AIM Manual

Motor Maintenance » All Motors (Page 47)

Insulation Resistance Readings

Table 47 Normal ohm and Megohm Values Between All Leads and Ground
CONDITION OF MOTORS AND LEADSMEGOHM VALUEOHMS VALUE
A new motor (without drop cable)
A used motor which can be reinstalled in well
200.0 (or more)
10.0 (or more)
200,000,000 (or more)
10,000,000 (or more)
MOTOR IN WELL. READINGS ARE FOR DROP CABLE PLUS MOTOR.2.0 (or more)
0.50 - 2.0
Less than .50
2,000,000 (or more)
500,000 - 2,000,000
Less than 500,000
New motor

Motor in good condition

Insulation damage, locate and repair
MOTOR IN WELL. READINGS ARE FOR DROP CABLE PLUS MOTOR.MEGOHM VALUEOHMS VALUE
New motor

Motor in good condition

Insulation damage, locate and repair
2.0 (or more)
0.50 - 2.0
Less than .50
2,000,000 (or more)
500,000 - 2,000,000
Less than 500,000
  • 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.

Resistance of Drop Cable (ohms)

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, 25, & 27. 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.

Table 47A DC Resistance in ohms per 100 ft of Wire (Two conductors) @ 50 °F
AWG OR MCM WIRE SIZE (COPPER)14121086432
OHMS0.5440.3380.2140.1350.0820.0520.0410.032
11/02/03/04/0250300350400500600700
0.0260.0210.0170.0130.010.00880.00730.00630.00560.00440.00370.0032