Fire Alarm Wiring Guide
Purpose
This document covers the wiring requirements for fire alarm systems — cable types, routing rules, conventional zone wiring, addressable loop wiring, and sounder circuit wiring. Fire alarm wiring has specific requirements that differ from standard electrical or security alarm wiring.
Cable Types
Fire-Rated Cable — The Fundamental Requirement
All fire alarm detection wiring must use fire-rated cable. Standard twin-and-earth or unscreened alarm cable is not acceptable.
Why: In a fire, the alarm cable must continue to carry the signal long enough for the building to evacuate. Standard cable melts early in a fire — fire-rated cable maintains circuit integrity under fire conditions.
UK standard: Fire-rated cable to BS 7629-1 — typically referred to as FP200 Gold or equivalent. Maintains circuit integrity at 930°C for a minimum of 30 minutes.
| Type | Description | Use |
|---|---|---|
| FP200 Gold 1.5mm² | 2-core + earth, fire rated | Detection circuits (most common) |
| FP200 Gold screened | Screened, fire rated | Where screening is required |
| MICC | Mineral insulated copper | High-risk areas, extreme fire-resistance |
Never use standard unscreened alarm cable for fire alarm detection circuits.
Cable Identification
FP200 Gold is red — the standard colour for fire alarm circuits in the UK. This aids identification during maintenance and fault-finding.
Cable Routing
Separation from Other Services
- Minimum 50mm separation from mains power cables
- Minimum 50mm separation from data cables (Cat5/6)
- Where cables must cross mains: cross at 90°
Mechanical Protection
Expose areas (plant rooms, external routes, areas of mechanical risk): protect with conduit or trunking.
Route Selection
Avoid routing through:
- High-temperature areas (near boilers, flues, ovens)
- High fire-risk areas where cable could be destroyed before it signals
Where cables must run through high-risk areas: use MICC cable or provide additional mechanical protection.
Conventional Zone Wiring
Detectors and call points are wired in circuits (zones). The circuit starts at the panel, runs through each device, and terminates with an EOL (End-of-Line) resistor at the final device.
PANEL → Detector 1 → Detector 2 → Detector 3 → [EOL Resistor]
The EOL resistor allows the panel to distinguish between:
- Normal: Circuit complete with resistor — panel reads normal resistance
- Alarm: Device activated — circuit changes state
- Fault: Cable break — panel reads open circuit
EOL resistor value: Set by the panel manufacturer — typically 4.7kΩ or as specified. Must match what the panel expects.
Connecting Conventional Detectors
- L and L terminals on the detector base: zone circuit in and out (loop through)
- Bases without a detector head fitted will cause a zone fault — fit all bases before powering up
Call Points on Conventional Zones
MCPs are wired into the zone circuit. They contain a normally-closed contact that opens when activated — registering as an alarm on the zone.
Addressable Loop Wiring
All devices on an addressable loop are wired in a single circuit carrying both power and data. The panel communicates with each device individually to read status and send commands.
Class B Loop (Spur)
The loop cable runs from the panel to each device in sequence, terminating at the last device.
Limitation: A break anywhere isolates all devices beyond the break.
Class A Loop (Redundant)
The loop cable runs from the panel through all devices and returns to the panel at a second connection point — forming a complete ring.
Advantage: A single cable break does not isolate any device — data reaches every device from the other direction. Required on most commercial installations.
Loop Cable Specification
Use the cable type specified by the panel manufacturer. C-Tec ZFP typically requires 1.5mm² fire-rated screened cable. Connect the screen at the panel end only (one end grounded to avoid ground loops).
Maximum loop resistance: Follow the manufacturer's specification — typically around 40Ω total for a Class A loop.
Sounder and Beacon Wiring
Sounders and beacons are wired on separate sounder circuits from the panel — not on the detection loop.
Conventional Sounder Circuits
Wired as a positive and negative pair from the panel. The panel applies voltage to activate.
EOL device: A resistor or diode is fitted at the end of the sounder circuit so the panel can supervise the wiring, detecting open circuit faults even when sounders are not active.
Sounder Polarity
Sounders are polarity-sensitive — incorrect polarity prevents operation.
- + = positive (red)
- − = negative (black/blue)
Panel Wiring — Connections at the Panel
- Zone/loop terminals labelled correctly and wired to the correct circuit
- Sounder circuits on the correct terminals
- Mains input connected correctly (live, neutral, earth)
- Battery connected with correct polarity
- Any auxiliary relay outputs connected correctly
All panel wiring must be neat, identified, and mechanically secure. Fire alarm panels are inspected during service visits — poor wiring creates doubt about the quality of the whole installation.