Self-contained vs central battery emergency lighting

What supply systems are there?

Every emergency lighting installation needs a power source that works independently of the normal supply. There are three basic principles:

• Self-contained system: a self-contained luminaire is an emergency luminaire with its own built-in battery, charger and changeover device. The requirements for such luminaires are set out in EN 60598-2-22.
• Group battery system: a group battery system is a central power supply with limited output that supplies a manageable number of luminaires. EN 50171 refers to it as an LPS (low power supply system).
• Central battery system: a central battery system is a central power supply without that output limit, supplying all the emergency luminaires in a building or in large parts of it. EN 50171 refers to it as a CPS (central power supply system).

Whatever the system, the same photometric requirements of EN 1838 and the same testing duties under EN 50172 apply. The system does not decide whether the requirements are met, but how. For an overview of the standards, see emergency lighting standards.

How do the systems compare in detail?

The table describes typical characteristics. Which design is permitted in a specific case depends on the building permit, the fire safety strategy and national rules.

What requirements apply to cabling and rooms?

This is the biggest practical difference. In a self-contained system the energy source sits in the luminaire itself. The supply cable does not have to deliver power in an emergency; if it is destroyed by fire, the luminaire switches to its battery.

With group and central batteries it is the other way round: the cables from the unit to the luminaires must keep working for a certain time in a fire. How long, and with which cable systems, is set nationally. In Germany, for example, the Model Wiring Installations Directive (MLAR), as adopted by the federal states, generally requires 30 minutes of circuit integrity for emergency lighting, typically achieved with cable systems rated E30. Depending on cable routing, fire compartments and local law there are relaxations and deviations; other countries have their own rules. The fire safety strategy is what counts.

Then there is the location of the battery unit. Central batteries are usually housed in a dedicated electrical operating room that must be structurally separated and adequately ventilated – in Germany according to the federal states' regulations on electrical operating rooms (EltBauVO). Group batteries are also subject to location requirements. These building-related costs are often overlooked when only equipment prices are compared.

What about maintenance and monitoring?

With a central battery, maintenance is concentrated in one place: battery, charger and monitoring equipment sit together. Modern units monitor every connected luminaire and report faults centrally. In return, EN 50172 and national rules such as DIN VDE V 0108-100-1 additionally call for daily visual checks of the indicators on central systems.

With self-contained luminaires, the effort is spread across many devices. In the past that meant testing every luminaire by hand and replacing every battery individually. Automatic test systems to EN 62034 have changed this considerably. Self-testing luminaires carry out function and duration tests themselves and report the result via status LED, bus or app – see self-testing emergency lights. Long-life batteries such as LiFePO4 also extend replacement intervals; see emergency light batteries.

Which system suits which building?

There is no one-size-fits-all answer. These questions help as a guide:

• How many luminaires are needed? With a few to several dozen luminaires, self-contained systems usually have the edge. With very many luminaires, the central effort is more likely to pay off.
• New build or existing building? In existing buildings, retrofitting fire-resistant cabling is often complex and costly. Self-contained luminaires use the existing supply.
• Is there space for a battery room? If not, a central battery is practically ruled out or requires alterations.
• How will the use change? With frequent refurbishments, tenant changes or extensions, self-contained luminaires can be added more flexibly.
• What do the building permit and fire safety strategy require? In some high-risk or high-occupancy buildings the fire strategy sets specific requirements that limit the choice.
• What are the ambient conditions? Very high or very low temperatures put more strain on batteries inside luminaires than on a battery in a temperature-controlled room.

For many commercial buildings – offices, practices, shops, restaurants, warehouses and workshops – modern self-contained luminaires with self-test are now an economical solution. They are particularly suitable for upgrades; see upgrading emergency lighting.

How does NOTLUX approach this?

NOTLUX Series 19 luminaires are self-contained luminaires with an integrated LiFePO4 battery, automatic self-tests to EN 50172 and EN 62034, and Bluetooth connectivity for the digital logbook. For existing LED fittings there are also emergency drivers that turn an existing luminaire into an emergency luminaire. Which system suits your building is clarified during an on-site survey.