Rockwell Automation SA3100 AC Power Modules - Manual (Page 39)

Installation Guidelines 3-21
If cable trays or large conduits are used to distribute the motor leads for multiple
drives, shielded cable is recommended to reduce cross-coupling of noise between the
leads of different drives. The shields should be connected to the ground connections
at both the motor and drive ends.
Armored cable may also provide effective shielding. Ideally, armored cable should be
grounded only at the Power Module (PE) and motor frame. Armored cable having a
PVC coating over the armor to prevent incidental contact with a grounded structure is
recommended. If the armor is grounded at the cabinet entrance, shielded cable
should be used within the cabinet if power leads will be run close to control signal
leads.
In some environments, such as the proximity of very high current electrical machines,
it may not be not permissible to ground both ends of the cable shield. In these
environments the presence of strong magnetic fields may induce high currents in the
ground loop formed by the shield or cable armor and earth grounds. In such cases,
consult with the factory for specific guidelines.
3.13.2 Guidelines for Using Conduit
If metal conduit is preferred for cable distribution, the following guidelines should be
observed:
1. Power Modules are normally mounted in cabinets, and ground connections are
made at a common ground point in the cabinet. Installation of conduit should
provide grounded connections to both the motor frame ground (junction box) and
the Power Module cabinet ground to help minimize electrical interference. These
connections are for noise reduction only, and do not meet the requirements for
safety grounding (section
3.14.1).
2. The number of motor leads per conduit must be minimized to reduce cross-talk.
No more than one set of unshielded motor leads should be routed through a
single conduit. If more than one set of motor leads per conduit is required,
shielded cable must be used.
3.13.3 Maximum Motor Lead Lengths
Installations with long motor cables may require the addition of an output reactor,
common mode filter, or terminator to limit voltage reflections at the motor. Refer to
table D.1 in Appendix D for the maximum length of motor cable allowed for various
installation techniques. For installations that exceed the recommended maximum
lengths listed contact the factory.
!
ATTENTION:To avoid a possible shock hazard caused by induced
voltages, unused wires in the conduit must be grounded at both ends. If
a Power Module sharing a conduit is being serviced or installed, all Power
Modules using this conduit must be disabled to eliminate the possible
shock hazard from cross-coupled motor leads.