EN 1155 · EN 54-4 · KNX relay · Fail-safe · 8 min read

Fire Door Holders and Electromagnetic Door Release: EN 1155 and KNX Control

Electromagnetic door holders keep fire doors open for daily building use and release automatically on fire alarm, closing the door to contain fire and smoke. This guide covers EN 1155 compliance, fail-safe 24V DC wiring, the correct release hierarchy between fire panel and KNX, acoustic door holders for retrofit, and the installation mistakes that cause fire safety inspection failures.

Safety notice:Fire door holder systems are life-safety components. Installation and commissioning must be carried out by engineers competent in BS 5839-1 (UK) or EN 54 (EU). The fire panel must be the primary release trigger — KNX may only be used as a secondary or supplementary release. Any modification to a fire door installation must be reviewed by a fire engineer and recorded in the building's fire O&M documentation.

Fire door purpose and EN 1155 fail-safe principle

Fire doors serve a single critical function: compartmentation. When closed and latched, a fire door prevents fire and smoke from passing between building zones, protecting escape routes and limiting fire spread for the duration defined by the door's fire resistance rating (FD30, FD60, FD90).

For operational convenience — high-traffic corridors, accessible facilities, care homes — fire doors can be held open by electromagnetic door holders. EN 1155 defines the fail-safe principle that all door holders must follow:

EN 1155 fail-safe principle

Normal building operation:
  24V DC power supplied to door holder electromagnet
  Electromagnet energised → door held open against magnet face plate
  Door remains open for normal building use

Fire alarm (or power failure):
  24V DC supply interrupted → electromagnet de-energises
  Door spring/closer releases → door swings closed and latches
  Fire compartmentation restored — door remains closed until manually re-opened

Power failure (mains failure or panel fault):
  EN 54-4 certified battery-backed power supply maintains 24V DC for ≥72 hours
  Holder remains energised during short power interruptions
  If battery is flat or supply fails → door closes automatically (safe state)

Critical rule:
  Power ON = door held OPEN
  Power OFF = door CLOSED (safe position)
  Never wire a door holder in a way that requires power to keep the door CLOSED

EN 1155 certified door holder products

Use only EN 1155 certified door holders. Certification confirms the holding force, release time, environmental operating range and electrical safety of the device. Common certified products used on KNX-integrated commercial projects:

Dorma Magtis 500N

• EN 1155 certified — 500N holding force
• Wall-mounted electromagnet with floor plate
• 24V DC, 0.4A — standard wired installation
• Release time under fire alarm: < 1 second
• Available in 200N, 350N and 500N versions — match to door size
• Concealed or surface-mounted wiring options

Geze TS5000E

• EN 1155 certified — combined door closer and electromagnet
• Overhead closer with built-in hold-open arm
• 24V DC electromagnetic retention in the arm linkage
• Power-off releases the arm — door closes via overhead spring
• Suitable for heavy doors up to 1400mm leaf width
• Single device: closer + holder — reduces installation time

Samuel Heath Powermatic

• EN 1155 certified concealed door closer
• Electromagnetic hold-open built into floor pivot
• Ideal for glass doors and architectural installations — concealed mechanism
• 24V DC supply via floor conduit — no visible cable on door
• Available for doors up to 120kg leaf weight
• Release via fire panel output or manual release button

Agrippa acoustic fire door retainer

• No power cable required — internal lithium battery
• Microphone detects BS 5839 fire alarm tone: 3.75kHz or 520Hz warble
• On detection: solenoid releases door immediately
• BAFE SP203 certified — tested to BS 7273-4
• Ideal for retrofit where running 24V cable to door frame is impractical
• Battery life: 1 year typical — low battery LED warning

24V DC power supply wiring requirements

The 24V DC power supply for door holders must meet EN 54-4 (Power Supply Equipment for Fire Detection and Fire Alarm Systems). This is not the same as a general-purpose 24V power supply, a KNX bus power supply, or a standard panel 24V rail.

