Rockwell Automation 5000,D50006.2.10 PI INSTALLATION MANUAL User Manual
Page 106
Chapter 7
Installing 1771 I/O
7-18
Unless otherwise specified, connect each cable shield to earth ground at the
I/O-chassis end as we describe here. Always connect the shield to ground
at one end of the cable only (never ground any cable shield at both ends).
A shield grounded at both ends forms a ground loop which could cause
faulty operation.
Ground each shield at the end specified in the appropriate publication for
the product. Never connect a shield to the common side of a logic circuit
(this would introduce noise into the logic circuit). Connect each shield
directly to a chassis ground.
Since each I/O chassis must be connected to earth ground, any connection
to a properly mounted I/O chassis is also a connection to ground.
To properly connect a shielded cable at a wiring arm and connect the shield
to ground at the I/O chassis, execute the following procedure:
1. At the cable end which is to connect to the wiring arm, strip off 3 ft
of the outer jacket to expose the foil.
2. Strip off the exposed foil. It may be necessary to insulate the bare
drain wire with tape or shrink- tubing along areas where it might
otherwise come into contact with wiring arm terminals.
3. Trim both insulated wires to 2-inch lengths. Then strip
approximately 3/8-inch of insulation from the end of each wire. The
shield strand (drain wire) is left at its full 3-ft length (Figure 7.11).
Figure 7.11
Shielded Wire Striped and Ready for Installation
3 ft
Twinaxial cable
2"
3/8"
Blue
Clear
Drain wire
18007
4. Connect the insulated wires at the wiring arm terminals specified in
the I/O module product data publication. Fold back the bare drain
wire as you route the cable. The insulated wires connect to the user
device at the other end of the cable.
5. Connect the bare drain wire to ground. Route it from the wiring arm
to the I/O chassis stud or an I/O chassis ground bus. A lug can be
used. In applications where many shielded cables are connected at a
single I/O chassis it may be necessary to mount a ground bus directly
below the I/O chassis for a ground connection for these drain wires as
in