Appendix B Accessories_VFD-B Series
B-10 Revision 10/2005, BE13, SW V4.08
The length of motor cable
When motor is driven by an AC motor drive of PWM type, the motor terminals will experience surge voltages
easily due to components conversion of AC motor drive and cable capacitance. When the motor cable is very
long (especially for the 460V series), surge voltages may reduce insulation quality. To prevent this situation,
please follow the rules below:
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Use a motor with enhanced insulation.
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Connect an output reactor (optional) to the output terminals of the AC motor drive
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The length of the cable between AC motor drive and motor should be as short as possible (10 to 20 m
or less)
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For models 7.5hp/5.5kW and above:
Insulation level of motor 1000V 1300V 1600V
460VAC input voltage 66 ft (20m) 328 ft (100m) 1312 ft (400m)
230VAC input voltage 1312 ft (400m) 1312 ft (400m) 1312 ft (400m)
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For models 5hp/3.7kW and less:
Insulation level of motor 1000V 1300V 1600V
460VAC input voltage 66 ft (20m) 165 ft (50m) 165 ft (50m)
230VAC input voltage 328 ft (100m) 328 ft (100m) 328 ft (100m)
NOTE
When a thermal O/L relay protected by motor is used between AC motor drive and motor, it may malfunction
(especially for 460V series), even if the length of motor cable is only 165 ft (50m) or less. To prevent it, please
use AC reactor and/or lower the carrier frequency (Pr. 02-03 PWM carrier frequency).
NOTE
Never connect phase lead capacitors or surge absorbers to the output terminals of the AC motor drive.
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If the length is too long, the stray capacitance between cables will increase and may cause leakage
current. It will activate the protection of over current, increase leakage current or not insure the
correction of current display. The worst case is that AC motor drive may damage.
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If more than one motor is connected to the AC motor drive, the total wiring length is the sum of the
wiring length from AC motor drive to each motor.
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