How to Read a Fire Alarm Riser Diagram and an Input Output Matrix

Last updated: September 2026

Quick answer

• A riser diagram is a schematic of the system, not a floor plan: the building flattened onto one sheet, showing the control unit, its power supply and every circuit leaving it.
• Read it in the same order every time: control unit, then incoming power and the disconnect, then each circuit traced outward to its last device.
• Class B circuits end at an end of line device. Class A circuits return to the panel instead. The far end of the run tells you the class.
• An input output matrix puts inputs in rows and outputs in columns. A mark in a cell is a required sequence of operation, and a verifier will test every one.
• No Canadian code mandates a fire alarm symbol set. The legend printed on the drawing governs.
• Add up the circuit loading yourself. A notification circuit drawn over its rating becomes your problem at commissioning.
• When documents disagree, the contract decides. Under CCDC 2, General Condition 1.1.5, the specifications rank above the drawings.

What a riser diagram is, and what it is not

Take the building, squash it flat, throw away every wall. What is left is the riser diagram: a schematic showing what connects to what and roughly which floor each thing sits on. Nothing is to scale. A detector drawn halfway up the sheet is on level 3, and that is the only geographic information on offer. The riser answers system questions, the floor plans answer location questions, so if you are working out where a device lands on a wall, you are on the wrong sheet.

CAN/ULC-S524 expects both. In a May 2023 presentation to the Building Officials Association of British Columbia, UL described the S524 documentation requirements as including building plans showing fire alarm zoning, device addresses and the location of each field device, plus "a separate wiring block diagram (i.e., schematic and riser diagram)" showing the interconnections. Two drawings, two jobs. The current edition is CAN/ULC-S524:2019, the eighth edition.

Read it in this order

People who are fast with drawings are not reading faster, they are reading in a consistent order.

1. Find the control unit. The fire alarm control unit is the box everything hangs off. Note the model number beside it, because circuit ratings, loop capacity and battery capacity all come from that manufacturer's data sheet, not from the drawing.

2. Find the incoming power and the disconnect. Look for a note like "120 V from panel LP-1, circuit 3". Section 32 of the Canadian Electrical Code, adopted in Ontario as Section 32 of the Ontario Electrical Safety Code, governs it: Rule 32-108 puts the fire alarm supply on a separate circuit, and the overcurrent device and disconnecting means must be identified as fire alarm, coloured red, and lockable in the on position. That summary comes from Electrical Industry Canada's guide to Section 32, a secondary source, so confirm it against your code book and see Section 32 fire alarm circuits. If the riser does not name the source circuit, ask before rough-in.

3. Trace one circuit at a time, outward. Take the circuit nearest the panel, follow it to its last device, then come back for the next. Read across a busy riser instead and you will miss one.

The three circuit types, and what the lines tell you

An initiating device circuit is a conventional two wire circuit reporting one condition for the whole circuit. Operate any device on it and the panel knows the circuit is in alarm, not which device.

A signalling line circuit is the addressable loop, where every device has an address and reports individually. On Canadian drawings it is often labelled DCL, for data communication link, rather than SLC. Same physical thing, different house style.

A notification appliance circuit feeds the horns, bells and strobes. It carries real current, and it is the circuit most often drawn without anyone checking the arithmetic.

Line types are where consultants diverge. Common conventions are a solid line for conduit, a dashed line for free air cable, short cross ticks for conductor counts, and a doubled or looped line for a Class A run drawn out and back. Common is not universal. Read the legend.

Device counts and spotting an overloaded circuit

Designations look like NAC-1, SLC-1, IDC-2, often with a zone prefix. On the riser the City of Winnipeg posted with a library tender, detection zones run Z-01 and Z-02, the duct detectors get their own ZAHU-01 and ZERV-01, detection circuits are marked Class A and signal circuits Class B. Local naming, but always a designation, a class and a count.

Three numbers decide whether a circuit works, and usually only one is printed on the drawing.

Address count, on a signalling line circuit. The data sheet gives a maximum per loop. Count what is drawn, including the things that take an address without looking like devices: monitor modules, control modules and isolators.

Current draw, on notification circuits. Add the alarm current of every appliance at the settings actually specified, then compare to the circuit rating. Specifications often tighten this. BCIT's Division 28 standard limits a detection circuit to "80% of maximum number of detectors allowed by control panel manufacturer for that circuit", so a circuit drawn at 100 per cent of rating has already broken that spec.

