CAN/ULC‑S573: The Technical Standard Behind Ancillary Devices Connected to Fire Alarm Systems
Every modern building does more than sound an alarm when a fire occurs. Corridor doors release, elevators recall, HVAC equipment shuts down or changes mode, dampers respond, and other building systems move into a life safety sequence. Those actions depend on ancillary devices that interact with the fire alarm system, and CAN/ULC‑S573 is the technical standard that defines how those devices are to be applied and installed.
CAN/ULC‑S573 is formally titled Standard for Installation of Ancillary Devices Connected to Fire Alarm Systems. The first edition was published in 2018. The standard describes requirements for the application and installation of ancillary devices that interact with a fire alarm system. It is not a replacement for CAN/ULC‑S524; it is applied in conjunction with CAN/ULC‑S524, which remains the core installation standard for the fire alarm system itself.
What the standard covers
The scope of CAN/ULC‑S573 is specific: it addresses ancillary devices that interact with a fire alarm system. In technical terms, these are devices or subsystems that are not themselves the core fire alarm system, but are controlled by it, monitored through it, or otherwise interfaced to it so that a fire alarm condition produces a required building response.
Typical examples in the field include magnetic door holders, elevator recall interfaces, HVAC shutdown controls, smoke control interfaces, dampers, shutters, electrically locked door release arrangements, and similar control or monitoring points tied to fire alarm operation. The common factor is that the fire alarm system initiates, supervises, or receives status from these external functions, so the interface cannot be treated as informal field wiring.
The standard is intended to apply to ancillary device installations for both required and voluntary fire alarm system installations. That makes it relevant not only in fully mandated fire alarm installations, but also wherever a voluntary system includes ancillary interfaces that must operate reliably and in a documented manner.
Why S573 matters technically
Before S573, ancillary connections were often handled through a mixture of manufacturer instructions, project specifications, and trade practice. That approach created inconsistency in how interfaces were selected, wired, supervised, documented, and verified, especially when multiple trades were involved in the same life safety sequence.
S573 helps standardize that work by giving the industry a dedicated installation framework for ancillary devices connected to fire alarm systems. This matters because ancillary connections directly affect system performance during alarm, supervisory, and trouble conditions, and failures at these interface points can prevent the building from responding as intended during an emergency.
From a practical standpoint, the standard supports more consistent expectations in areas such as:
Application of ancillary devices and their interface methods
Installation quality and consistency across fire alarm, electrical, mechanical, and elevator scopes
Documentation of ancillary functions on drawings, sequences, and supporting manuals
Verification and testing of the required building response once the system is commissioned
Relationship to CAN/ULC‑S524 and other standards
A key technical point is that CAN/ULC‑S573 must be read alongside CAN/ULC‑S524, not in isolation. S524 addresses the installation of the fire alarm system itself, while S573 addresses the ancillary devices that connect to and interact with that system. When a project includes control relays, input or output modules, or monitored interfaces to external building systems, the design and installation team needs to determine where S524 governs the fire alarm side and where S573 governs the ancillary interface side.
In practice, S573 also affects work that later appears in verification, inspection, and integrated testing activities. Ancillary circuits such as elevator recall, HVAC shutdown, and door release must be documented and tested as part of acceptance and ongoing system review, which is why undocumented or poorly coordinated ancillary connections routinely create problems late in a project.
This is also where coordination with CAN/ULC‑S537 (verification), CAN/ULC‑S536 (inspection and testing), and CAN/ULC‑S1001 (integrated systems testing) becomes important at the project level. Even when those standards govern later phases of verification, inspection, or integrated systems testing, the quality of that work depends on the ancillary installation having been properly designed, installed, and documented from the outset.
What counts as an ancillary device in practice
For technicians and designers, the easiest way to understand S573 is to look at function rather than product category. If the fire alarm system sends a signal that causes another building system to perform a life safety action, or if the status of that external function is monitored through the fire alarm system, the interface is within the type of installation S573 was created to address.
Examples commonly encountered on projects include:
Electromagnetic door holders and door release circuits
Elevator recall and associated monitored interface points
Fan shutdown, air handling unit shutdown, smoke control, and damper interface circuits
Stairwell pressurization interfaces and related control logic
Electrically locked door release or controlled egress arrangements where the fire alarm system forms part of the release strategy
These systems may involve low‑voltage interfaces, monitored relay logic, addressable modules, or connections that cross into other electrical equipment scopes. That is exactly why a dedicated installation standard is necessary: the fire alarm panel may only provide the initiating or supervisory logic, but the life safety outcome depends on the entire ancillary pathway working as designed.
Common compliance issues in the field
Experience in the field shows several recurring problem areas that S573 is intended to address.
Undocumented ancillary connections
Devices are often added or revised during construction, but the fire alarm drawings, sequence of operation, or verification package are never updated. When that happens, the installed system no longer matches the documented design, and verification becomes difficult or impossible to complete cleanly.
Inadequate supervision or poor interface selection
If the ancillary circuit is not arranged in a way that supports the required fault monitoring or reliable transfer of the fire alarm control signal, the system can appear normal until an emergency or test exposes the problem. The purpose of S573 is not simply to indicate where to land conductors; it is to ensure the ancillary connection performs predictably as part of a life safety system.
Trade coordination gaps
HVAC shutdown, smoke control, elevators, access control, and door hardware often sit in different contractual scopes, but the fire alarm system is expected to initiate or monitor the final function. Without clear delineation of interface points, compatible hardware, and sequence logic, projects end up with gaps between what was specified, what was installed, and what can actually be verified.
Why this standard belongs in technical training
CAN/ULC‑S573 is a technical standard with direct field consequences. It affects how designers write sequences, how technicians install modules and relays, how electricians coordinate with mechanical and elevator trades, and how verifiers confirm that a building’s intended life safety response actually occurs.
For training and certification programs, S573 is valuable because it formalizes a discipline that is often learned informally on site: how to treat ancillary devices as part of a coordinated life safety strategy rather than as miscellaneous extras. That is especially important as projects become more integrated and more dependent on documented interfaces between fire alarm, access control, mechanical systems, elevators, and smoke management equipment.
Final perspective
A fire alarm system is not judged only by whether it can indicate alarm; it is judged by whether the connected building functions respond correctly when the signal occurs. CAN/ULC‑S573 exists to support that outcome by establishing requirements for the application and installation of ancillary devices connected to fire alarm systems and is intended to be applied in conjunction with CAN/ULC‑S524.
For contractors, designers, verifiers, and owners, the message is straightforward: ancillary interfaces need the same level of technical discipline as the rest of the fire alarm system. When those interfaces are properly designed, installed, and documented, the project is easier to verify, easier to maintain, and more likely to perform as intended when the building depends on it.