CT Fire Alarm cheat sheet

NFPA 72 classifies systems as protected premises (local, auxiliary, remote station, proprietary, central station) and supervising station types; the classification drives transmission and annunciation requirements.

NFPA 72 Chapter 9 covers initiating devices; Chapter 10 covers notification appliances; Chapter 12 covers circuits and pathways; survivability of critical circuits is addressed by pathway Class (A, B, C, D, E, N, X).

Occupancy-specific detection mandates come from NFPA 101 and the locally adopted building code; NFPA 72 itself does not state which occupancies require a fire alarm system.

Class A pathway: circuit continues to operate with a single open or ground fault. Class B: single open fault causes loss of function beyond the fault but does not affect devices ahead of it. Class X: operation continues during a single open, short, or ground fault.

In-building fire emergency voice/alarm communication systems (EVACS) require intelligible voice per NFPA 72 Chapter 18; intelligibility is evaluated at 15 dBA above average ambient or 5 dBA above maximum ambient, whichever is greater, in each occupiable area.

A fire alarm control unit must be listed to ANSI/UL 864; releasing service panels and suppression control units have separate listing criteria (UL 864 releasing, UL 864/UL 2017 combinations).

Documentation required at acceptance includes record of completion, as-built drawings, sequence of operations matrix, battery calculations, and the inspection/testing/maintenance schedule from NFPA 72 Chapter 14.

Detector spacing rules: spot smoke detectors use the 30 ft (9.1 m) smooth-ceiling spacing rule with 21 ft (6.4 m) between detectors on a row and 10.6 ft (3.2 m) from walls, adjusted per NFPA 72 figures for ceiling height and slope.

Primary supply: 120 VAC branch circuit dedicated to the fire alarm system, marked "FIRE ALARM CIRCUIT CONTROL," with circuit disconnecting means accessible only to authorized personnel and protected against accidental disconnection.

Secondary supply: sealed lead-acid or nickel-cadmium batteries sized for 24 hours of standby plus 5 minutes of alarm (or 4 minutes for voice systems), per NFPA 72 Table 10.6.7.2.1.

Battery capacity formula: required Ah = (standby current × standby hours + alarm current × alarm hours) × 1.25 (aging factor); use manufacturer's derating for end-of-life capacity.

Voltage drop on notification circuits: Vdrop = 2 × L × I × R, where L is one-way distance in ft and R is resistance per foot of the conductor; keep end-of-line voltage above the appliance's minimum rated operating voltage.

Ohm's law and power: V = IR; P = VI = I²R = V²/R. A 24 VDC notification appliance drawing 0.5 A dissipates 12 W and presents 48 Ω.

Notification appliance circuits are typically power-limited Class 2 or Class 3; power-limited circuit conductors must be separated from non-power-limited conductors by at least 2 in. (50 mm) or a listed barrier.

Ground fault detection: the control unit must annunciate a ground fault on any conductor of an initiating, notification, or signaling circuit that grounds; a single ground on a Class B circuit may not cause an alarm but must be indicated.

Supervisory current for a 24 VDC conventional zone is typically 4-20 mA through the end-of-line resistor; alarm current is drawn by shorting the zone through a detector or pull station.

Smoke detector types: ionization (better for flaming, fast fires, small particles), photoelectric (better for smoldering fires, larger particles), and combination/multi-criteria (photoelectric plus heat or CO).

Heat detector types: fixed temperature (typically 135°F or 194°F), rate-of-rise (triggers when temperature rises faster than about 15°F per minute), and combination fixed/rate-of-rise.

Duct smoke detectors are required where air-handling systems are rated over 2,000 cfm (0.94 m³/s) to shut down the unit and, where required, to close dampers; sampling tubes must span the full duct width and be oriented per airflow.

Projected-beam smoke detectors have a maximum spacing of 60 ft (18.3 m) between units and 30 ft (9.1 m) from walls; the beam path must be unobstructed and the detector listed for the ceiling height.

