Introduction
This article applies mainly to hard-wired systems. The components in hard-wired alarm systems are connected together using multi-core cable. The individual cores are colour coded and the cores and a ripcord are enclosed in an outer PVC sheath optionally with a foil screen for use in areas where there is a risk of radio interference. The outer sheath is normally available in white or brown.
Alarm cable is supplied in 4, 6, 8, and 12 core versions.
It is recommended that cable designed for use in alarm systems is used, however, some amateur installers have used CAT5 data cable. The main drawback with CAT5 cable is its power carrying capabilities - the cores may have to be doubled for the power supply to powered detectors.
External Sounders always require 5 cores to connect to the control panel. Hence 6 core cable should be used.
Remote Keypads (RKPs) usually require a maximum of 6 cores to connect to the control panel. Hence 6 core cable shouild be used.
The number of cores required by detectors depends on the type of detector and the wiring scheme used as follows.
Detector Types
From the cabling perspective, there are two classes of detector - non-powered and powered.
All detectors require an alarm loop and a tamper loop, powered detectors such as PIRs, vibration (shock, inertia), and breakglass require 12v power as well. In a conventional Closed Circuit Loop (CCL) installation non-powered detectors will require 4 core cable (2 - alarm loop, 2 - tamper loop) and powered detectors will require 6 core cable (2 - alarm loop, 2 - tamper loop, 2 - 12v +ve & -ve). If Fully Supervised Loop is used then non-powered detectors will require 2 cores (Alarm and Tamper are carried on 2 cores) and powered detectors will require 4 cores (2 extra for 12v +ve & -ve).
Which Cable
Before deciding which cable you will need, we need to explain the two types of detector wiring - Closed Circuit Loop (CCL) or Fully Supervised Loop (FSL) which is also known as End of Line (EOL) or Double Balanced. High-spec control panels have the ability to use either CCL or FSL wiring but not both in the same installation i.e. the whole detection system has to be all CCL or all FSL.
Closed Circuit Loop (CCL)
CCL wiring uses discrete closed loops for the Alarm and Tamper Circuits - 4 cores, and if the detector requires power then an extra 2 cores i.e 6 cores in total. Note that more than 1 detector can be connected into a single closed loop as long as the single closed loops for the aalrm and tamper circuits are preserved. If more than 1 powered detector is connected into the same loop then the connections must be in parallel. See PIR Wiring for details of wiring multiple detectors.
Fully Supervised Loop
FSL wiring uses resistors fitted at the detector to detect the possible alarm conditions as in the following example. Note that the resistance values in the example below are used purely for example; the actual resistor values are dependent on the particular control panel. Detectors are available with the resistors pre-installed, and Control Panels capable of FSL wiring are supplied with resistors of the correct values for the panel.
| Zone resistance (Ohms) |
Condition |
| 0 |
Tamper Short Circuit |
| 10K |
Normal (closed) |
| 33K |
Alarm (open) |
| Infinity |
Tamper Open Circuit |
FSL must be used in Grade 3 and above installations, in conjunction with Grade 3 detectors - i.e. with resistors fitted at the detector and in the case of PIRs those having an anti-mask detection circuit. In normal domestic installations, where there is no public access to the system, there is no need to use FSL wiring, and for the DIY installer it is generally easier and less expensive to use CCL wiring.
Conclusion
Four (4) core cable is used for wiring non-powered detectors in CCL installations and any detector in FSL systems.
Six (6) core cable is used for wiring powered detectors (PIRs etc) in CCL systems, or for wiring two zones of non-powered detectors back to the control panel. Similarly, 6 core cable can be used to carry 2 zones of powered detectors in FSL installations. Six (6) core cable is also used to connect external sounders (SAB/SCB) and Remote Keypads (RKPs) to the control panel.
Eight (8) core cable is used to carry 2 zones of powered detectors in CCL installations or 3 zones of powered detectors in FSL installations.
Twelve (12) core cable is used to carry multiple devices on the same cable back to the control panel.
Screened cable is used where there is a possibility of radio interference - this includes mains-induced spikes, fluorescent lighting, and mobile phones.
|
