TM 10-6665-297-13&P
2-6
DETECTOR INSTALLATIONS (continued)
2-6.2
Installing Detector Wiring (continued)
1. When both wire runs are within 20 percent of equal distance, consult Table 2-2 for appropriate wire
gauge, and install same-size wire for both runs. Use of #16 AWG wire is desirable even for very
short runs, and may be used to simplify wire selection where cost of wire is not greatly significant.
2. If the two wire runs are of unequal lengths: First choose wire size from Table 2-2 for the longer run (if
marginal, choose next size larger), then determine exact wire resistance from “OHM-PER-FOOT”
column of Table 2-2. Next, for the second detector, choose a smaller wire gauge from Figure 2-17 to
obtain as nearly as possible the same resistance as the wire for a longer run. (Both sensors must
operate at nearly the same voltage; hence voltage drops in the two wire runs must be nearly equal.
Voltage drop in wires can be computed by determining resistance in ohms for the length and size of
wire, then multiplying by 0.28 amps detector current. Where differences in voltage drops between
leads must be reconciled, set detector operating voltage between the values measured at detectors
for each in accordance with paragraph 2-6.9, step 7.)
3. Signal return wires to terminals C1 and C2 may be #20 AWG or larger for distances to 1100 feet, or
#18 or larger for greater distances.
AWG
Ohms/1000 Ft.
Feet/Ohm
at 68°F
at 68°F
6
.40
2531
8
.63
1593
10
1.0
1000
12
1.6
630
14
2.5
396
16
4.0
249
18
6.4
157
20
10.2
99
Table 2-2. Resistance of Standard Annealed Copper Wire (Values are
approximately, and will vary depending upon resistivity of specific conductor
used.) (See also Resistance Graph, Figure 2-17.)
2-6.2.1 Installing Single Detector on CD800/830 or CD802/832 Control Unit. Install a single detector as
follows (Figures 2-8 through 2-11):
NOTE: Do not disconnect 15-ohm paired resistors factory-installed on DET 2 terminals A, R,
and C.
1.
Connect a green wire between detector active element lead (green, banded “A”) and control
module terminal marked DET 1, A.
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