Electrical Contracting News (ECN) October 2016 - Page 44

FIRE SAFETY SYSTEMS IT TAKES TWO Time is money. With budget constraints the norm, system installers and electrical contractors are well aware of the cost benefits and labour saving benefits from cabling simplification. The streamlined setting of front-of-panel system configurations, too, makes on site installations quicker. Here Jonathan Gilbert of Kentec Electronics explains how developments in two wire alarm systems offer a timely solution. I t’s a fact that rethinking cable management can reduce installation costs and speed system set up by simplifying connectivity. Most conventional fire systems are designed to work with two pairs of wires per zone: one pair for detection devices such as smoke detectors, heat detectors and manual call points; the other for alarm devices such as bells, sounders or strobes. By using different line parameters for silent and alarm states, two wire systems support both detection and alarm device components on the same pair of cables. When powered and controlled by the two wire fire panel, this reliable technology takes all the complexity out of fire alarm system design, leading to quicker, less expensive and more flexible installation. Indeed, research shows that a two wire system can achieve a 20-25 per cent labour reduction compared with a standard four wire conventional system. The two wire concept has been developed to make the design and installation of a fire detection and alarm system easier and more economic for small to medium sized buildings, compared with standard four wire conventional systems. The range also allows an existing system to be extended or modified if necessary. These two wire layouts correspond to designated detection zones, which cover the necessary areas of the protected property, with the system’s supporting fire alarm control panel indicating the zone identified when an alarm condition is detected. More flexible and less expensive to install than four wire systems, the two wire concept is cost efficient arising from the system’s simple mode of wiring detectors, call points and sounders to the same pair of fire protected cables that carries both the initiating circuit and power, hence eliminating the need to install sounder circuit cables at added cost. There can be no doubt that the two wire approach for smaller installations is far less costly than for an addressable system. Having sounders and sounder beacons installed on the detection circuits, with the same cabling as detectors and call points, allows the system to be configured for common, zonal or two stage alarm. A two wire system can offer a higher level of system flexibility for the installation and operation of the system. Up to 25 per cent saving on time and costs It is estimated that savings on a total installation cost for an eight zone, two wire system could be up to 25 per cent when two core zone cables are wired in, enabling a single circuit per zone to be used both for detection and to power the sounding devices; bringing significant reductions in the overall amount of wire or conductors needed to facilitate the installation. What’s more, a two wire system can offer a higher level of system flexibility for the installation and operation of the system, with increased functionality, such as fault conditions, isolation and zone recognition. A two wire fire loop is also far simpler to wire to circuit schematics that permit less demanding circuit supervision and maintenance routines over the period of the installation. Minimising false alarms There can be no doubt that the two wire approach for smaller installations is far less costly than for an addressable system. As previously highlighted, this is because two wire systems use less expensive cabling and the detectors, manual call points, sounders and beacons all share the same cable. Control panels for two wire systems are typically available with two, four or eight zones, which means that these two wire configurations, in terms of economies of scale, are particularly suited to HMOs, such as student accommodation, hostels or shared flats and houses with bedsits. So how does a non-addressable system mitigate unwanted alarms when compared with an analogue-addressable system of loop devices (detectors, call points and other interface units) that have ID addresses assigned them, with the intelligence to identify, via the control panel’s searching interrogation, the precise location, zone and status of the responding device? One answer can be found in sounder associated verification features like those included in Kentec’s range of Sigma CP-A AlarmSense compatible two, four and eight zone fire alarm control and indicating panels, which, through their use of the latest two wire system technology, have the facility to respond selectively to alarm signals, with local and general alarm switching options available for configuration. With this system, selection of the Alarmsense local alarm feature at the sounder bases, or sounder beacon bases, triggers the alarm verification feature against a configured number of confirmation checks. By making each individual dwelling a zone, only one zone is likely to indicate an initial fire alert, thereby identifying the general area of the fire. When sounder or sounder beacon bases are selected for local alarm mode, any alarm sounders are restricted such that only the sounder connected to the activated detector will operate initially. The panel will attempt to reset the activated detector after a time delay and if successful no further alarms are sounded. AlarmSense’s Prority and Non-Priority signalling feature gives a tenant two minutes to clear the source of the unwanted alarm before a full scale evacuation is initiated. If, however, the detector remains in alarm, all occupants are alerted and the building can be evacuated. The risk of false alarms is a hazard all fire detection systems are susceptible to, but the situation of HMOs and their potentially vulnerable tenants make the potential consequences even greater. 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