Spectrex 40/40M Multi IR Flame Detector - Manual (Page 62)

Multi IR Hydrocarbon and Hydrogen Flame Detector User Guide
50 General Instructions for Electrical Wiring
Table 26: Wiring length in feet (meter)
Number
of
Detectors
Recommended Wire Diameter (AWG)
Power
Supply
Range
(VDC)
24 18 16 14 - - 22-32
20 18 16 14 - - 22-32
16 20 18 16 14 - 22-32
12 20 18 16 14 - 20-32
8 20 18 16 14 - 20-32
4 and less 20 18 16 16 14 20-32
Ft (m) 164
(50)
328
(100)
492
(150)
656
(200)
820
(240)
Max. Length from Power Supply to Last
Detector
Calculation Formula
Use the following formula to calculate minimum wire gauge per wire length
between the power supply (controller) and the detector, considering the
number of detectors on the same power line, where:
L = Actual wire length between the detector and the power supply.
N = Number of detectors per loop.
R = Resistance of wire per 100 m (see Table 26).
V = Voltage drop on the wire.
Calculate the voltage drop on the wire as follows:
V = 2L x R x N x 0.2A
100
20+V = Minimum required voltage of the power supply
0.2A is the maximum power consumption of the detector
For example,
If N=1 (1 detector in loop)
L=1000m
Wire size = 1.5mm² (see Table 25, the resistance per 100m for 1.5mm² is
1.4Ω)
You calculate the voltage drop in the wire as follows:
2 x 1000 x 1.4Ω x 1 x 0.2A = 5.6V
100
The minimum voltage of the power supply should be 20V + 5.6V = 25.6V