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Maintenance – All Motors
Insulation Resistance Readings
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.
Winding Resistance Measuring
The winding resistance measured at the motor should
fall within the values in tables 13, 22, 24 & 26. When
measured through the drop cable, the resistance of
the drop cable must be subtracted from the Ohmmeter
readings to get the winding resistance of the motor. See
table below.
Insulation resistance varies very little with rating. Motors of all hp, voltage, and phase rating have similar values of
insulation resistance.
The table above is based on readings taken with a megohm meter with a 500 VDC output. Readings may vary using a lower
voltage Ohmmeter, consult Franklin Electric if readings are in question.
Table 45 Normal ohm and Megohm Values Between All Leads and Ground
Table 45A DC Resistance in ohms per 100 ft of Wire (Two conductors) @ 50 °F
CONDITION OF MOTOR AND LEADS OHMS VALUE MEGOHM VALUE
A new motor (without drop cable).
A used motor which can be reinstalled in well.
200,000,000 (or more)
10,000,000 (or more)
200.0 (or more)
10.0 (or more)
MOTOR IN WELL. READINGS ARE FOR DROP CABLE PLUS MOTOR.
2,000,000 (or more)
500,000 - 2,000,000
Less than 500,000
2.0 (or more)
0.50 - 2.0
Less than .50
New motor.
Motor in good condition.
Insulation damage, locate and repair.
AWG OR MCM WIRE SIZE (COPPER) 14 12 10 86432
OHMS
0.544 0.338 0.214 0.135 0.082 0.052 0.041 0.032
1 1/0 2/0 3/0 4/0 250 300 350 400 500 600 700
0.026 0.021 0.017 0.013 0.010 0.0088 0.0073 0.0063 0.0056 0.0044 0.0037 0.0032
Resistance of Drop Cable (ohms)
45