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Remember, a DC insulation test may be used for acceptance testing,
but is more commonly used to check the gradual deterioration of
equipment over its life. Consult your equipment manufacturer for spe-
cific test or test voltage if not known.
Insulation resistance decreases with moisture, temperature and age and
should be recorded over time at a given temperature and corrected.
FOR SUCCESSFUL INSULATION RESISTANCE TESTING
•
Check with the equipment manufacturer for factory insulation
resistance readings.
•
Do not rely on insulation resistance testing alone as proof of
winding conditions.
•
Do not expect the same value for all parts of all machines.
•
Observe consistent test time duration, recognizing that total
current through insulation under test will vary with time.
•
Correct all readings properly to a standard reference temperature
(see IEEE Std. #43-1974, Temperature Correction Curve).
•
Know what you are testing. Isolate the piece of equipment from
other circuitry.
•
Watch trends rather than relying on single "spot" readings.
Megohmmeter Models 1020 and 1025
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