Appendix B: Worksheets
206 Vigilant VS1 and VS2 Technical Reference Manual
Notes
[1] Use the manufacturer’s published wire resistance expressed in ohms per foot. For typical values,
see Table 43 on page 202.
[2] Use the Maximum operating current at worst-case VFWR from the installation or catalog sheet of
each device.
[3] For UL regulated notification appliances, this voltage must not drop below 16 VFWR. For other
devices, get the minimum operating VFWR from the installation or catalog sheet.
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 46.
700,000 pF
Cable capacitance pF/ft.
Total wire ft.
Table 46: Maximum wire length for the loop
Wire type 18 AWG or
0.75 mm²
16 AWG or
1.0 mm²
14 AWG or
1.5 mm²
Twisted pair, nonshielded
25, 36, 38 pF
20,000 ft.
(6096 m)
13,888 ft.
(4233 m)
13,157 ft.
(4010 m)
Twisted pair, shielded
58, 82, 84 pF
8,621 ft.
(2628 m)
6,098 ft.
(1859 m)
5,952 ft.
(1814 m)
Untwisted pair, unshielded
20, 20, 20 pF
20,000 ft.
(6096 m)
20,000 ft.
(6096 m)
20,000 ft.
(6096 m)
Step 2: Longest path
Use the tables that follow 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-UM or -MABs installed on the loop. The distances listed are for devices
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