Voltage at the last device, which nobody checks until the horns sound weak. A circuit can sit inside its current rating and still fail because 60 metres of 14 AWG dropped it below what the last appliance needs.

Fail any of the three and say so in writing, before the wire goes in.

End of line devices and circuit class

An end of line device, usually a resistor, is how a Class B circuit is supervised: the panel pushes a small current out through the circuit and back through that resistor, and a cut conductor stops it and raises a trouble. That is supervision in one sentence, and it is why the resistor belongs at the last device and nowhere else.

So the far end tells you the class. A circuit ending at a resistor after the last device is Class B: one path out, and a break kills everything downstream. A circuit returning to a separate pair of terminals at the panel is Class A: two paths, and a single break is annunciated while the circuit keeps working from both directions.

That is a fast error check. A run labelled Class A but drawn ending at a resistor with no return means one of the two is wrong. The resistor value comes from the panel manufacturer, not from habit.

Annunciators, transponders and remote power supplies

An annunciator shows status: lamps or a display, sometimes controls, and no circuits of its own leaving it. The University of Toronto's fire alarm design standard requires the main control panel or central alarm and control facility to be "located at the designated fire department response point and used as the main annunciator", so its position on the sheet is a code driven decision.

A transponder is a remote piece of the panel. It sits on the signalling line circuit, takes its own 120 V branch circuit, usually carries its own batteries, and has circuits leaving it. On the riser it looks like a small second panel partway up the building, and its circuit ratings are frequently smaller than the main panel's. That gap is where loading errors hide.

A remote power supply is a booster with no intelligence: it takes a trigger and repeats it onto locally powered notification circuits. If notification circuits leave a box that is not on the signalling line circuit, that is what you are looking at. Each one adds a branch circuit, batteries and a battery calculation.

Interfaces are the part that gets underestimated

Sprinkler flow and valve tamper switches arrive as monitor modules or as points on an initiating circuit. Flow is an alarm. Tamper is a supervisory condition. If you are shaky on that distinction, read alarm, supervisory and trouble signals first, because a good share of matrix errors are really signal type errors.

Elevator recall, HVAC shutdown, door holders and magnetic locks appear as control modules or dry contact relays. These are ancillary devices, and the fire alarm system's job is only to provide the signal. What the elevator does with it is set by the elevator code and the elevator contractor, and we cover the Ontario side in elevator recall in Ontario.

The input output matrix

The input output matrix is a table. Rows are inputs, meaning anything that can put the system into an off normal state. Columns are outputs, meaning anything the system can make happen. A mark where they meet says that input must produce that output, and reading one row across gives the complete sequence of operation for it. Prose hides gaps. A table makes an empty row obvious.

Four things to check as you read:

Signal type. Alarm, supervisory or trouble? A tamper row with the alarm column ticked is an error, not a preference.

Stage. On a two stage system, alert or alarm? An unacknowledged alert escalates on its own, and the Ontario Building Code sets that at five minutes. We are citing an unofficial online reproduction of Article 3.2.4.4 of the 2012 Ontario Building Code for that figure, so check it against the current O. Reg. 163/24 text. Which buildings get which is covered in single stage versus two stage systems.

Scope of notification. Building wide, or floor of origin plus the floors above and below? Zone by zone notification changes the wiring, not just the programming.

Consistency with the riser. Does every relay have a column, and every column a device to drive it?

A worked example

The building below is invented, and the numbers are chosen to teach.

Cedar Line Court is a fictional four storey residential building: twelve suites per floor, one elevator, one air handling unit, fully sprinklered, two stage.

The riser, in words:

• FACU-1, the control unit, is in the level 1 service room, fed 120 V from panel LP-1 circuit 3, red, lockable on, marked as fire alarm. ANN-1, a remote annunciator, is in the level 1 lobby at the fire department response point.
• SLC-1 is Class A: out of FACU-1, up through levels 1 to 4, and back to the panel's return terminals. Fifty seven addresses used of the 159 the data sheet allows.
• NAC-1 and NAC-2 leave FACU-1, Class B, rated 2.0 A each, serving levels 1 and 2, each ending at an end of line resistor.
• TP-1, a transponder, is in the level 3 electrical room on SLC-1, with its own branch circuit and batteries. NAC-3 and NAC-4 leave TP-1, Class B, rated 1.5 A each, serving levels 3 and 4.
• Each floor carries twelve in suite audible devices at 0.12 A and two corridor horn and strobe units at 0.18 A.

