Chapter 7 Optional AccessoriesC2000-HS
7-14
Length of the Motor Cable
1. Leakage current affects the motor and remedies
Due to larger parasitic capacitances in longer motor cables, longer cables increase the leakage
current. This can activate the over-current protection and display the incorrect current. In the worst
case, it can damage the drive.
If more than one motor is connected to the AC motor drive, the total motor cable length is the sum of
the cable length from the AC motor drive to each motor.
For 460V series AC motor drives, when an overload relay is installed between the drive and the motor
to protect the motor from overheating, the connecting cable must be shorter than 50 m.
However, the overload relay could still malfunction. To prevent this, install an AC output reactor
(optional) to the drive and/or lower the carrier frequency setting (Pr. 00-17).
2. Surge voltage affects the motor and remedies
When a PWM signal from an AC motor drive drives the motor, the motor terminals can easily
experience surge voltages (dv/dt) due to IGBT switching and cable capacitance. When the motor
cable is very long (especially for the 460V series), surge voltages (dv/dt) may reduce motor insulation
quality. To prevent this, follow the rules listed below.
a. Use a motor with enhanced insulation.
b. Connect an output reactor (optional) to the output terminals of the AC motor drive.
c. Reduce the motor cable length to the values in the table below.
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