Fire Alarm System Components and Devices
This domain tests your ability to trace a signal from initiation to notification and to select the right component for each function. You should be able to distinguish conventional from addressable architecture, identify initiating device circuits (IDCs) and notification appliance circuits (NACs), and explain the role of power supplies, isolators, relay modules, annunciators, and the communicator.
Core concepts
- The fire alarm control panel (FACP) supervises IDCs, NACs, and internal power; addressable panels supervise individual devices on a signaling line circuit (SLC).
- Two-wire smoke detectors receive power from the IDC; four-wire detectors need separate 24 VDC power and a power-supervision relay.
- NACs are power-limited or non-power-limited circuits that drive horns, strobes, and speakers; voltage drop must be calculated at the end device.
- Addressable isolators limit the effect of a short on an SLC; relay modules control fan shutdown, door release, and elevator recall.
- Remote annunciators and communicators must be supervised and listed for the application.
Worked example
A 60-device addressable SLC serves two floors through one riser. A single short at a floor device could disable the entire loop if no isolators are provided. Placing isolators at each floor separation limits the fault to the affected floor segment and preserves the rest of the loop. The reasoning is that isolators are fault-isolation devices, not surge protectors, and their placement follows circuit topology.
Traps
- Mixing two-wire and four-wire detector wiring without power supervision.
- Forgetting end-of-line resistor placement and supervision.
- Using a relay output as a NAC instead of a listed notification circuit.
- Ignoring NAC voltage drop on long runs.
- Omitting isolators on addressable loops where required by design.