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 .

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 . In an HMO , falsely raising a general alarm creates anxiety and is hugely disruptive . The verification feature of AlarmSense enables the investigation of an alarm in a single dwelling . If the detector reactivates after being reset , a general alarm will sound throughout the premises . Activation of a second detector or a call point will sound the general alarm immediately . This discrimination between false and real alarm actuation has huge benefits , obviously , as a

fire signal from a single apartment may well indicate nothing more than someone has burned the toast or lit a cigarette .

Versatility

A two wire system can offer a higher level of system flexibility for the installation and operation of the system .

Two wire systems can not only indicate the apartment in which the actuation has taken place but , in the best systems , will also show whether the actuation originates from an automatic detector or a manual call point .

A valuable feature of advanced two wire alarm systems is the continuity of circuitry should a detector head be removed . The fire detection system continues to operate as intended , supported by the constant monitoring of detector heads for unauthorised removal or disablement .

It ’ s this kind of versatility that makes the two wire system the ideal choice for HMOs , especially when it is the case that the budget for an HMO ’ s fire alarm installation is invariably constrained . Indeed , many contractors claim that the chance of an HMO budget running to a sophisticated addressable fire alarm system is , for all practical purposes , remote .

These reasons are why contractors favour not only a versatile system but one that allows the whole circuitry to be installed economically using only one pair of wires .

Jonathan Gilbert is general manager global sales at Kentec Electronics . Jonathan ’ s expertise ranges from commercial , industrial and oil & gas to marine & offshore applications , not only with fire systems but also security and BMS .

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