This guide explains which loads an emergency generator in a high-rise building usually serves, how the plant is sited and fuelled, and how it is tested. Building and fire codes differ by country and city, so the codes named here are examples; the local authority’s requirements always govern.
Life safety loads come first
The core loads on a high-rise emergency system are those needed to protect life: emergency lighting and exit signs, fire alarm and voice evacuation systems, fire pumps, firefighter lifts, smoke control fans and stair pressurisation fans. Many codes require these to be on a separate emergency system with its own transfer equipment and wiring.
List each life safety load with its rating, starting method and the time within which it must be energised. Some codes require emergency power within a few seconds of a failure.
Fire pumps
Fire pumps boost water pressure to reach upper floors. They are among the largest motors in the building and may start direct on line. If the generator supplies the fire pump, it must be able to start the pump with other emergency loads running, without a voltage dip that drops out contactors or lifts.
In the United States, NFPA 20 sets rules for fire pump power supplies, including how the generator is sized for pump starting. Other countries have equivalent standards. Confirm the pump’s starting method early, because it can set the generator size.
Lifts for firefighters and evacuation
Tall buildings often have firefighter lifts, and some codes now allow or require occupant evacuation lifts. These need emergency power with enough capacity to run the lifts at the required speed. Lift motors with regenerative drives can feed power back during descent, which the generator and its protection must handle, often with other loads present to absorb it.
Coordinate early with the lift supplier on starting current, regeneration and the number of lifts that may run at once.
Smoke control and stair pressurisation
Smoke control fans extract smoke from fire floors, and pressurisation fans keep stairwells free of smoke so people can escape. These fans are critical and often run on variable speed drives. Their combined load can be large and must be available throughout the evacuation.
Check the drives’ behaviour on generator supply, including harmonic distortion and restart after a brief interruption.
Legally required and optional standby loads
Beyond life safety, owners often want the generator to carry other loads: domestic water pumps, some lifts, security, IT rooms, refrigeration or tenant areas. These are usually treated as optional standby and must be on separate transfer switches so that they never delay or overload the life safety supply.
Our generator sizing chart shows how to total the loads and convert between kW, kVA and amps.
Where to put the generator
Roof, podium and basement locations each have trade-offs. A roof position keeps exhaust away from occupants and flood risk but needs a crane for installation, structural support and a long fuel route. A basement is easy to reach for fuel deliveries but is exposed to flooding and needs long air and exhaust paths. A podium level is often a practical compromise.
Wherever it goes, the generator room needs fire separation, ventilation, acoustic treatment and access for maintenance and replacement of major parts.
Fuel storage and delivery
Codes and local fire services limit how much fuel can be stored in a building and where. A common arrangement uses a main tank at or below ground level with pumps lifting fuel to a day tank beside the generator. Fuel lines through the building must be protected and fire rated.
Size storage for the required runtime and plan refuelling during an extended outage. Our article on how long a diesel generator can run continuously covers runtime limits.
Transfer switches and selective coordination
Emergency, legally required and optional loads typically use separate automatic transfer switches, with the emergency switch transferring first. Protective devices must be selectively coordinated so a fault on one branch trips only its own breaker and does not take out the whole emergency supply.
NFPA 70 and NFPA 110 are commonly referenced in the United States for these requirements. Other jurisdictions apply their own electrical and emergency power standards.
Air, exhaust and noise in a dense building
A generator inside a tall building needs a large volume of air for combustion and cooling, and a safe route for hot exhaust. Intake louvres must not draw in exhaust or kitchen fumes, and the exhaust discharge must be placed where it cannot enter windows, fresh-air intakes or neighbouring buildings. Acoustic attenuators on air paths and exhaust silencers keep noise within limits for occupants and neighbours, and the generator room should be designed so that these elements can be inspected and maintained.
Testing and records
Emergency systems in tall buildings are usually tested weekly or monthly and under load periodically, with a full building transfer test at longer intervals. Records of each test are often inspected by the fire authority. Testing should include fire pump and lift operation on generator power, not just a generator run.
Our guide to emergency generator test records explains what to log. Installation points are covered in our page on emergency generator installation.
About the authors
These notes come from our emergency power engineers, who design, install and maintain standby plant for commercial and critical buildings. USP&E is the contractor on that work rather than a broker, with 25,000 MW contracted since 2002, 150+ power projects in 45+ countries and 24+ years in the field. Our O&M support is described on the operations and maintenance page.
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High-rise emergency generator questions
What does an emergency generator power in a high-rise building?
Life safety loads such as emergency lighting, fire alarms, fire pumps, firefighter lifts, smoke control and stair pressurisation, plus any optional loads on separate transfer switches.
Why do fire pumps affect generator size?
Fire pumps are large motors that may start direct on line. The generator must start them with other emergency loads running without an excessive voltage dip.
Is it better to put the generator on the roof or in the basement?
Both work. The roof avoids flooding and keeps exhaust away from people but needs crane access and long fuel lines; the basement eases fuel delivery but faces flood risk.
How often is a high-rise emergency system tested?
Typically weekly or monthly with periodic load tests and longer-interval full transfer tests, following the local code and fire authority.
Plan emergency power for a tower
Send the life safety load schedule and the building’s plant room options, and our engineers will help you size and site the emergency generator.
If a document set is easier than a conversation, send it to info@uspeglobal.com or upload a summary through the emergency power enquiry form; to talk it over, dial +27 10 822 2324. Standby sets in stock are listed in our diesel generator inventory.