Publication 1764-UM001B-EN-P - April 2002
Understanding Communication Protocols E-9
Hardware Considerations
You need to decide the length of the communication cable, where
you route it, and how to protect it from the environment where it will
be installed.
When the communication cable is installed, you need to know how
many devices are to be connected during installation and how many
devices will be added in the future. The following sections will 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 100 kVA, and 0.60m
(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 0.08m (3 in.)
from ac power lines of less than 20A, 0.15m (6 in.) from lines
greater than 20A, but only up to 100 kVA, and 0.30m (1 ft) from
lines of 100 kVA or more.
Running the communication cable through conduit provides
extra protection from physical damage and electrical
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