Delta Electronics VFD-M User Manual

Page 161

Appendix B Accessories|

B-16

Revision May 2008, ME14, SW V3.04

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:

Use a motor with enhanced insulation.

Connect an output reactor (optional) to the output terminals of the AC motor drive

The length of the cable between AC motor drive and motor should be as short as possible (10

to 20 m or less)

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)

For models 5hp/3.7kW and less:

Insulation level of motor

1000V

1300V

1600V

460VAC input voltage

66 ft (20m)

165 ft (50m)

230VAC input voltage

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. 71

PWM carrier frequency).

Never connect phase lead capacitors or surge absorbers to the output terminals of the AC

motor drive.

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.

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.