JOHNSON CONTROLS
29
SECTION 6 - MAINTENANCE
FORM 160.76-O1
ISSUE DATE: 6/15/2015
6
LD00476
FIGURE 15 -
MOTOR STARTER TEMPERATURE AND INSULATION RESISTANCES
TEMPERATURE – °F
MEGOHMS
Minimum Insulation Resistance vs. T
emperature (per IEEE Std 43)
Open Motors
1. Megger readings should be taken after Megger 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 Megger readings over an extended period of time is an indication of
deterioration of insulation and / or moisture absorption or oil / dirt contamination.
5.
Megger readings of individual phase coils of 200 - 600V motors should be made with coils not under
test being grounded.
LEGEND
A
200 - 600V
DEL
TA
CONN.
B
2300V
(Entire W
indings)
C
200 - 600V
(Per Phase)
Note 5
D
3300 - 4160V
(Entire W
indings)
