Standby power / secondary supply

Standby power is the secondary supply that keeps a fire alarm system running when normal power fails, and in Canada its duration is set by the building code, not by a CAN/ULC standard. In Ontario the requirement is 24 hours of supervisory operation followed immediately by emergency power under full load, and that second period is 2 hours, 1 hour, 30 minutes or 5 minutes depending on the building. The familiar shorthand of 24 hours plus 30 minutes is only the default case, and 24 hours plus 5 minutes is an unsafe blanket answer. The supply may be batteries, a generator, or a combination, and transfer must be immediate and automatic with no loss of information.

Last updated: September 2026

The one thing worth knowing

The duration comes from the building code, which is free to read. The calculation method comes from CAN/ULC-S524, which is paywalled. Those are two separate questions and they have two different answers, and most of the confusion in this subject is people answering one while thinking about the other.

This entry covers the duration. The method is in battery calculation.

What Ontario requires

The Ontario Building Code article is titled Emergency Power for Fire Alarm Systems and requires a supply capable of supervisory operation for not less than 24 hours, followed immediately by emergency power under full load for a period that depends on the building:

Building	Emergency power under full load
Within Subsection 3.2.6	2 hours
Group B major occupancy outside Subsection 3.2.6	1 hour
Containing a Group C retirement home	1 hour
Within the two articles the code names for certain occupancies	1 hour
Not requiring an annunciator	5 minutes
All other buildings	30 minutes

The supply may be a generator, batteries, or a combination of the two. Transfer must be immediate and automatic on failure of the normal source, with no loss of information.

Provenance, stated plainly. We read this article as 3.2.7.8 in two unofficial online reproductions of the Ontario Building Code, one of which states it is reproducing the 2024 Building Code, O. Reg. 163/24, and carries cross reference numbers consistent with that edition. Ontario's own 2024 examination syllabi confirm that Subsection 3.2.7, Lighting and Emergency Power Systems, exists in the current code, but do not go to article level for it. So: treat the durations as reliable and confirm the article number against the free 2024 Building Code Compendium before you put it in a compliance document. Article numbers move between editions, which is the same trap the CAN/ULC edition tracker covers for standards.

Read the categories, not the slogan

Three of those six rows catch people out.

"Not requiring an annunciator" is why 5 minutes exists. It is the small building case, and it is tied directly to the annunciator question. Get the annunciator determination wrong and the battery size changes underneath you.

A retirement home pulls a building to 1 hour whether or not anything else about it would.

Subsection 3.2.6 pulls a building to 2 hours, and that is the same subsection that requires a CACF. If the building has a CACF, the answer is 2 hours.

The CFAA's own journal states the general Canadian position the same way: 24 hours in standby followed by an alarm duration specified by the National Building Code, typically ranging from 5 minutes to 2 hours. Anyone quoting a single figure for every building is quoting a habit.

How it behaves in the field

Supervisory load is not the same as alarm load. Twenty four hours is served at the system's quiescent draw. The second period is served at full load, with every notification appliance operating. Those two numbers differ by an order of magnitude on most systems.

Every power supply needs its own answer. A transponder or a remote booster with its own batteries needs its own duration met, not just the main panel.

Generators do not remove the batteries. Where a generator provides the emergency power, the transfer still has to be immediate with no loss of information, which in practice means batteries carry the system through the transfer.

What goes wrong

Batteries age. The Ontario Fire Code side of this is inspection and testing to CAN/ULC-S536, which added a defined silent accelerated battery test method in its 2019 edition. A battery that met the calculation on day one and has not been load tested since is a deficiency waiting to be written up.

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