Fire alarm systems must integrate with building automation for life safety functions: overriding lighting to full brightness, recalling lifts to ground floor, shutting down HVAC fans to prevent smoke spread, releasing magnetic door holders, and activating smoke ventilation dampers. KNX is the building automation layer that receives fire panel output signals and coordinates these responses. Getting the integration right — correct cable, correct galvanic isolation, correct priority logic — is a critical engineering responsibility.

IMPORTANT: Fire alarm systems must be designed, installed and commissioned only by qualified engineers certified to EN 54-2 (EU) or BS 5839-1 (UK). The KNX integration described here extends fire panel outputs — it does not replace or substitute for a dedicated EN 54-certified fire detection system.

Fire panel output types

Addressable fire alarm panels (Bosch FPD-7024, Notifier ID3000, Advanced MxPro5, Hochiki DCP) provide volt-free dry-contact relay outputs for alarm, fault and zone events. These contacts are certified outputs defined in EN 54-2: Clause 7.8 (fire alarm output), Clause 7.11 (fault output), Clause 7.12 (alarm zone output). The contacts are rated typically 24V DC, 1A (resistive load). Normally open (NO) or normally closed (NC) configuration — use NO contacts for KNX integration (contact closes on alarm).

Galvanic isolation: mandatory

Fire panel dry contacts must never connect directly to the KNX bus. The KNX bus operates at 29V DC; fire panels have their own power supply and ground reference. Connecting them without galvanic isolation creates a ground loop that can damage both systems and introduce noise onto the KNX bus. Use an optocoupler interface between the fire panel contact output and the KNX binary input module: fire panel dry contact → 24V DC supply (from fire panel AUX 24V output, EN 54-4 certified) → optocoupler LED → optocoupler transistor output → KNX binary input module (MDT STC-0416.02). The 24V supply for the optocoupler must be from the fire panel's EN 54-4 certified battery-backed supply — not from the KNX panel 24V.

Cable specification for fire relay wiring

Wiring from fire panel relay output to KNX binary input must use fire-rated cable. EN 50200 PH30/E30 cable (30 minutes integrity) minimum for building without sprinkler protection. EN 50200 PH90/E90 cable (90 minutes integrity) for escape routes and stairwells. The fire-rated cable runs from the fire panel output to the optocoupler input. After the optocoupler (KNX side), standard LSZH cable is acceptable. Never run fire-related cable in the same conduit as standard power cables or KNX bus cable — separate fire circuit cable run, typically red-marked trunking or conduit.

KNX binary input configuration

MDT STC-0416.02 4-channel binary input (or similar): configure the channel connected to fire alarm relay as "Switch (1-bit), value on rising edge = 1, value on falling edge = 0". Cyclic sending: enable every 60 seconds with current state — provides heartbeat monitoring in the KNX logic. Debounce time: set to 100-200ms (fire relay contacts may bounce once on contact closure). The binary input sends DPT 1.001 value 1 to group address 9/0/0 (fire alarm general) on fire relay closure.

KNX safety priority: essential configuration

All KNX actuators that participate in fire emergency response must have KNX safety priority configured in ETS6. Safety priority means the fire alarm telegram (sent with high priority bus access) cannot be overridden by normal priority scene, thermostat or manual commands. In ETS6 parameter page for MDT switch actuator: enable "Bus voltage failure behaviour" = defined state. Enable "Priority function" = enable. Priority group address: bind to fire alarm GA 9/0/0. Priority value when active: lights → ON (100%), HVAC fans → OFF, door holders → OFF (release). Priority recovery: when fire alarm GA returns to 0, actuator returns to normal operation.

The priority function in KNX actuators means: even if a KNX thermostat sends "HVAC fan ON" command (normal priority), the fire priority input holding the fan OFF takes precedence. The fan remains off until the fire alarm is cleared (GA 9/0/0 returns to 0), regardless of any other KNX commands received during the alarm.

Cause-and-effect matrix for commercial buildings

| Fire event | KNX group address | DPT | KNX action | Priority | |---|---|---|---|---| | General fire alarm | 9/0/0 | 1.001 | All lights ON 100% | High | | General fire alarm | 9/0/0 | 1.001 | HVAC supply fans OFF | High | | General fire alarm | 9/0/0 | 1.001 | Smoke dampers CLOSE | High | | General fire alarm | 9/0/0 | 1.001 | Lifts → ground floor | High | | General fire alarm | 9/0/0 | 1.001 | Door holders release | High | | General fire alarm | 9/0/0 | 1.001 | Access control all UNLOCK | High | | Zone 1 alarm | 9/0/1 | 1.001 | Zone 1 smoke ventilation OPEN | High | | Fault output | 9/0/10 | 1.001 | Visualisation fault alert | Normal |

Configure each row as a separate KNX binary input channel (or KNX logic gate receiving the same fire GA and switching multiple actuator GAs). Each actuator receiving a fire command must have the safety priority function enabled.

Reset procedure

Fire alarm reset requires deliberate engineering. The fire panel reset extinguishes the relay outputs — this sends fire GA 9/0/0 = 0 to KNX. Actuators with safety priority automatically return to normal operation. Lights must return to pre-alarm state (not all-OFF which would leave a dark building). Configure actuator "priority off" behaviour: return to last state before priority activation, or return to a fixed state (e.g. 50% lighting). HVAC fans: return to normal HVAC schedule (not immediate full-speed restart — a delayed start prevents pressure spikes). Smoke dampers: return to automatic position control. Document the reset sequence in the O&M manual for the building operator.

Testing fire KNX integration

Test procedure (coordinate with fire alarm commissioning engineer): (1) Isolate the fire zone under test to prevent actual evacuation alarm (put panel into test mode), (2) activate fire zone from detector or break-glass unit, (3) verify dry contact output closes on fire panel, (4) verify optocoupler output drives KNX binary input, (5) verify KNX group address 9/0/0 = 1 visible in ETS6 Group Monitor, (6) verify all actuator responses: lights, HVAC fans, door holders, (7) reset fire panel, verify KNX returns to normal state. Complete test certificate with all results, signed by both the fire alarm commissioning engineer and the KNX commissioning engineer. Retain with panel documentation.