Support

Emergency Power Supplies

Central Battery Source

Advantages:

• Maintenance and routine testing is easier with only one location to consider
• Superior battery life, between 5 and 25 years dependant upon type
• Environmentally stable in a protected environment, luminaires able to operate at relatively high or low ambient temperatures
• Large batteries are cheaper per unit of power and luminaires are usually less expensive

Disadvantages:

• High capital equipment costs
• High installation and wiring costs with essential MICC or Pirelli FP200 type cable to each slave luminaire
• Poor system integrity - failure of battery or wiring circuit can disable a large part of the system
• Requirement for 'battery room' to house cells and charger circuits etc, may also require ventilation of acid gases
• Localised mains failure may not trigger operation of emergency lighting in that area Voltage drop on luminaires wired furthest from the central battery could become a problem

Self Contained - Single Point

Advantages:

• Speedy and low cost installation
• Standard wiring material may be used (failure of mains supply due to cable burning through will automatically satisfy the requirement for a luminaire to be lit)
• Low maintenance costs - periodic test and general cleaning only required
• Low hardware equipment costs - no requirement for extended wiring,special ventilation etc.
• Greater system integrity with each luminaire independent of the other
• System can easily be extended with additional luminaire's
• No special sub-circuit monitoring requirements

Disadvantages:

• Limited environmental operating range (batteries may be adversely affected by a relatively high ambient temperature)
• Battery life is limited to between 2 and 4 years dependant upon application
• Testing requires isolation and observation of luminaire's on an individual basis.

In general then, the decision to use either a central battery or a self-contained system is likely to be cost dominated. If an installation has longevity and low maintenance as priorities, then the higher cost of central battery may be acceptable on a very large project. Usually, luminaire and installation costs will be a major consideration, particularly on smaller jobs, and it is this criterion which makes the self-contained luminaire the most popular choice.