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e-PAQ-9150
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1.6.4 External Wiring
The following paragraphs provide information on connecting external transducers,
communication lines, and power to the Remote Terminal Unit.
Do not use unnecessarily large-sized wire for status, analog, and control lines. The larger wires do not
provide any extra safety factor and can clutter the cabinet to the detriment of both installation and
maintenance personnel.
Status Inputs
Since small (typically 4-milliampere) currents are carried, the wire size is not critical,
#22 AWG will provide adequate capacity. Each status input requires two wires from
the status point. Shielded twisted pairs are recommended, but this is not mandatory.
Analog Inputs
Analog inputs generally carry 20 mA or less, and #22 AWG wire is adequate. Use a
shielded twisted pair for each analog point. Connect the shield to earth ground at the
transducer end only.
Control Outputs
Control lines may be straight or twisted pairs, with sufficient current carrying capacity
for the controlled device. Although the relay panel contacts may be rated for several
amperes, it is not necessary for the wire to meet this capacity if the controlled device
does not require it.
Communication Lines
Communication lines are either via RS-232 or RS-485. Regular RS-232 cables
adhering to the CCITT standard are adequate and for RS-485, twisted pairs with a
common shield may be used. Observe proper grounding practices for signals of
either type.
If the optional Ethernet interface is utilized then industry standard CAT-5 cables are
required for proper operation.
If the optional 202T modems are utilized, then the communication lines are either
two-wire or four-wire. Regular telephone wire should be used for systems
interconnected via telephone-company lines. For self-contained systems, separate
twisted pairs with individual shields may be used for each line.
16
Section 1
NOTE
Remote Terminal Unit
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