MI Fire Alarm cheat sheet

A conventional (zone) system reports an alarm by zone, not by individual device; the panel identifies the zone, and devices within a zone are not individually annunciated.

An addressable system assigns each device a unique address, so the panel annunciates the specific device in alarm, trouble, or supervisory condition.

Initiating devices include manual pull stations, smoke detectors, heat detectors, duct detectors, and waterflow switches; notification appliances include horns, strobes, chimes, and speakers.

A supervisory signal indicates an off-normal condition of a system or protected equipment (valve closed, low air pressure); a trouble signal indicates a fault in the system itself.

Alarm, supervisory, and trouble signals are distinct signal types and must be visually and audibly distinguishable at the control unit.

Class A initiating device circuits and notification appliance circuits continue to operate with a single open or ground fault; Class B circuits do not.

A waterflow switch on a sprinkler system is an initiating device; a tamper switch on a control valve is a supervisory device.

Smoke detectors are generally cross-zoned or verified to reduce nuisance alarms; heat detectors respond to fixed temperature, rate of rise, or both.

NFPA 72 is the National Fire Alarm and Signaling Code; NFPA 70 (NEC) governs electrical installation, and NFPA 101 governs life safety.

NFPA 72 requires a smoke detector within 21 ft of travel along the ceiling to a wall for level ceilings, measured horizontally, unless a specific exception applies.

Smoke detectors are generally spaced at 30 ft (900 sq ft per detector) for smooth ceilings; heat detectors at 50 ft spacing (2500 sq ft) for the standard listing.

On a peaked or sloped ceiling, detectors are placed near the peak but at least 4 in. down from the peak on the slope.

Detectors must be at least 3 ft from supply or return air diffusers to avoid dilution of smoke.

Manual pull stations must be mounted between 42 in. and 48 in. above the finished floor, measured to the operating handle.

Notification appliance circuits must provide a sound level at least 15 dBA above ambient, or 105 dBA where ambient exceeds 105 dBA, measured 5 ft above the floor.

In sleeping areas, sounders must produce at least 75 dBA at the pillow, or 15 dBA above ambient, whichever is greater.

Ohm's law: V = I × R, where V is volts, I is amperes, and R is ohms.

Power: P = V × I = I²R = V²/R, where P is watts.

Series circuit: total resistance is the sum of individual resistances; current is the same through all components.

Parallel circuit: total resistance is 1/RT = 1/R1 + 1/R2 + ...; voltage is the same across all branches.

End-of-line (EOL) resistor value is chosen to match the panel's supervision requirement; a shorted or open EOL causes a trouble condition.

A ground fault is an unintentional connection between a conductor and ground; it is detected by the panel's ground-fault monitoring and annunciated as a trouble.

Supervised circuits use a small supervisory current to detect opens, shorts, and grounds on the wiring between the panel and field devices.

Battery standby capacity is calculated as total standby current times required hours, plus alarm current times alarm duration, with a derating factor applied.

NFPA 72 requires acceptance testing before a system is placed in service, and periodic inspection, testing, and maintenance thereafter.

Smoke detectors are tested annually (functional test with smoke or manufacturer's listed method); heat detectors are tested annually or per manufacturer.

Manual pull stations are tested annually by operating the mechanism and verifying alarm annunciation.

Notification appliances are tested annually for audibility and visibility; batteries are inspected quarterly and tested annually.

Waterflow switches are tested semiannually (or quarterly where supervised) by opening the inspector's test valve; tamper switches are tested semiannually.

Control equipment is inspected monthly or quarterly depending on system type; a record of all tests and inspections must be maintained.

A test of a smoke detector using canned smoke verifies the detector's response; a magnet test verifies only the detector's electronic circuit, not the sensing chamber.

After any modification, repair, or replacement of a device, the affected portion of the system must be retested before returning to service.

A duct smoke detector is used to detect smoke in HVAC ducts and to initiate shutdown of air-handling equipment; it is not a substitute for area detection.

Elevator recall is a fire alarm function that, upon alarm, sends elevators to a designated landing and disables normal operation.

A sprinkler system's alarm check valve, when it operates, activates a waterflow switch that sends an alarm signal to the panel.

A trouble signal must sound at the control unit within a specified time (often 200 seconds) after a fault occurs, depending on the system type.

Notification appliance circuits may be Class A or Class B; Class A returns the circuit to the panel, allowing operation with a single fault.

A zone is a defined area of the protected premises; addressable systems may group devices into logical zones for annunciation and response.

The alarm silence function silences notification appliances but does not reset the system; the reset function clears the alarm condition after the initiating device returns to normal.

A short circuit is a low-resistance path that bypasses the normal load, causing excessive current; it is detected as a trouble on supervised circuits.

An open circuit is a break in the conductor path; on a supervised circuit it is detected as a trouble condition.

Voltage drop along a circuit is calculated as Vdrop = I × Rconductor, where Rconductor depends on wire gauge and length.

