Central Battery Systems

Centrally switched systems handle the changeover from mains supply to central battery supply during mains failure at a central changeover relay, usually at the distribution board or at the central battery itself. These are sometimes call “hold off” systems as the central battery system holds the supply off until a power failure occurs. These systems are lower cost than locally switched systems as each emergency luminaire does not contain a changeover relay, however they also have a single point of failure should the single changeover relay fail so locally switched systems are more popular from a reliability perspective.

Centrally switched emergency luminaires only require a single live feed, this carries the mains supply in normal operation, during a power failure the central relay switches the supply to the battery and supplies the luminaire through the same feed as the mains, hence the wiring requirements for centrally switched systems are generally more simplistic and lower cost.

• Centrally switched systems typically operate at 230v. As there is no changeover relay in the luminaire or emergency control gear the central battery runs the mains driver in the luminaire during power failure.
• As the luminaire operates from the mains driver during power failure it provides 100% of its output in emergency operation, 230v centrally switched central battery systems are therefore often used where high lux levels are required during mains power failure for high risk areas or where staff must remain to continue working on critical activities.
• Centrally switched luminaires only require live, earth and neutral connections and the single live connection carries either the mains supply in normal operation or the central battery supply during power failure. A ceramic terminal block is also required in most instances depending on how the installation has been wired.

Central battery systems have specific requirements for their cabling to ensure they provide a safe and robust system. The cabling carrying the central battery supply must be fire rated to ensure that during a fire the cabling cannot burn through and disconnect power from other parts of the building where people may still be trying to evacuate. All parts of the cabling system must meet this fire rated standard including joints, for this reason the terminal block in the luminaire must be ceramic where it is used for loop in / loop out wiring methods. If luminaires are wired from spurs from the fire rated cabling system the cable in the spur itself and the terminal within the luminaire do not need to be fire rated, however such spurs must not exceed one metre in length. All fire rated cabling must be contained in metal conduit secured with metal clips to prevent it falling from the ceiling during a fire and causing an electrical shock hazard to emergency workers.

The above is not an exhaustive list of all central battery systems and installation requirements but is intended to act as a guide to provide a basic understanding of these systems and some of the critical information to consider when specifying luminaires for a central battery system. There are a variety of other central battery systems on the market, for example older central battery systems may operate a dedicated emergency lamp in the luminaire entirely separately from the mains source. Such systems were commonly used in older high intensity discharge luminaires where the strike time of the lamp was too slow to work as an effective emergency light source hence a separate halogen lamp would be used to provide a light source capable of instantly striking. Specifying the incorrect luminaire for a central battery system can be extremely costly so it is important to ensure that the system is fully understood prior to placing your order and we would always recommend seeking the advice of a specialist to ensure that the cabling system is compliant with the latest regulations.