Fire Alarm Panel Integration with KNX: EN 54, Dry Contacts and Relay Logic

Fire alarm panel types

Two fundamentally different panel architectures are used in commercial and residential buildings. Understanding the difference determines how the panel communicates zone status and how many relay outputs are available for KNX integration.

For any commercial KNX integration project, specify an analogue-addressable panel. The device-level identification gives the cause-and-effect logic the precision it needs — a single detector on floor 3 can trigger a different set of KNX actions than a general building-wide alarm. Conventional panels cannot provide this granularity.

Integration principle: dry contact to KNX binary input

The standard integration path between a fire alarm panel and KNX is via volt-free (dry-contact) relay outputs on the fire panel side, read by a KNX binary input module. This architecture keeps the fire system completely isolated from the KNX bus — the fire panel's certified operation is never dependent on KNX, and a KNX failure cannot affect fire detection.

Fire alarm panel (EN 54-2 certified)
    │
    │ Volt-free relay output (dry contact — NO/NC/COM)
    │ Fire-rated cable: EN 50200 FE180/E90 or FPLR
    │
    ▼
Galvanic isolation relay or opto-isolated interface
  Phoenix Contact 2906842 or equivalent dry-contact module
    │
    │ Standard LSZH cable — KNX side only
    │
    ▼
KNX binary input module
  MDT STC-0416.02  (4-channel, DIN rail 2TE)
  Hager TXI616A    (16-channel, DIN rail 4TE)
    │
    │ KNX TP bus
    │
    ▼
KNX group address → KNX actuator action
  Lighting: all circuits 100%
  Lifts: recall to ground, lock out-of-service
  HVAC: fans off, dampers close
  Door holders: 24V cut, doors close
  Visualisation: fire alarm screen activates
  Audio: evacuation message plays

The KNX binary input module converts the contact closure (0V = open, 24V = closed, or configured for volt-free detection) into a KNX telegram on the group address. In ETS6, configure the binary input for contact type (NO or NC), telegram type (DPT 1.001), and set the safety priority flag so no other KNX logic can override the fire telegram.

EN 54-2 required relay outputs

EN 54-2 (Control and Indicating Equipment) mandates three output types on all certified panels. These are the contacts available for KNX integration — each has a distinct purpose and should map to a separate KNX group address.

Use the normally-closed (NC) fault contact with the KNX binary input configured for NC logic — the KNX input detects an open circuit (fault) as an active event. This means a cable break between the fire panel and the KNX input will itself trigger a fault notification, which is the correct fail-safe behaviour.

KNX actions triggered by fire alarm

A general fire alarm relay closure should trigger the following KNX actions simultaneously. Each action is a separate KNX group address sent by the binary input module in ETS6 using linked group addresses.

Cable requirements for fire relay wiring

Wiring between the fire alarm panel and the KNX binary input module has two distinct segments with different cable requirements. Getting this wrong is the most common installation error on fire-integrated KNX projects.

Galvanic isolation: mandatory between fire panel and KNX

The fire alarm panel's relay output must never be connected directly to a KNX binary input without galvanic isolation. The fire panel operates on its own certified 24V DC supply; the KNX bus operates at 29V DC. Mixing these circuits risks damaging the fire panel, creating earth loops, and — critically — compromising the EN 54-2 certification of the fire system.

KNX safety priority configuration in ETS6

KNX actuators support a priority mechanism that prevents lower-priority commands from overriding safety-critical states. For fire integration, the fire alarm telegram must use the highest available priority so that no scene, timer, room thermostat or HVAC setback command can cancel the fire-state actions.

Cause-and-effect matrix

The cause-and-effect matrix documents every event source, its KNX group address, the action triggered, the priority level and the reset condition. This document must be produced during design, reviewed by the fire engineer and retained with the building's fire O&M manual.

BS 5839-1 (UK) vs EN 54-2 (EU) comparison

Both standards govern the design, installation and commissioning of fire detection and alarm systems, but differ in scope, detection classification and certification requirements. On projects spanning multiple countries, confirm which standard applies in each jurisdiction — they are not interchangeable.

Priority logic: fire telegram override rules

The KNX priority mechanism ensures the fire alarm state cannot be accidentally cancelled by normal building automation functions. Understanding the override hierarchy is essential for correct ETS6 configuration.

Priority 3 — Safety (fire alarm):
  DPT 1.001 value 1 — set by fire alarm relay input
  Cannot be overridden by any lower-priority telegram
  Actuator holds fire state until Priority 3 reset received

Priority 2 — Urgent:
  HVAC emergency stop (CO2 alarm, smoke ventilation)
  Can override Priority 1 and 0 commands
  Cannot override Priority 3 (fire alarm)

Priority 1 — Normal:
  Standard KNX control: scenes, switches, dimmers
  Room thermostat setpoints, occupancy-based scenes
  Overridden by Priority 2 and 3

Priority 0 — Low / scene:
  Timer events, scheduled scenes, astronomical clock
  Lowest precedence — overridden by all other priorities

Reset rule:
  Fire state (Priority 3) clears only when:
  (1) Fire panel is reset and alarm output relay opens
  (2) KNX binary input sends DPT 1.001 value 0 on group address
  (3) Actuator receives Priority 3 reset telegram on the same GA
  Manual override of fire state by building user is NOT possible