Appendix B: Worksheets
Vigilant VS1 and VS2 Technical Reference Manual
219
Device loop maximum wire length worksheet
Use the instructions provided below to calculate the maximum wire
length for a device loop. The maximum wire length is made up of
two components: the total amount of wire and the longest circuit
path.
Step 1: Total wire
Use the worksheet below to calculate the total amount of wire that
you can use to construct a device loop. The total amount of wire is
based on the cable manufacturer's capacitance per foot rating. In
no case shall the total amount of wire exceed the values listed in
Table 1.
500,000
pF
Cable capacitance
÷
pF/ft.
Total wire
ft.
Table 1: Maximum amount of wire you can use to construct an intelligent
addressable loop
Wire type
18 AWG or
0.75 sq mm
16 AWG or
1.0 sq mm
14 AWG or
1.5 sq mm
Twisted pair, nonshielded
25 pF/36 pF/38 pF
20,000 ft.
(6096 m)
13,888 ft.
(4233 m)
13,157 ft.
(4010 m)
Twisted pair, shielded
58 pF/82 pF/84 pF
8,621 ft.
(2628 m)
6,098 ft.
(1859 m)
5,952 ft.
(1814 m)
Nontwisted pair, nonshielded
20 pF/20 pF/20 pF
20,000 ft.
(6096 m)
20,000 ft.
(6096 m)
20,000 ft.
(6096 m)
Step 2: Longest path
Use Table 2 through Table 5 to determine the device loop’s longest
circuit path. The longest circuit path is based on wire size and type,
and the number of detectors, modules, GSA–UMs or GSA–MABs
installed on the loop. The distances are listed as worst case with the
end loop loaded.
Note:
When using Table 2 through Table 5 to calculate a wire length
for the 64 point panel, do not exceed a total of 64 device addresses
(any combination of detectors and modules).
In the illustration below, the longest circuit path (shown in bold lines)
is 1,240 ft. (378 m). The total amount of wire comprising the loop is
1,640 ft. (500 m)
