Emergency power keeps life safety systems running when the normal supply fails, so people can see, be warned and get out, and so firefighters have what they need. Standby power keeps other things running, such as heating, elevators for convenience, computers or production, because the owner wants it. The two often share a generator, but codes treat them very differently, and the emergency side has to be designed, separated and tested to a higher standard.
Emergency power
Emergency power is required by the building code for certain buildings and systems. Which buildings need it, and for what, depends on the occupancy, the height and size of the building and the systems installed. The National Building Code of Canada and the provincial building codes based on it set out these requirements, and CSA C282 covers the design, installation, maintenance and testing of emergency electrical power supply systems for buildings. Provinces adopt editions at different times, so the engineer of record confirms what applies.
Loads commonly served by emergency power include:
- Emergency lighting and exit signs on egress routes
- Fire alarm systems
- Fire pumps, where installed
- Firefighters' elevators in high buildings
- Smoke control fans and related dampers, where the design relies on them
- Other systems the code or the fire safety design requires to keep working
Some of these loads can instead be served by batteries. Emergency lighting is often provided by unit equipment with built-in batteries, and fire alarm panels have their own standby batteries. Whether a generator is needed depends on the building and the code requirements.
Standby power
Standby power, sometimes called optional standby, is anything the owner chooses to back up beyond what the code requires. Typical examples:
- Heating and freeze protection, which can be essential in a Canadian winter even if not code-required
- Passenger elevators beyond those required for firefighters
- Sump pumps and sewage pumps
- IT rooms, phone systems and security systems
- Refrigeration, process equipment and production lines
- Tenant loads that need power during outages
The owner decides what goes on standby based on the cost of an outage. Some loads sit in between: a hospital, a data centre or a seniors' residence may have legal or contractual requirements that make some "optional" loads close to essential. Health care facilities have their own standards for essential electrical systems.
Side by side
| Emergency power | Standby power | |
|---|---|---|
| Purpose | Life safety: egress, alarm, firefighting | Comfort, property protection, business continuity |
| Who decides | The building code and fire safety design | The owner, sometimes with insurer or contract input |
| Wiring | Kept separate from other wiring | Ordinary wiring methods |
| Priority on a shared generator | First, and protected from overload | Second, and may be shed |
| Testing | Required, documented, on a set schedule | At the owner's discretion, though good practice is similar |
How the systems are arranged
When one generator serves both, the loads are split across separate transfer switches, and emergency wiring is kept separate from the rest of the building's wiring. This is the arrangement the diagram shows.
Key design points:
- Priority. The emergency loads must get power first and must not be put at risk by standby loads. Larger systems use load shedding so that if the generator is overloaded, standby loads drop before emergency loads are affected.
- Separation. Emergency feeders and branch circuits are kept separate from normal wiring, in their own raceways and enclosures, so a fire or fault in the normal system does not take them out. The Canadian Electrical Code sets rules for this.
- Fire protection of wiring. Some emergency circuits must keep working for a period during a fire, which affects cable type and routing.
- Coordination. Protective devices on emergency systems are designed so that a fault on one circuit does not take out others. See selective coordination.
- Transfer time. Emergency loads must be back on within the time the applicable standard allows. Loads that cannot tolerate any interruption need a UPS or batteries as well. See UPS systems for buildings.
- Fuel. The fuel supply must be enough for the run time the code requires for emergency loads, in addition to whatever the owner wants for standby.
Testing and maintenance
Emergency power systems need regular, documented testing, including running the generator under load and transferring through the ATS by simulating a utility failure. CSA C282 sets out testing and maintenance requirements for emergency generators. Standby-only systems are not bound by the same requirements, but the same practices are what make them reliable. See standby generator maintenance.
- A written log of every test, with run time, load, transfer and retransfer times and any alarms
- Tests that simulate a real utility failure, not only a manual generator start
- Confirmation that every transfer switch returns to automatic after a test
- Periodic checks that the load on the generator still matches the design, as loads are added over time
- Emergency lighting tests on battery units, done separately
A typical case
An older mid-rise apartment building has a generator that was installed for emergency lighting and the fire alarm. Over the years, sump pumps, a boiler and a passenger elevator were connected to the same emergency panel because it was convenient. When the building loses power on a cold night, the generator starts but trips on overload when the elevator and boiler start together, and the building is left with only battery emergency lights. A review separates the loads: life safety loads go back on the emergency transfer switch, the boiler and sump pumps go on a new standby transfer switch with load shedding, and the elevator is placed on standby with a controlled start. The generator size is checked against the new arrangement. See how generators are sized.
Do not add loads to emergency panels. Connecting non-emergency loads to an emergency panel is a common and dangerous shortcut. It can overload the generator and compromise the separation the code requires. Any new load on emergency or standby power should be reviewed by an engineer first.
How ehZee can help
Our emergency and standby power design work starts by sorting out which loads are code-required and which the owner wants backed up, then designs the generator, transfer switches, distribution and load shedding to suit. Drawings for permit are sealed by a licensed professional engineer where required, and installation is done by licensed electrical contractors under permit.
Common questions
Can one generator serve both emergency and standby loads?
Often yes, provided the emergency loads have their own transfer switch and wiring and are given priority, usually through load shedding. The design must meet the applicable code and standard.
Do we need a generator for emergency lighting?
Not necessarily. Many buildings use battery unit equipment for emergency lighting. Whether a generator is required depends on the building code requirements for your building and what other systems need emergency power.
Who tests the emergency generator?
The owner is responsible for making sure it is tested and maintained as required. The work is usually done by building staff for routine checks and a qualified service contractor for load tests and maintenance.