Rockwell Automation 8520 9/Series CNC Integration Maintenance Manual Documentation Set - Manual (Page 421)

Section 7C
Power Distribution and Wiring Guidlines
7C-3
Figure 7C.1
Shielded Twisted-pair Cables
Signal source Signal destination
Connect the cable shielding
through a terminal block
DO NOT connect the
cable shielding to
ground at the
signal destination
Differential input
PE
A
B
C
C A C C A
C
B
B
B
Twisted pair
Cable shielding
Exposure of the
signal cables
must be minimal
11237-I
When parallel wires are used for carrying control signals, if distances
between the noise source and the individual cables differs, one of these two
wires will be subject to stronger radiation noise than the other. However,
when a twisted--pair cable is used, both wires will be subject to equal
radiation noise regardless of the position of the noise source. This means
that equal noise voltage is applied to both of the differential input
terminals. Thus, the noise applied to the two terminals will cancel each
other and reduce the drive circuit noise.
Usually, twisted-pair shielded cables as illustrated in Figure 7C.1 are used
to transmit weak signals such as drive signals and feedback signals.
Separation of Cable Routes
Route cables with high power and low power levels (voltages and/or
currents) separately. Run cables along opposite sides of the cabinet to
minimize the influence of magnetic and electromagnetic induction noises.
Install steel sheet metal wireways between machine application cabinets.
Do not use aluminum or other non-ferrous wireways as they do not provide
magnetic shielding for the cables. Do not use dissimilar metals as this may
lead to noise buildup. In wireways, bundle wires loosely into groups
according to similar power levels and functions.
Do not run cables carrying weak signals such as drive signals and feedback
signals in parallel with the ac power cables and I/O cables. If they must be
run in parallel with each other, pass the weak signal carrying cables in
metallic conduit to protect them from the influence of magnetic and