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INSULATION TESTING
34.
For the necessary inspections and insulation testing one tool is required:
Insulation measuring tester (Megaohmeter) unit 5OOv test, display up to min 200 M Ohm .
The correct execution of the junction (hermetic sealing) can be verified testing it under water for at least 15 min and
measuring with the Megaohmeter the insulation resistance between the metal recipient, filled with water (or water
itself) and each of the phase wires of the cable connected to the motor.
For a new motor the correct measurement has to be at least 200 M Ohm.
Another measure has to be done before installing the motor / pump in the place of use:
1
connect a measuring cable to the ground lead
2
connect the other measuring cable to each conductor of the connected motor cable.
The exact values have to be at least 200 M Ohm for a new motor, and 20 M Ohm with a used motor installed.
It is always suggested to repeat this operation various times while lowering the motor/pump in the well.
35.
RESISTANCE OF THE DROP CABLE
The values below are for copper conductors. If aluminum conductor drop cable is used, the resistance will be higher.
To determine the actual resistance of the aluminum drop cable, divide the ohm readings from this chart by 0.61.
This chart shows total resistance of cable from control to motor and back.
Resistance in ohms per 100 ft of Wire @ 50 °F
Table 22: DROP CABLE RESISTANCE
AWG WIRE SIZE (COPPER)
14
12
10
8
6
4
2
0
00
000
0000
When measured through the drop cable, the resistance of the drop cablemust be subtracted from the ohmmeter
readings to get the winding resistance of the motor
Reisitance Ohms
MCM WIRE SIZE (COPPER)
0.544
0.338
0.214
0.135
0.082
0.052
0.032
0.021
0.017
0.013
0.010
4MWP
4" Submersible Motors
250
300
350
400
500
600
700
Reisitance Ohms
0.0088
0.0073
0.0063
0.0056
0.0044
0.0037
0.0032
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