminals while
other times the end bells
must be removed to get at
the lead wires of the coils.
By connecting the megohm-
meter as shown, the phase
insulation resistance value
can now be determined.
Read between phases “A”
and “B”, then “B” and “C”,
then “C” and “A”.
Figure 13
+ EARTH- LINE
MEGOHMMETER
GUARD
+ EARTH- LINE
MEGOHMMETER
GUARD
A
B
C