Essential Services and Life Safety Power

What You Need to Know

Some building systems must keep running when the mains power goes out. Fire pumps, emergency lighting, exit signs, smoke control fans, and fire alarms all need power during a blackout. The NCC calls these “essential services.” If they lose power, people cannot get out safely. AS/NZS 3000 Clause 7.2 sets the wiring rules. AS/NZS 3010 covers the generator installation. Get the generator too small or the transfer switch wrong, and the building will not pass final inspection.

• Essential services wiring must be on separate circuits from general power. These circuits must not share switchboard sections with non-essential loads. (AS/NZS 3000, Clause 7.2)
• Fire-rated cables are required for essential services. The wiring system must survive fire and mechanical damage for the duration needed. Ratings follow AS/NZS 3013 wiring system classifications. (AS/NZS 3000, Clause 7.2; AS/NZS 3013)
• Emergency lighting must reach 10% illuminance within 1 second, 80% within 15 seconds, and full illuminance within 60 seconds of a mains failure. Battery systems must last at least 90 minutes. (NCC Part E4, EV4.1; AS 2293.1)
• The generator and normal supply must never connect to the installation at the same time. The changeover device must provide full electrical isolation. (AS/NZS 3010, Clause 3.3)
• A four-pole automatic transfer switch is recommended. It switches the neutral along with the three phases, preventing parallel neutral paths and circulating currents. (AS/NZS 3010)
• The NCC requires emergency equipment to keep working for as long as it is needed. Protection levels depend on the equipment and the building situation. (NCC Part E, Performance Requirement CP7)
• Fire pumps need backup power. The generator must handle the locked rotor amps of one pump starting while another pump runs at full load. (AS 2941; AS/NZS 3000 Clause 7.2)
• Fuel storage must cover at least 4 hours of operation if the generator only starts during fire events, or 8 hours if it starts on any mains failure. (Industry practice aligned with AS/NZS 3010)

Take a 10-storey commercial office building. The essential services load list looks something like this: fire pump at 55 kW, stairwell pressurisation fans for two stairs at 30 kW total, emergency and exit lighting at 15 kW, fire alarm and EWIS panel at 5 kW, smoke exhaust fans at 40 kW, one fire-rated lift at 30 kW, and BMS fire mode controls at 5 kW. That adds up to about 180 kW of running load.

But the fire pump pulls around 350% of its rated current on startup - roughly 190 kW for the first few seconds. If the stairwell pressurisation fans start at the same time, you get another spike. A 180 kW generator will stall.

You need to size for the worst-case starting sequence. In this example, a 350 kVA (280 kW) diesel generator handles the starting loads with margin. The generator runs at about 65% load during normal emergency operation, which sits in the ideal 60–80% range for diesel efficiency and reliability.

The automatic transfer switch sits between the mains supply and the essential services distribution board. When mains power drops out, the ATS signals the generator to start. The generator reaches stable voltage and frequency in about 10–15 seconds. The ATS then switches the essential loads to the generator. When mains power returns, the ATS waits for a stable period (typically 5–10 minutes), then switches back and shuts down the generator after a cool-down run.

The generator needs its own room with fire-rated walls (minimum 120 minutes FRL), ventilation for combustion air and heat rejection, fuel storage with bunding, and exhaust flue routing to atmosphere. On rooftop installations, the roof slab must provide adequate fire separation from the floors below.