16
6-1) Measurement of insulation resistance
•
When measuring the insulation resistance, disconnect the motor from the control panel.
Measure the insulation resistance before connecting to power source. The insulation resistance (R) varies according to
the motor output, voltage, type of insulation, coil temperature, humidity, dirt, period of operation, test duration, etc.
Insulation resistance should exceed the values shown in Table 14 in most cases.
Table 14 Insulation resistance
6-2) Protection coordination
(1) Use a molded case circuit breaker for circuit protection.
(2) Use an overload protection device that protects the unit when an electric current exceeding that shown on the
rating plate flows.
(3) Use an overload protector which protects the unit within the rated locked time by allowable locked rotor current
indicated in the nameplate for explosion-proof type motors .
Motor voltage
500V
1000V
1M or more
5M or more
R
+ 0.5 (M
)
R
(M )
Low-voltage motor of 600V or less
High-voltage motor of 3000V or more
Reference: The following equations are shown in JEC - 2100.
Rated Voltage (V)
Rated Output (kW) + 1000
Rated Output (kW) + 2000
A drop in insulation resistance may be attributed to poor insulation. In that case, do not turn on the power. Contact our
nearest agent, distributor, or sales office.
Rated Voltage (V) + Speed (r/min)/3
Megohmmeter voltage Insulation resistance (R)
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