GFK-1504K
Chapter 2 Installation Instructions
2-11
2
System Wiring Guidelines
Four types of wiring may be encountered in a typical factory installation:
Power wiring – the plant power distribution, and high power loads such as high
horsepower motors. These circuits may be rated from tens to thousands of KVA at
220 VAC or higher.
Control wiring – usually either low voltage DC or 120 VAC of limited energy rating.
Examples are wiring to start/stop switches, contactor coils, and machine limit
switches. This is generally the interface level of discrete I/O.
Analog wiring – transducer outputs and analog control voltages. This is the interface
level to I/O analog blocks.
Communications and signal wiring – the communications network that ties everything
together, including computer LANs, MAP, and field busses.
These four types of wiring should be separated as much as possible to reduce the hazards
from insulation failure, miswiring, and interaction (noise) between signals. A typical
control system may require some mixing of the latter three types of wiring, particularly in
cramped areas inside motor control centers and on control panels.
In general, it is acceptable to mix the communications bus cable with the I/O wiring from
the blocks, as well as associated control level wiring. All noise pickup is cumulative,
depending on both the spacing between wires, and the distance span they run together. I/O
wires and communications bus cable can be placed randomly in a wiring trough for lengths
of up to 50 feet. If wiring is cord–tied (harnessed), do not include the bus cable in the
harness, since binding wires tightly together increases the coupling and mechanical stress
that can damage the relatively soft insulation of some serial cable types. Consider using
shielded cable in electrically noisy environments.
Wiring which is external to equipment, and in cable trays, should be separated following
National Electrical Code practices.
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