Rockwell Automation SA3100 AC Power Modules - Manual (Page 103)

Motor Cables D-1
A
PPENDIX
D
Motor Cables
A variety of cable types are acceptable for SA3100 Power Module installations. For
many installations, using separate conductors or unshielded cable is adequate. Signal
wire for sensitive circuits must be run in separate conduit and be physically separated
from inverter output cables. As an approximate guide, allow a minimum separation of
0.3 meters (1.0 ft) between cable types.
Motor cable should be 3-conductor with ground. The motor cables should run in the
same wire raceway. The ground leads should be connected directly to the Power
Module ground terminal (PE) and to the motor frame ground terminal.
Shielded Cable
Shielded cable, as referred to in this manual, is defined as any multi-conductor cable,
with or without a ground conductor, that has a conductive metallic jacket surrounding
the power conductors. The shield may be steel, aluminum, or copper, and may be
continuous or spiral wrapped. The shield may provide physical protection for the
cables, or may only provide a barrier to electrical fields, electrostatic or
electromagnetic.
Shielded cable is recommended to help avoid interference with any sensitive circuits
or devices that are present. The shield must be connected to the Power Module
ground terminal (PE) and to the motor frame ground terminal.
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 shield should be connected to the ground (PE)
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. 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 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. If the ground
loop formed by the cable shield is cut by a strong magnetic field, a high circulating
current may be produced. In this case, the ground connection at one end may be
made through a capacitance. The capacitance will block the low frequency circulating
current but present a low impedance to RFI. Because of the highly pulsed nature of
the inverter output voltage, the capacitor type used must be rated for AC. Consult the
factory for specific guidelines.