Rockwell Automation 1336T Wiring and Grounding Guide, (PWM) AC Drives - Manual (Page 20)

20 Rockwell Automation Publication DRIVES-IN001M-EN-P - March 2014
Chapter 1 Wire/Cable Types
Motor Cables The majority of recommendations regarding drive cables are for issues caused by
the nature of the drive output. A PWM drive creates AC motor current by
sending DC voltage pulses to the motor in a specific pattern. These pulses affect
the wire insulation and can be a source of electrical noise. Consider the rise time,
amplitude, and frequency of these pulses when choosing a wire/cable type.
Consider these factors when choosing a cable:
• The effects of the drive output once the cable is installed.
• The need for the cable to contain noise caused by the drive output.
• The amount of cable charging current available from the drive.
• Possible voltage drop (and subsequent loss of torque) for long wire runs.
Keep the motor cable lengths within the limits set in the user manual for the
drive. Various issues, including cable charging current and reflected wave voltage
stress, can exist. If the cable restriction is listed because of excessive coupling
current, apply the methods to calculate total cable length, as shown in
Figure 11 .
If the restriction is due to voltage reflection and motor protection, refer to
Appendix A for exact distances allowed.
Figure 11 - Motor Cable Length for Capacitive Coupling
182.9 (600)
91.4 (300) 91.4 (300)
15.2 (50)
167.6 (550) 152.4 (500)
15.2 (50) 15.2 (50)
All examples represent motor cable length of 182.9 m (600 ft)
IMPORTANT For multi-motor applications, review the installation carefully. Consult your
distributor drive specialist or Rockwell Automation when considering a
multi-motor application with greater than two motors. In general, most
installations have no issues. However, high peak cable charging currents can
cause drive over-currents or ground faults.