Wire size is selected based on current-carrying capacity and voltage drop; 14 AWG is rated 15 A, 12 AWG is rated 20 A for typical branch circuits.

A transformer steps voltage up or down according to the turns ratio; power is approximately conserved (minus losses).

Battery charging circuits maintain standby batteries at a float voltage; a charger failure is annunciated as a trouble.

A relay is an electrically operated switch used to control circuits; a supervised relay output can be monitored for fault conditions.

NFPA 72 requires that a fire alarm system be installed in accordance with the manufacturer's published instructions and the applicable code edition.

Detectors must not be installed within 3 ft of the supply or return air diffuser, and must be at least 4 in. from the wall on a sidewall mount.

In corridors, smoke detectors are spaced per the ceiling height and configuration; the 30 ft spacing rule applies to smooth, level ceilings.

A fire alarm control unit must be located in an area that is accessible and not subject to physical damage; it must be annunciated at a constantly attended location if required.

The authority having jurisdiction (AHJ) approves the installation, witnesses acceptance testing, and may require additional devices or testing.

Plans and specifications must be submitted to the AHJ for review before installation begins in most jurisdictions.

Record drawings (as-builts) must be maintained and updated to reflect the installed system.

Inspection is a visual examination; testing is the functional operation of a device or system; maintenance is the repair or replacement of components.

The annual test of a fire alarm system includes testing initiating devices, notification appliances, and control functions.

Sensitivity testing of smoke detectors is required to verify the detector is within its listed sensitivity range; it may be performed with a calibrated test instrument.

A detector that fails sensitivity testing must be cleaned, recalibrated, or replaced.

Records of inspection, testing, and maintenance must be retained and made available to the AHJ.

Testing must not leave the system impaired; if a system is taken out of service, the AHJ and occupants must be notified and a fire watch implemented where required.

A smoke detector's sensitivity can drift due to dirt accumulation; the detector's built-in drift compensation may delay a trouble indication until the drift exceeds the compensation range.

A fire alarm system's primary power source is typically the building's commercial power; a secondary source (batteries or generator) provides standby power.

The secondary power supply must be capable of operating the system for a specified duration (often 24 hours standby plus 5 minutes alarm) depending on the system type and code edition.

A fire alarm control unit monitors its primary and secondary power sources and annunciates a trouble if either fails.

Addressable devices communicate with the panel over a signaling line circuit (SLC); the SLC is supervised for opens, shorts, and grounds.

A conventional initiating device circuit is supervised by an end-of-line resistor; the panel detects a change in circuit current to identify an alarm.

Notification appliance circuits are supervised and may be Class A or Class B; the circuit must be capable of operating all appliances at their rated voltage.

A fire alarm system may interface with other systems (sprinkler, HVAC, elevator, access control) through relay modules or dedicated interfaces.

A resistor opposes current flow; its value in ohms determines the current for a given voltage.

A capacitor stores energy in an electric field; it opposes changes in voltage and is used for filtering and timing.

A diode allows current in one direction only; it is used for rectification and protection.

Alternating current (AC) reverses direction periodically; direct current (DC) flows in one direction.

The RMS value of a sinusoidal AC voltage is approximately 0.707 times the peak value.

A ground fault circuit interrupter (GFCI) detects a difference between line and neutral current and opens the circuit; it is not a substitute for a fire alarm ground-fault monitor.

Battery capacity is rated in ampere-hours (Ah); the available energy is approximately the Ah rating times the nominal voltage.

NFPA 72 requires that smoke detectors be installed on the ceiling or, if wall-mounted, between 4 in. and 12 in. from the ceiling.

Detectors must be at least 3 ft from the supply or return air diffuser to avoid dilution of smoke by air movement.

On a sloped ceiling, detectors are placed within 3 ft of the peak, measured horizontally, but at least 4 in. down from the peak.

Manual pull stations must be located within 5 ft of the exit door and mounted 42 in. to 48 in. above the floor.

Notification appliances must be audible throughout the protected area; in sleeping areas, the sound level at the pillow must be at least 75 dBA.

Strobes must be visible from all points in the protected area; the candela rating and mounting height determine coverage.

The AHJ has the authority to interpret the code and to require additional fire alarm devices or testing.

Smoke detectors are tested annually; the test method must verify the detector's ability to respond to smoke, not just its electronic circuit.

Heat detectors are tested annually with a listed heat source or per the manufacturer's instructions.

Manual pull stations are tested annually by operating the mechanism and verifying the alarm signal.

Notification appliances are tested annually for audibility, visibility, and correct operation.

Batteries are inspected quarterly and tested annually; a load test verifies the battery's ability to supply the required current.

Waterflow switches are tested semiannually by opening the inspector's test valve; tamper switches are tested semiannually.

A record of all inspection, testing, and maintenance activities must be maintained and made available to the AHJ.