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6-2) Measurement of insulation resistance
· Always cut off the connection with control board when measuring the insulation resistance for motor. Motor resistance
must be measured independently.
Measure the insulation resistance before wiring. Insulation resistance (R) varies by the effect of: Motor output, voltage, type
of insulation, coil temperature, humidity, dirt, period of operation, loading duration during test, etc. Minimum value necessary
is shown in Table 5.
Motor voltage
Megohmmeter voltage
Insulation resistance (R)
Low-voltage motor of 600V or less
500V
1M (
Ω
) or more
High-voltage motor of 3000V or more
1000V
5M (
Ω
) or more
Table 5 Insulation resistance
Reference: The following equations are shown in JEC-2100.
R > or =
Rated voltage (V)
Rated output (kW) + 1000
(M
Ω
)
R > or =
Rated voltage (V) + Speed (r/min)/3
Rated output (kW) + 2000
+0.5 (M
Ω
)
Do not turn the power on when insulation resistance is low. Contact our agent, distributor, or sales office immediately. It may
be an insulation failure caused by some reason.
6-3) Coordination of System Protection
(1) Use a molded case circuit breaker for protection from short-circuiting.
(2) Use an overload protection device. The device should function when the current exceeds rated current value shown on
the nameplate.
(3) Use an overload protection device with higher level for
explosion-proof type motor
. The device should lock within
allowable locking time at locking current value shown on the nameplate.
