Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 76)

Publication GMC-RM001A-EN-P — July 2001
8-4 Motor Wiring
Handling Excess Cable Observe the following guidelines when handling excess cable:
• Do not coil excess cable of different types (i.e. motor power and
feedback) together. An efficient transformer is formed at HF.
• Cable lengths should ideally be trimmed to fit the application.
• If excess cable cannot be trimmed, it should be laid in an 'S' or
figure eight pattern (refer to the figure below).
Figure 8.4
Excess cable treatment
Installing Long Motor
Cables Motor cables are defined as long when the motor frame is not bonded
close enough to the drive panel to be considered a single ground
plane. To be considered a single ground plane, the parts must be
connected by a surface which is no longer than ten times its width.
Refer to the chapter High Frequency (HF) Bonding for methods of
achieving a single ground plane.
Observe the following guidelines when installing long motor cables:
• Bonding should be by the widest practical means. Wide cable tray
is effective when it is made of zinc plated steel and carefully
bonded at the ends to control panel and motor frame.
• Zinc plated sheet steel channel is also effective. The fact that the
width is folded into a U shape does not matter. A closing lid helps.
• Solid steel conduit bonded at both ends is effective.
• The spiral construction of flexible conduit makes it less attractive
for RF shielding because the spiral shape forms an inductor, even
with partially shorted turns.
Preferred Methods
Poor Method