Emergency Power

Emergency power keeps essential loads running when the normal supply fails: standby generators with their fuel systems, automatic transfer switches and exhaust; uninterruptible power supplies (UPS) with their batteries; and the distribution that carries emergency power to the loads. Some loads are life safety (fire pumps, smoke control fans, fire-fighting lifts, emergency lighting central systems); others are business continuity (data rooms, refrigeration, critical tenants). Healthcare buildings combine both, with the strictest requirements.

The question that matters is not whether a generator exists but which loads it actually supports, whether it can carry them, and whether it has been proven to start and run under load recently. Load growth, tenant additions and changes to fire systems often put loads on the emergency supply that the generator was never sized for.

What shortens life:

• Running unloaded during weekly tests, which causes wet stacking in diesels.
• Hot battery rooms: every 10 °C above about 20 to 25 °C roughly halves lead-acid battery life.
• Water in fuel from condensation and tank breathing.
• Lack of exercise: generators that never run under load fail when needed.
• Deferred battery replacement.

Failure to start

The commonest reason a generator fails in an emergency is that it does not start: flat or failed starting batteries, failed charger, failed coolant heater in cold climates, air in the fuel system, or a fault in the controller. Each is cheap to prevent and invisible without testing.

Wet stacking

Diesels run at light load do not reach operating temperature; unburnt fuel and carbon build up in the exhaust and cylinders. The engine then smokes, loses power and may fail when asked to take full load. Weekly no-load runs cause it; regular load bank testing prevents it.

Fuel degradation

Diesel stored for long periods takes up water, grows microbes at the fuel-water interface (diesel bug), oxidises and forms sludge. Filters block in the first hours of running, exactly when the generator is needed. Biodiesel blends degrade faster.

Transfer switch faults

Transfer switches that are rarely operated can stick, and settings changed during maintenance can stop them transferring or prevent return to mains. A transfer switch failure looks like a generator failure to the building.

UPS failures

UPS batteries fail first, usually without warning unless monitored; a UPS with failed batteries drops its load the instant the mains fails. Capacitors and cooling fans age and need replacement at mid-life. Lithium battery systems introduce fire risks that need separation and detection.

Capacity and load mismatch

Loads added to emergency boards over the years can exceed the generator's capacity; large motor loads such as fire pumps and smoke fans starting together can stall it. Life-safety loads must be given priority and the generator must carry them.

Exhaust, ventilation and noise

Generator rooms need combustion and cooling air; blocked louvres and recirculated exhaust cause overheating. Exhaust discharge near air intakes and windows brings fumes into the building. Noise and air emission limits constrain where and how long generators can run.

In the generator and UPS rooms

• Nameplates: rating, year, run hours.
• Battery dates and condition; charger status.
• Coolant heater working (engine block warm).
• Fuel tank level, gauges, water in sight glasses; bund condition and contents.
• Exhaust soot and oil leaks.
• Louvres clear; room temperature.
• UPS alarms; battery room temperature.

In the records

• Test logs: weekly or monthly runs, with load and duration.
• Load bank test reports.
• Fuel test results.
• Battery test and replacement records.
• Transfer switch tests.
• List of loads on emergency supply and the load study.
• Records of real outages and how the system performed.

Findings are graded by what they demand: safety (can hurt someone now), failure (failed and damaging the building), condition (distress present and progressing), lifecycle (renewal due on age and exposure), deadline (a regulator or ordinance sets the date), check (investigate before sizing works) and nil (cosmetic or stable).

An electrical engineer leads, with the generator and UPS maintenance contractors.

• Records review: test logs, load bank reports, fuel analysis, battery records, maintenance, outage history.
• Inspection of generator, fuel system, transfer switches, UPS and batteries, rooms and exhaust.
• Load bank test at or near rated load for a sustained period.
• Black-start test: simulated mains failure with transfer of real loads.
• Fuel sampling for water, microbes and contamination.
• Battery testing by impedance or discharge.
• Load study: what is on emergency supply, life-safety priority, starting sequence, capacity.

The report should state whether the system is proven to carry its loads, the life-safety position, condition and remaining life, and works needed.

• Transfer switch test: transfer, retransfer and timing, with settings recorded.

Tests are planned with the building so critical tenants and life-safety systems are covered throughout.

• Testing regime: exercise generators monthly under meaningful load, run periodic load bank tests at or near rated load, and run full black-start tests transferring real loads; record every test.
• Starting system: replace starting batteries on a fixed cycle, check chargers and coolant heaters, and fit monitoring that alarms on battery or charger faults.
• Fuel management: test fuel periodically; polish and treat it; remove water; turn fuel over; maintain tanks, bunds, vents and leak detection.
• Generator overhaul at run-hour or age intervals, or replacement where parts and controls are no longer supported.
• UPS maintenance: replace batteries on a cycle with monitoring; replace capacitors and fans at mid-life; replace the UPS at end of life.
• Load management: remove non-essential loads from emergency boards, sequence the starting of large motors such as fire pumps and smoke fans, and increase capacity where the life-safety load needs it.
• Load bank connection point so testing can be done without disconnecting the building.
• Room and exhaust works: clear louvres, extend exhaust away from intakes, add acoustic treatment.
• Battery safety: separation, ventilation and detection for lithium and large lead-acid installations.

Testing, fuel management and maintenance are recurring contracts; load bank tests and fuel polishing are recurring lump sums. Starting and UPS batteries are replaced on a cycle and are best carried as recurring allowances. Generator replacement is a lump-sum project including the generator set, crane lift, fuel system, exhaust and acoustic works, switchboard and transfer switch changes, and commissioning, with temporary generation where life-safety loads must remain covered. UPS replacement is similar.

Life-safety testing and rectification are code compliance; batteries and fuel management are repairs and maintenance on a cycle; replacement is lifecycle; capacity increases sit with the project that adds load.

• Australia. AS/NZS 3010 covers generating sets, AS/NZS 3009 emergency power in hospitals, and AS 1940 fuel storage; generators supporting fire systems are maintained as essential safety measures.
• United Kingdom. BS 7698 and BS ISO 8528 cover generating sets; BS 9999 and BS 5839 set life-safety supply requirements; healthcare follows HTM 06-01.
• United States. NFPA 110 sets testing for emergency and standby power systems, including monthly exercise under load for at least 30 minutes and a four-hour test every three years for Level 1 systems; NFPA 111 covers stored energy systems; NFPA 70 Articles 700, 701 and 702 cover emergency, legally required and optional standby systems.

Environmental permits also apply in all three jurisdictions to larger diesel generators, limiting running hours and emissions, which affects testing regimes.

• Generator and UPS test logs with load and duration.
• Load bank test reports.
• Fuel analysis results and fuel management records.
• Starting and UPS battery test and replacement records.
• Load study and the list of loads on each emergency board.
• Outage history and how the system performed.
• Maintenance contracts and service reports.
• Generator run hours, installation date and overhaul history.
• Environmental permits for the generator where required.