Download York YR Technical data

160.81-ICOM-GB0 (01/02)
7.9
Testing Motor Winding Insulation
With the main disconnect switch and compressor motor
starter open, test the motor as follows:
1.
Test the insulation, using a megohm meter
(megger), between phases and each phase and
ground as shown; these readings are to be
interpreted using the graph shown in below.
2.
If readings fall below shaded area, remove external
leads from motor and repeat test.
7- 9
Motor is to be megged with the starter at
ambient temperature after 24 hours of idle
standby.
Minimum Insulation Resistance vs. Temperature (per IEEE Std 43)
48.9°C
43.3°C
°C
37.8°C
32.2°C
26.7°C
21.1°C
15.6°C
10.0°C
4.4°C
1. Megohm readings should be taken after Megohm voltage has been applied one minute.
2. If insulation resistance lies to the right of the applicable curve, the motor is acceptable for
use.
3. If insulation resistance lies to the left of the applicable curve, the motor should not be run.
The motor should be heated to 250°F in an effort to remove moisture and obtain an
acceptable reading at room ambient.This can be done either by baking in a forced hot air
oven or, if proper voltage is available, apply 5 - 10% of rated voltage to motor windings.
4. Any gradual or abrupt decrease in Megohm readings over an extended period of time is
an indication of deterioration of insulation and/or moisture absorption or oil/dirt
contamination.
5. Megohm readings of individual phase coils of 200 - 600V motors should be made with
coils not under test being grounded.