16
Safety and Technical Manual
Rev: 2
Form No. F_020521
VSF303 Flame Detector
This document is strictly private and confidential, reproduction without Viking Corporation approval is prohibited. © 2021 The Viking Group Inc.
4 System Design Guidelines
The following guidelines are intended to assist with the electrical design and engineering of systems
where it is intended that flame detectors will be used.
Power Supply
The detector requires an absolute minimum supply voltage of 18Vdc, as measured at the detector
terminals. The system power supply voltage and power distribution should be arranged such that on
the longest cable run the detector(s) has a supply voltage of greater than 18Vdc.
Cable Selection
Cable to be used for installation is to be selected with a temperature rating of greater than 77 °F
(25 °C) above the maximum ambient temperature.
The metric cable entries are fitted with an internal stop. This internal stop has an IP washer
mounted directly above it. Ensure this is fitted to maintain the ingress protection. This will result in
threads of the cable gland being visible. Do not over tighten.
The installation and local regulations and standards determine the overall cable specification. This
section specifies suitable cable characteristics to ensure correct operation of the flame detector.
DC Power
NOTE: Table 2 shows an absolute maximum for cable length; try not to approach this value.
DO NOT ground any cable shields at the detector housing.
Table 2: Maximum Cable Lengths (24Vdc supply)
Installation
based on 24V
nominal supply
Number of
Flame
Detectors
Maximum
Power (W)
Maximum Cable
Length (m) with
1.5mm2
Conductors
(12Ω/km)
Maximum Cable
Length (m)with
2.5mm2
Conductors
(7.6Ω/km)
Heater on
1
12W @ 24Vdc
500
780
Heater off
1
3W @ 24Vdc
2000
3000
Table 3: AWG Conversions
Cross Sectional Area (mm
2
) American Wire Gauge
(AWG)
Typical Conductor Resistance
per km (3280 ft.)
DC Ω/km @ 20°C
(Approx.)
0.5
22
36
1.0
18
19
1.5
16
12
2.5
14
7.6
