Allen-Bradley MicroLogix 1200 User Manual page 129

devices will be added in the future. The following sections help you
understand and plan the network.
Number of Devices and Length of Communication Cable
The maximum length of the communication cable is 1219m (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 2438m (8000 ft). For additional information on
connections using the AIC+, refer to the Advanced Interface Converter
(AIC+) User Manual, publication 1761-6.4.
Planning Cable Routes
Follow these guidelines to help protect the communication cable from
electrical interference:
• Keep the communication cable at least 1.52m (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
0.15m (6 in.) from ac power lines of less than 20A, 0.30m (1 ft)
from lines greater than 20A, but only up to 100K VA, and 0.60m
(2 ft) from lines of 100K VA or more.
• If you run the cable through a contiguous metallic wireway or
conduit, keep the communication cable at least 0.08m (3 in.)
from ac power lines of less than 20A, 0.15m (6 in.) from lines
greater than 20A, but only up to 100K VA, and 0.30m (1 ft) from
lines of 100K VA 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.
Connecting to Networks via RS-232 Interface
Publication 1762-UM001D-EN-P - March 2004
E-7