Rockwell Automation 1770 DH,DHII,DH485 CABLE - Manual (Page 30)

Planning a Data Highway or Data Highway Plus
Cable System
Chapter 2
2-14
The I/O raceway layout of a system is reflective of where the different
types of I/O modules are placed in an I/O chassis. Therefore, you should
determine I/O module placement prior to any layout and routing of wires.
However, when planning your I/O module placement, segregate the
modules based upon the conductor categories published for each I/O
module so that you can follow these guidelines. These guidelines coincide
with the guidelines for “the installation of electrical equipment to minimize
electrical noise inputs to controllers from external sources” in IEEE
standard 518-1982.
Categorize Conductors
Segregate all wires and cables into the three categories shown in
Table 2.B. Refer to the publication for each I/O module for the conductor
category classification of each I/O line.
Table 2.B
Follow these guidelines for grouping conductors
Group conductor cables fitting this description: Into this
category:
Examples:
Control & ac Power - highĆpower conductors that are more
tolerant of electrical noise than category 2 conductors and
may also cause more noise to be picked up by adjacent
conductors.
• corresponds to NEC articleĆ725 class 1
• corresponds to IEEE levels 3 (low susceptibility) &
4 (power)
Category 1 • ac power lines
• highĆpower digital ac I/O lines - to connect ac I/O
modules rated for high power and high noise
immunity.
• highĆpower digital dc I/O lines - to connect dc I/O
modules rated for high power or with input circuits
with long timeĆconstant filters for high noise rejection.
They typically connect devices such as hardĆcontact
switches, relays, and solenoids.
Signal & Communication - lowĆpower conductors that are
less tolerant of electrical noise than category 1 conductors
and should also cause less noise to be picked up by
adjacent conductors (they connect to sensors and
actuators relatively close to the I/O modules).
• corresponds to NEC articleĆ725 classes 2 & 3
• corresponds to IEEE levels 1 (high susceptibility) &
2 (medium susceptibility)
Category 2 • analog I/O lines and dc power lines for analog
circuits
• lowĆpower digital ac/dc I/O lines - to connect to I/O
modules that are rated for low power such as
lowĆpower contactĆoutput modules.
• lowĆpower digital dc I/O lines - to connect dc I/O
modules that are rated for low power and have input
circuits with short timeĆconstant filters to detect short
pulses. They typically connect to devices such as
proximity switches, photoĆelectric sensors, TTL
devices, and encoders.
• communication cables (remote I/O, extendedĆlocal
I/O, DH+  , DHĆ485, RSĆ232ĆC, RSĆ422, RSĆ423
cables) - to connect between processors or to I/O
adapter modules, programming terminals,
computers, or data terminals.
I/O Raceway Layout
Considerations