Appendix B: Worksheets
P/N 3102351-EN • REV 005 • ISS 28DEC18 203
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 49.
500,000 pF
Cable capacitance ÷ pF/ft.
Total wire ft.
Table 49: Maximum wire length for the loop
type 18 AWG or
0.75 mm²
16 AWG or
1.0 mm²
14 AWG or
1.5 mm²
Twisted pair, nonshielded
20,000 ft.
(6096 m)
13,888 ft.
(4233 m)
13,157 ft.
(4010 m)
8,621 ft.
(2628 m)
6,098 ft.
(1859 m)
5,952 ft.
(1814 m)
Untwisted pair, unshielded
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, UM or
MABs installed on the loop. The distances listed are for devices that are evenly distributed on
the loop. Please contact your distributor for loop wire distances for devices on an end-loaded
loop.
Note: When using the tables to calculate a wire length for the VS1 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).
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