Emergency Lighting: Self-Contained vs Central Battery Systems

What You Need to Know

Every commercial building needs emergency lighting. When the power fails, these lights guide people to the exits. AS/NZS 2293.1 gives you two main options: self-contained batteries inside each fitting, or one central battery feeding all fittings through fire-rated cables. Your choice comes down to building size, upfront budget, and what you want to spend on maintenance over the next 10 years.

• Emergency lighting must reach 10% output within 1 second, 80% within 15 seconds, and full output within 60 seconds of mains failure (NCC 2025, E4V1)
• Battery duration must be at least 90 minutes from full charge (AS/NZS 2293.1)
• Escape paths need at least 0.2 lux on the centreline at floor level, with an average of 0.5 lux across the path (AS/NZS 2293.1, Cl 3.3)
• Stairways need at least 1 lux on each step (AS/NZS 2293.1, Cl 3.3)
• AS/NZS 2293.1 allows three system types: self-contained, single-point, and central battery (AS/NZS 2293.1, Cl 1.1)
• Central battery submains and final subcircuits must use WS4X fire-rated wiring per AS/NZS 3013, providing 90 minutes of circuit integrity in fire (AS/NZS 2293.1, Section 7)
• Exception: cables under 10 m that stay within one fire compartment do not need fire rating (AS/NZS 2293.1, Section 7)
• All emergency lighting circuits must be unswitched and permanently energised, with 50 mm minimum separation from other wiring (AS/NZS 2293.1, Section 7)

Take a 5-storey Class 5 office building with 500 m² floor plates. You might need 120 emergency fittings across corridors, stairways, and open-plan areas. You have two paths.

Self-contained route: Each of those 120 fittings has its own battery. A licensed electrician wires each one into the normal lighting circuit. No fire-rated cable needed. Installation is fast. But every 4 to 6 years, someone needs to open each fitting, pull the old battery, and install a new one. At roughly $200 per fitting for labour and parts, that is $24,000 per battery replacement cycle. Over 20 years, you could spend $80,000 or more on battery changes alone.

Central battery route: One battery unit sits in a fire-rated room on the ground floor or basement. Fire-rated WS4X cable runs from that room to every fitting on every floor. The cabling alone can double the electrical install cost for the emergency lighting package. Industry estimates put the central unit at $15,000 to $30,000. But when the batteries need replacing in 8 to 10 years, one technician swaps them in one location. Industry estimates suggest $3,000 to $8,000 per replacement cycle instead of $24,000.

Temperature matters. Self-contained batteries sit in ceiling voids where summer temperatures can reach 35 to 45°C. NiCd batteries rated for 10 years at 20°C may only last 3 years at 35°C. LiFePO4 batteries handle heat better and last 6 to 12 years depending on grade. Central battery rooms can be climate-controlled, keeping batteries in their ideal range and extending their life.