Field reference for fire alarm and life safety technicians. 11 entries, taken from the LoopWatt app.
Reference notes from LoopWatt, the offline field toolkit for fire alarm and life safety technicians. It works with no cell signal, because the sites do not have any.
Get LoopWatt on the App StoreFire alarm wiring uses two conductors with no dedicated ground. When one conductor finds an unintended path to a grounded surface (conduit, back box, structural steel), the panel reports it immediately.
Water ingress at a field device, very often a ceiling mounted smoke or heat detector
Pinched or skinned conductor at a back box or fitting
Screw driven through a cable
Failed device with internal leakage to its mounting
Moisture in exterior or underground junction boxes
Disconnect circuits from the fire alarm control panel one at a time; if the trouble clears, the fault is in that circuit and not the panel
Split the faulted circuit at a midpoint device and see which half holds the fault; repeat to localize
Use an ohmmeter from each conductor to ground with the circuit dead; a low reading marks the faulted conductor
Use an insulation resistance tester at low voltage on a fully disconnected circuit to find high resistance leakage; disconnect all devices first
Check recent roof or plumbing leaks and recently worked areas first
Panel manual; NFPA 72 Chapter 12 circuit classes
A break in the circuit: the panel supervision current cannot complete its path, so the panel shows an open or a missing device trouble.
Loose connection at a device terminal
Faulty or removed device
Damaged or cut cable
Missing or failed end of line resistor
Broken conductor inside insulation at a stress point
Check the panel display for the zone or address range affected
Verify the end of line resistor is present and the right value
Measure loop resistance from the panel end with the EOL shorted at the far end; an open reads infinite
Split the circuit at a midpoint and test each half
Wiggle test suspect terminations; opens are often intermittent at loose screws
Panel manual; Class A vs Class B behavior differs
Conductor to conductor contact. On a conventional initiating zone a short reads as an alarm; on a notification circuit or signaling line circuit it reads as a trouble and may shut the circuit down.
Crushed or stapled cable
Wire strands touching at a device terminal
Failed device
Water in a junction box bridging terminals
Disconnect the circuit at the panel and measure conductor to conductor resistance with devices in place; compare to the expected EOL value
A reading far below the EOL value indicates a short; split the circuit to localize
On SLC loops, isolator modules limit how much of the loop a short takes down; the devices that dropped out point at the shorted segment
Panel manual
The SLC is the communication highway to the panel. Trouble means an open, a short, a device failing to respond to poll, or electrical noise corrupting communication.
Open or short on the loop
Device failing to answer its poll (failed electronics, wrong address, duplicate address)
Electrical noise from VFDs, ballasts, or parallel power runs
Too much loop resistance or capacitance for the loop driver
Water damaged device pulling the loop down intermittently
Read the panel event history: which addresses fail and in what order; a contiguous group points at a wiring segment
Check for duplicate addresses after any device replacement
Measure loop resistance and verify against the panel maximum
Separate SLC conductors from power conductors; check for shared raceway with noisy loads
Use the panel diagnostics (device response quality readings) where the brand provides them
Panel manual; NFPA 72 Chapter 12
Primary power failed or was turned off. The system runs on batteries and reports the loss; delayed transmission to the supervising station is normal by design.
Breaker turned off or tripped, often mislabeled
Utility outage
Failed panel power supply
Dedicated circuit worked on by other trades
Find the dedicated branch circuit; it must be marked and mechanically protected against casual switching
Verify voltage at the panel primary terminals
If the breaker trips again, look for a shorted power supply or field wiring on auxiliary power
NFPA 72 10.6.5; NEC 760.41 and 760.121 branch circuit rules
Battery voltage below threshold, failed charger, or batteries past service life.
Batteries past their service life (typically 3 to 5 years)
Charger failure or blown charger fuse
Undersized batteries for added load
Loose or corroded battery connections
One shorted cell dragging the pair down
Measure float voltage across the set (about 27.3 V for a 24 V system) and each battery separately
Check the install date marking; replace in pairs, never mix old and new
Run the battery calculation after any device additions
Load test per the panel manual; a battery can float fine and still fail under load
Table 14.4.3.2 battery tests; 10.6.7 capacity
Open, short, or overload on a NAC. The panel supervises the circuit through the end of line resistor with reversed polarity in standby.
Missing or wrong EOL resistor
Open at an appliance terminal (in and out wiring not landed on separate terminals)
Shorted appliance or crushed cable
Overload: too many appliances for the circuit rating
Non listed device on the circuit
Verify the EOL value against the panel manual
Measure circuit resistance at the panel with the circuit disconnected
Confirm every appliance is wired in and out on the correct terminals, no pigtails bridging supervision
Add up appliance currents and compare to the circuit rating; run the voltage drop calculation
Panel manual; NFPA 72 Chapter 18
An addressable point the panel expects does not answer, or a device answers at an address the program does not expect.
Device removed and not replaced (painting, remodeling)
Wrong address set after a replacement
Program not updated after system changes
Two devices on one address
Compare the panel point list against the as built device inventory
Re address the replacement device to match the program, or update the program with the designer of record
Walk the area served by the missing address; look for fresh paint, new walls, or missing detector heads
Panel manual; program changes may require re acceptance testing per 14.4.1
Dust and contamination shift a smoke detector's operating point. Modern panels report a dirty or almost dirty condition before it becomes a nuisance alarm source.
Dust accumulation, construction activity without protective covers
Kitchen, shop, or garage environments
Insects inside the chamber
Age; chamber contamination is cumulative
Read the sensitivity or percent obscuration report from the panel where supported; that satisfies the sensitivity test requirement when in range
Clean or replace the detector head per manufacturer instructions
Devices outside their listed range must be cleaned and retested or replaced
Cover detectors during dusty work and remove covers after; a covered detector cannot see smoke
14.4.4.3 sensitivity testing; manufacturer cleaning instructions
The path to the supervising station failed: phone line, cellular, IP, or radio.
POTS line removed or migrated to VoIP without notice
Cellular sunset or antenna problem
Building network change: new firewall, new IP scheme
Failed communicator or blown fuse
Account changes at the monitoring company
Send a manual test signal and confirm receipt with the monitoring company
Check signal strength indicators on cellular units
For IP paths, verify the drop is live and the communicator's destination is reachable
Confirm the account number and phone numbers with the central station
NFPA 72 Chapter 26 transmission technologies
Three distinct signal classes that demand different responses.
ALARM: fire is indicated; devices such as smoke detectors, pull stations, waterflow. Requires immediate evacuation response and dispatch
SUPERVISORY: a fire protection system is off normal but there is no fire: valve tamper, low air pressure on a dry system, duct detector on some designs, fire pump conditions. Requires investigation and restoration
TROUBLE: the fire alarm system itself has a fault: opens, grounds, power or communicator failure. Requires service
A valve tamper must annunciate as supervisory, not alarm and not trouble; mixing these classes is a common programming deficiency
Verify each initiating device type annunciates in its correct class during acceptance and annual testing
Check that supervisory signals are distinct in tone and display from alarms at the panel and the annunciator
NFPA 72 10.7 and 10.8 signal priority and distinction
Reference notes from LoopWatt, the offline field toolkit for fire alarm and life safety technicians. It works with no cell signal, because the sites do not have any.
Get LoopWatt on the App StoreThese notes are a field aid, not a substitute for the governing codes, the stamped drawings, the authority having jurisdiction, or manufacturer manuals. Verify against the current documentation for your installed equipment.