Megohmmeter Model 1015
17
4.2.6 Insulation Resistance Measurements on Motors
Figure 8 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 8
Figure 9 shows the wind-
ings of a three-phase
motor separated.
Sometimes this can be
done at the lead termi-
nals, while other times
the end bells must be
removed to get at the
lead wires of the coils.
By connecting the meg-
ohmmeter as shown, the
phase insulation resis-
tance value can now be
determined.
Read between phases “A” and “B”,
then “B” and “C”, then “C” and “A”.
OFF
M
Ω
- 1000 V
M
Ω
- 500 V
1000
Ω
AEMC
I N S T R U M E N T S
MEGOHMMETER
M O D E L 1 0 1 5
Battery
Check
10
Ω +
10
Ω −
0.1
0.5
1
5 10
50 100
500
1000
0
1
2
3
4
5
6
7
8
9
10
0
100
200
300
400
500
600V
600V
-
+
6
!
M
Ω
A
B
C
+
-
Figure 9
+
-
OFF
M
Ω
- 1000 V
M
Ω
- 500 V
1000
Ω
AEMC
I N S T R U M E N T S
MEGOHMMETER
M O D E L 1 0 1 5
Battery
Check
10
Ω +
10
Ω −
0.1
0.5
1
5 10
50 100
500
1000
0
1
2
3
4
5
6
7
8
9
10
0
100
200
300
400
500
600V
600V
-
+
6
!
M
Ω
