Rockwell Automation 1762-Lxxxx MicroLogix 1200 Programmable Controllers - Manual (Page 137)

Publication 1762-UM001G-EN-P - March 2011
Connect to Networks via RS-232 Interface E-7
Number of Devices and Length of Communication Cable
The maximum length of the communication cable is 1219 m (4000 ft). This is
the total cable distance from the first node to the last node in a segment.
However, two segments can be used to extend the DH-485 network to 2438 m
(8000 ft). For additional information on connections using the AIC+, refer to
the Advanced Interface Converter (AIC+) User Manual, publication
1761-UM004.
Planning Cable Routes
Follow these guidelines to help protect the communication cable from
electrical interference:
• Keep the communication cable at least 1.52 m (5 ft) from any electric
motors, transformers, rectifiers, generators, arc welders, induction
furnaces, or sources of microwave radiation.
• If you must run the cable across power feed lines, run the cable at right
angles to the lines.
• If you do not run the cable through a contiguous metallic wireway or
conduit, keep the communication cable at least
0.15 m (6 in.) from ac power lines of less than 20 A, 0.30 m (1 ft) from
lines greater than 20 A, but only up to 100 kVA, and 0.60 m (2 ft) from
lines of 100 kVA or more.
• If you run the cable through a contiguous metallic wireway or conduit,
keep the communication cable at least 0.08 m (3 in) from ac power lines
of less than 20 A, 0.15 m (6 in) from lines greater than 20 A, but only up
to 100 kVA, and 0.30 m (1 ft) from lines of 100 kVA or more.
Running the communication cable through conduit provides extra
protection from physical damage and electrical interference. If you route
the cable through conduit, follow these additional recommendations:
– Use ferromagnetic conduit near critical sources of electrical
interference. You can use aluminum conduit in non-critical areas.
– Use plastic connectors to couple between aluminum and
ferromagnetic conduit. Make an electrical connection around the
plastic connector (use pipe clamps and the heavy gauge wire or wire
braid) to hold both sections at the same potential.
– Ground the entire length of conduit by attaching it to the building
earth ground.
– Do not let the conduit touch the plug on the cable.
– Arrange the cables loosely within the conduit. The conduit should
contain only serial communication cables.