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 concentrators. These units can also be used for local (area) reporting
within the distributed IDS network. Communication wiring for these units
requires sensor wiring usually two pair (or less) of unshielded direct
current low-voltage cable or of shielded data communication pairs. The
gauge and length of wiring specification is dependent upon system specific
needs, often a limitation of wire resistance. Table 17 lists possible gauge
and line lengths to maintain 30 ohms or less of resistance, normal parameter
for an IDS line. The data communications line length and gauge is likely to
be specified by the manufacturer for performance at a site specific
installation. Care
Table 17
Typical Alarm Loop Lengths
Wire
Resistance (ohms)
Maximum Loop
Gauge
Per Kilo Foot
Per 30 ohms
(AWG)
22
16.704
1795 ft
20
10.35
2809 ft
18
6.51
4608 ft
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