Do the arithmetic before reading on. Twelve at 0.12 A is 1.44 A, two at 0.18 A is 0.36 A, so each floor draws 1.80 A. Levels 1 and 2 fit inside 2.0 A with about ten per cent to spare, thin but legal. Levels 3 and 4 are fed from a transponder whose circuits are rated 1.5 A, so they are drawn 0.3 A over. That is an RFI, and it is the whole reason to read a riser with a calculator open.

The matrix:

Now walk one input through. A corridor smoke detector on level 2 operates.

1. The detector reports its address on SLC-1. FACU-1 identifies it individually, because it is addressable, and logs it with a timestamp.
2. FACU-1 and ANN-1 both light zone 2, so the fire department arriving at the response point sees level 2 without opening the service room.
3. Row two reads across. The alert stage sounds building wide on all four notification circuits, NAC-1 and NAC-2 from the panel, NAC-3 and NAC-4 from TP-1. All 56 audible devices operate at once, a total alarm load of 7.2 A before the panel, annunciator and modules. That number belongs in the battery calculation.
4. Door holders on all four floors release and the stair vestibule magnetic locks drop. Those are control modules on SLC-1, each drawn on the riser.
5. The alarm is transmitted to the monitoring station.
6. Nothing happens to the elevator. The recall cell is blank, because here only the elevator lobby and machine room detectors recall the car. Plenty of consultants recall on any common alarm instead, so this is the kind of cell you confirm rather than assume.
7. AHU-1 keeps running. Only the duct detector row shuts it down here. Practice varies, so this is a question for the consultant rather than a defect.
8. Nobody acknowledges. Five minutes later the panel escalates on its own, and the alarm stage sounds on all four circuits with the alarm pattern rather than the alert pattern.

Every one of those eight steps is testable, and a verifier will test them. Walk the level 1 lobby detector next and notice the recall cell says alternate level: sending the car to a lobby filling with smoke is the failure recall logic exists to prevent, which is why lobby detectors are split by floor rather than lumped together.

What to check before you pull wire

Put the riser, the matrix, the floor plans and the specification side by side and hunt for four things: devices on the plans that are not on the riser and the reverse, relays on the riser with no matrix row or column, matrix outputs with no device to drive them, and circuit loading that does not add up. Counting devices across four documents is boring, and it is the highest value hour you will spend on the job.

When documents genuinely contradict each other, the contract decides. Under General Condition 1.1.5 of the standard CCDC 2 stipulated price contract, priority runs from the agreement down through the general conditions, Division 01, the technical specifications, the schedules, and last, the drawings. Specifications outrank drawings, later dated documents outrank earlier ones of the same type, written dimensions outrank scaled ones, and notes outrank the graphic. Check which edition of CCDC 2 your project uses and whether the supplementary conditions changed that order, because they often do.

None of it overrides the code. The Building Code and the applicable CAN/ULC standards are the floor. A specification can require more. It cannot let you do less.

Why this lands on you at verification

The verifier working to CAN/ULC-S537 is not inventing a test plan. They are testing the system against its design documents, which means against your riser and your matrix. In the same 2023 UL presentation, the S537 scope was described as inspection and test procedures "for the purpose of verifying that the fire alarm system is installed in conformance with the design", and for addressable systems a printout of the input to output software correlation report was said to form part of the verification documentation.

That correlation report is the panel's own version of the matrix. If the programming and the consultant's matrix disagree, the difference gets printed and handed to the person signing the certificate, and a cell nobody could build becomes a deficiency with your company's name beside it. Our guide to what S537 verification involves covers the process end to end.

What is not settled, and what to ask the AHJ

Symbols are not standardised. We could not find any Canadian code, standard or regulation mandating a fire alarm drawing symbol set. There is a well known American symbol standard, and it is not adopted by Canadian codes, so it is not a basis for anything here. Treat every legend as project specific and query ambiguous symbols in writing.

Whether a duct smoke detector alarms or gives a supervisory signal changes with occupancy and code edition. Confirm it for your project rather than carrying the last job's answer over.

Whether elevator recall follows lobby detectors only or any common alarm, and whether magnetic locks release at alert or at alarm, both vary between designers. Both arrangements are in service. Get the answer in writing.

Edition adoption varies by province. CAN/ULC-S524:2019 is the current installation standard, but which edition applies depends on what your provincial building code has adopted.

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