Rockwell Automation 1305 AC Drive, Series A and B, Firmware 4.xx-5.xx - Manual (Page 28)

Chapter 2 – Installation/Wiring
2-12
Motor Cables
A variety of cable types are acceptable for drive installations.
For many installations, unshielded cable is adequate, provided
it can be separated from sensitive circuits. As an approximate
guide, allow a spacing of 1 meter (3.3 feet) for every 10 meters
(33 feet) of length. In all cases, long parallel runs must be
avoided.
The cable should be 4-conductor with the ground lead being
connected directly to the drive ground terminal (GRD) and the
motor frame ground terminal.
Shielded Cable
Shielded cable is recommended if sensitive circuits or devices
are connected or mounted to the machinery driven by the
motor. The shield must be connected to the drive ground and
motor frame ground. The connection must be made at both
ends to minimize the external magnetic field.
If cable trays or large conduits are to be used to distribute the
motor leads for multiple drives, shielded cable is recommended
to reduce or capture the noise from the motor leads and
minimize “cross coupling” of noise between leads of different
drives. The shield should be connected to the ground
connections at both the motor and drive end.
Armored cable also provides effective shielding. Ideally, it
should be grounded only at the drive (GRD) and motor frame.
Some armored cable has a PVC coating over the armor to
prevent incidental contact with grounded structure. If, due to
the type of connector, the armor must be grounded at the
cabinet entrance, shielded cable should be used within the
cabinet to continue as far as possible to the coaxial
arrangement of power cable and ground.
In some hazardous environments it is not permissible to ground
both ends of the cable armor. This is because of the possibility
of high current circulating at the input frequency if the ground
loop is cut by a strong magnetic field. This only applies in the
proximity of powerful electrical machines. In such case, the
ground connection at one end may be made through a
capacitance, which will block the frequency current but present
a low impedance to RF. Because of the highly pulsed nature of
the circulating current, the capacitor type used must be rated
for AC-to-ground voltage. Consult factory for specific
guidelines.