Manual pull stations must be located within 5 ft (1.5 m) of each exit door, mounted 42-48 in. (1.07-1.22 m) above the floor, and unobstructed; at least one per required exit.

Spot heat detector spacing on smooth ceilings: 50 ft (15.2 m) for 135°F units, 30 ft (9.1 m) for 194°F units, with the first detector within half the spacing of a wall.

Air-sampling (ASD) systems require pipe network design per manufacturer's listed calculations; a single pipe run must not exceed the listed maximum length (commonly 800 ft) and each sampling point must be within the listed sensitivity.

Detector spacing must be reduced by 0.5 ft per 1 ft of ceiling height above 10 ft for smoke detectors, per NFPA 72 figures; for heat detectors, the reduction starts above 10 ft and is steeper.

Audible appliances must produce at least 15 dBA above average ambient or 5 dBA above maximum ambient, whichever is greater, measured 5 ft (1.5 m) from the floor in each occupiable area.

Public mode audible signals must not exceed 110 dBA at minimum hearing distance; if the ambient exceeds 105 dBA, visible-only notification is permitted where listed.

Visible notification appliances: candela ratings per NFPA 72 Chapter 18 tables; 15 cd minimum for a 20 ft × 20 ft room, increasing with room size and mounting height; wall-mounted units at 80-96 in. above the floor.

Synchronization is required for visible appliances in the same field of view; the control unit or a listed sync module must keep flash cycles in phase within 10 milliseconds.

Strobes must flash at 1-2 Hz (typically 1 Hz); the pulse duration must be at least 0.1 second; the flash rate and intensity must be maintained for the life of the appliance.

Notification appliance circuits (NACs) are typically Class B or Class A supervised circuits; end-of-line resistor supervision must detect open, short, and ground faults.

Voice evacuation systems require intelligible voice messages; the sound pressure level for voice must be at least 15 dBA above ambient but not exceed 110 dBA, and the message must be repeated until acknowledged or the system reset.

Speaker circuit design: use the manufacturer's listed tap settings; total load must not exceed the amplifier's rated output; speaker lines are supervised for opens and shorts and must be Class A or B as designed.

NFPA 72 Chapter 12 pathway Class definitions: Class A, B, C, D, E, N, X; Class A requires a redundant path and continues operation on a single open; Class X continues on a single open, short, or ground fault.

Conductor color coding is not mandated by NFPA 72 but is a common local practice; however, the control unit must have a permanent label identifying the function of each circuit and the color code used.

Plenum-rated cable (CMP) is required in environmental air-handling spaces unless installed in metallic conduit; riser-rated (CMR) cable is used in vertical shafts.

Acceptance testing per NFPA 72 Chapter 14 requires testing 100% of initiating devices, 100% of notification appliances, and all control unit functions; a representative sample is not permitted for new installations.

Inspection/testing/maintenance frequencies: monthly for control unit indicators and batteries under load, quarterly for alarm and supervisory devices, annually for all initiating and notification devices, and every 5 years for sensitivity testing of smoke detectors.

Smoke detector sensitivity must be tested within 1 year of installation and every 5 years thereafter, or per manufacturer's instructions, using a listed test method; the detector must be within its listed sensitivity range.

Ground fault testing: introduce a ground on each supervised circuit and verify annunciation; the ground must not cause an alarm or a trouble on an unrelated circuit.

Documentation: the record of completion must be signed by the installing contractor and the owner's representative; the inspection and testing report must be retained and made available to the authority having jurisdiction.

NFPA 72 Chapter 10 notification appliance requirements include public mode, private mode, and visible-only criteria; the applicable mode depends on occupancy and ambient conditions.

A supervising station must be listed to UL 864 and, where required, UL 827; central station service requires a listed central station and a means of two-way communication.

The authority having jurisdiction (AHJ) approves the installation, the record of completion, and any deviations from the adopted code; the AHJ may accept equivalent protection.

