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If the readings on a field-installed starter are unsatisfactory, repeat the test at the motor with
the power leads disconnected. Satisfactory readings in this second test indicate the fault is
in the power leads.
Note: Unit-mounted starters do not have to be megohm tested.
Check Insulation Resistance (Open-Drive Motor)
Before operating voltages is applied to the motor, whether for checking rotation direction or
for actual operation, the resistance of the stator winding insulation should be measured.
The test voltage, based on the motor operating voltage, is as follows:
This is particularly important if the motor may have been exposed to excessive dampness
either during transit or while in storage. A ‘‘megger’’ type instrument can be used to measure
the insulation resistance. The test voltage should be applied between the entire winding (all
winding leads connected together) and ground for approximately one minute with the winding at
ambient temperature. The recommended minimum insulation resistance is determined as
follows:
Operating Voltage DC Test Voltage
0- 900 500
901- 7000 1000
7001-14500 2500