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Check Insulation Resistance (Hermetic Motor)
Test the machine compressor motor and its power lead insulation resistance with a 500-v
insulation tester such as a megohmmeter. (Use a 5000-v tester for motors rated over 600 v.)
Factory-mounted starters do not require a megohm test.
1.
Open the starter main disconnect switch and follow lockout/tagout rules.
2.
With the tester connected to the motor leads, take 10-second and 60-second megohm
readings as follows:
6-Lead Motor
— Tie all 6 leads together and test between the lead group and ground. Next
tie leads in pairs, 1 and 4, 2 and 5, and 3 and 6. Test between each pair while grounding the
third pair.
3-Lead Motor — Tie terminals 1, 2, and 3 together and test between the group and ground.
3.
Divide the 60-second resistance reading by the 10-second reading. The ratio, or
polarization index, must be one or higher. Both the 10- and 60-second readings must be at
least 50 megohms.
CAUTION
CAUTION
!
If the motor starter is a solid-state starter, the motor leads must be disconnected
from the starter before an insulation test is performed. The voltage generated
from the tester can damage the starter solid-state components.