Sequence of operations must be documented and verified at acceptance; it defines which inputs activate which outputs, including HVAC shutdown, door release, and elevator recall.

Elevator recall: smoke detectors in the elevator lobby, machine room, and hoistway pit initiate Phase I recall; a detector in the elevator car initiates Phase II recall; the sequence must be coordinated with the elevator code (ASME A17.1).

Area of refuge communication systems and two-way emergency communication systems are addressed by NFPA 72 Chapter 24 and the building code; they require listed equipment and battery backup.

Initiating device circuits (IDCs) are supervised; conventional zones use an end-of-line resistor; addressable systems use a digital protocol and each device has a unique address and a supervision scheme.

A 24 VDC system with 1 A alarm load and 0.1 A standby load, 24 h standby plus 5 min alarm, requires (0.1 × 24 + 1 × 0.083) × 1.25 = 3.1 Ah minimum battery capacity before derating.

Battery charging: the charger must restore the battery to 85% capacity within 24 hours after a full discharge; the charging voltage for a 24 V lead-acid bank is typically 27.6 V float.

Transformer sizing: the primary supply must be capable of supplying the control unit's standby and alarm loads plus battery recharge current; a dedicated circuit is required.

Conductor ampacity: use NFPA 70 (NEC) Table 310.16 for copper conductors; fire alarm circuits are typically #14 to #12 AWG, and voltage drop must be calculated, not assumed.

Surge protection: listed transient voltage surge suppressors are recommended on AC and communication lines; the suppressor must not impair supervision.

Isolation: addressable systems use isolator modules to limit the effect of a short circuit on a loop; the isolator opens the segment and the control unit annunciates the fault.

Power-limited circuit calculations: the total load on a power-limited circuit must not exceed the listed power limitations of the control unit; the manufacturer's installation instructions provide the maximum load.

Smoke detector placement: at least 3 ft (0.9 m) from air supply diffusers, 3 ft from bathroom doors, and not in dead air spaces; on sloped ceilings, the detector must be within the listed distance of the peak.

Beam detectors and air-sampling systems require specific design per the manufacturer's listed instructions; the design must be documented and approved by the AHJ.

Heat detector spacing on sloped ceilings: the first detector must be within the listed distance of the peak; the spacing is reduced per the slope.

Duct detector placement: sampling tubes must be installed in the return air duct, upstream of the filters and before any branch connections, and the detector must be accessible for service.

Manual pull stations must be listed and marked; they must be mounted so the operating handle is 42-48 in. above the floor and within 5 ft of the exit door.

Detector testing: use listed test smoke or heat; do not use a lighter or open flame; the test must verify alarm initiation and annunciation at the control unit.

Addressable devices: each device must be programmed with a unique address; the address must match the as-built drawings and the sequence of operations.

Detector spacing on a smooth ceiling: the 30 ft spacing rule applies to smoke detectors; the area covered by a single detector is approximately 900 ft², and the distance to walls is 10.6 ft.

Visible appliance mounting: wall-mounted strobes at 80-96 in. above the floor; ceiling-mounted at the center of the room; the candela rating must be selected from the NFPA 72 tables based on room size and mounting height.

Audible appliance mounting: at least 6 in. (150 mm) below the ceiling, or per the manufacturer's listed instructions; the sound must be measured at 5 ft above the floor.

Notification appliance circuit voltage drop must be calculated for the worst-case appliance; the end-of-line voltage must be at least the appliance's minimum rated voltage.

Synchronization modules must be listed and installed per the manufacturer's instructions; the sync module must be supervised and powered from the control unit.

Speaker circuits: the total speaker load must not exceed the amplifier's rated output; the tap settings must be recorded on the as-built drawings.

Voice intelligibility: the common intelligibility scale (CIS) must be at least 0.45, or the speech transmission index (STI) at least 0.45, in each occupiable area.

Notification appliance testing: verify each appliance operates at its rated candela and dBA; the test must be recorded on the inspection report.

Conductor installation: fire alarm cables must be supported at intervals not exceeding 10 ft (3 m) and within 12 in. (300 mm) of boxes; cables must not be installed in raceways with non-fire-alarm conductors unless separated by a barrier.

Boxes and enclosures: use listed boxes; the box must be accessible; the cover must be marked with the circuit function.

Grounding: the control unit must be grounded per NFPA 70 Article 250; the grounding conductor must be sized per the overcurrent protection.

Acceptance test documentation: the record of completion must include the date, the names of the tester and the owner's representative, and the results of each test.

Periodic testing: monthly for control unit and battery, quarterly for alarm and supervisory devices, annually for all initiating and notification devices, and every 5 years for smoke detector sensitivity.

Testing of addressable systems: verify each device's address, the annunciation at the control unit, and the correct sequence of operations for each input.

Battery testing: test under load for the calculated standby and alarm periods; the battery must maintain at least 85% of its rated capacity.

NFPA 72 Chapter 14 inspection, testing, and maintenance (ITM) requirements apply to all systems; the ITM schedule must be documented and followed.

The record of completion must be updated whenever the system is modified; the as-built drawings must reflect the current configuration.

The AHJ may require a pre-acceptance test and a final acceptance test; the contractor must provide the test plan and the record of completion.

System modifications: any change to the sequence of operations or the device layout requires a new record of completion and, where required, a new acceptance test.

Fire alarm system monitoring: central station service requires a listed central station and a means of two-way communication; the monitoring agreement must be documented.

The building code (e.g., IBC) determines the required fire alarm system features; NFPA 72 provides the installation and performance requirements.

Battery replacement: sealed lead-acid batteries must be replaced every 4-5 years or when they fail a load test; the replacement must be the same type and rating as the original.

Battery testing: the battery must be tested under load for the calculated standby and alarm periods; the test must be recorded.

Power supply supervision: the control unit must annunciate a loss of AC power, a low battery, and a battery charger failure.

Transformer: the primary supply must be a dedicated circuit; the transformer must be listed for fire alarm use and sized for the load.

Voltage drop: use the manufacturer's voltage drop calculator or the formula Vdrop = 2 × L × I × R; the end-of-line voltage must be at least the appliance's minimum rated voltage.

Power-limited circuits: the total load must not exceed the listed power limitations; the manufacturer's installation instructions provide the maximum load.

Smoke detector testing: use listed test smoke; verify alarm initiation and annunciation; the detector must be within its listed sensitivity range.

Heat detector testing: use a listed heat source; verify alarm initiation and annunciation; the detector must be within its listed sensitivity range.

Manual pull station testing: operate the handle; verify alarm initiation and annunciation; the station must be reset and the glass rod replaced.

Duct detector testing: use listed test smoke; verify alarm initiation, annunciation, and HVAC shutdown.

Addressable device testing: verify each device's address and the correct sequence of operations.

Audible appliance testing: measure the sound pressure level at 5 ft above the floor; verify at least 15 dBA above ambient or 5 dBA above maximum ambient.

Visible appliance testing: verify each appliance operates at its rated candela; verify synchronization.

Voice system testing: verify intelligibility; the CIS or STI must be at least 0.45 in each occupiable area.

Speaker circuit testing: verify the total load does not exceed the amplifier's rated output; verify supervision.

Cable installation: support at intervals not exceeding 10 ft and within 12 in. of boxes; use listed cable for the environment.

Boxes and enclosures: use listed boxes; the box must be accessible; the cover must be marked with the circuit function.

Grounding: the control unit must be grounded per NFPA 70 Article 250.

Acceptance test documentation: the record of completion must include the date, the names of the tester and the owner's representative, and the results of each test.

Periodic testing: monthly for control unit and battery, quarterly for alarm and supervisory devices, annually for all initiating and notification devices, and every 5 years for smoke detector sensitivity.