EN 54-4 certified supply requirements

• Mains-powered with sealed lead-acid or lithium backup battery
• Battery capacity: minimum 72 hours standby (EN 54-4 Clause 6)
• Fault monitoring: panel detects mains fail, battery low, battery fail
• Output voltage: 24V DC, regulated — typically ±15% tolerance
• Example: Elmdene EN54-4 range, Vimpex EN54-4 series, Rako EN54-4 PSU
• Must be installed in a locked panel or cabinet — not accessible to building users

What NOT to use as supply

KNX bus 29V: Not EN 54-4 certified, not isolated for fire safety circuit use
Standard panel 24V rail: Not battery backed to EN 54-4 standard — power failure closes all doors without alarm
Generic SMPS 24V: No battery backup, no fault monitoring — fails EN 54-4 requirement
Access control 12V/24V supply: Different circuit, different certification — do not share with fire door holders

Door holder wiring architecture

EN 54-4 certified 24V DC supply (battery backed, fault monitored)
    │
    │ Fire-rated cable: EN 50200 FE180/E90 or FPLR 2×1.5mm²
    │ Separate conduit from all other building cables
    │
    ▼
Contactor / relay (switched by fire panel alarm relay output)
    │
    │ Normally CLOSED path → 24V DC flows → door holders energised (OPEN)
    │
    │ On fire alarm: relay coil energises → contact opens → 24V cut → doors CLOSE
    │
    ▼
Fire door holders (zone 1)    Fire door holders (zone 2)    etc.
  24V DC → energised            24V DC → energised
  Door held OPEN                Door held OPEN

Note: KNX relay may switch a SECONDARY contactor in series,
but must NEVER replace the fire panel relay as the primary release path

Release method hierarchy

Three release methods can be used in a door holder system. They must be configured in a strict hierarchy — the fire panel is always primary and cannot be bypassed by KNX or any other secondary control.

Primary release: fire panel alarm relay (mandatory)

The fire alarm panel's volt-free alarm relay output directly switches a contactor that cuts the 24V DC supply to all door holders in the affected zone. This is the mandatory primary release path — it must operate independently of all other systems. If the KNX system fails, the fire panel release must still function correctly.

Secondary release: KNX relay output (supplementary only)

A dedicated KNX safety relay actuator (not a standard KNX dimmer or switching actuator) can provide a secondary release path — reading the fire panel alarm relay via a KNX binary input module and switching a second contactor in series. This is supplementary only: the fire panel relay remains the primary release. KNX must not be configured as the only release path for any fire door holder.

Building management release: daily time-switch (non-fire use only)

For corridor traffic management, KNX time-switch logic can hold fire doors open during office hours (e.g. 09:00–17:00) and close them after hours. This uses the same KNX relay controlling the door holder supply but is not a fire release — it is a building management function. After-hours closure reduces hinge wear and prevents corridor draughts. This mode must be clearly documented as non-fire-related in the O&M manual, and must not affect the primary fire panel release path.

KNX integration for daily door management

Beyond fire release, KNX can automate the daily hold-open and release cycle for fire door holders — reducing unnecessary closed-door periods and integrating with building occupancy schedules.

ETS6 time-switch configuration

KNX binary output (relay actuator) wired to 24V contactor controlling door holders
ETS6 timer: Mon–Fri 09:00 → output ON → contactor closes → 24V to holders → doors OPEN
ETS6 timer: Mon–Fri 17:00 → output OFF → contactor opens → doors CLOSE (after-hours)
Weekend: doors remain closed (no time-switch action)
Fire alarm group address: priority-3 telegram → output forced OFF → doors CLOSE immediately
Fire reset: priority-3 cleared → time-switch resumes → doors re-open if within office hours

KNX binary input: fire panel monitoring

MDT STC-0416.02: Reads fire panel alarm relay via volt-free input. On contact close: sends DPT 1.001 value 1 on group address 1/1/5 (door holders release).
Inverter logic: If using an NC relay output from the panel, configure the binary input for inverted logic — contact open = event active.
Priority: Group address 1/1/5 configured at priority 3 on the KNX relay actuator — overrides time-switch and any manual KNX command.
Reset: Fire panel clears → relay contact opens → binary input sends value 0 → time-switch logic resumes.

Acoustic door holders: retrofit solution

Where running a 24V fire-rated cable to a door frame is impractical — in listed buildings, existing structures, or locations where chasing is not permitted — acoustic door holders provide a cable-free solution.

Agrippa acoustic door retainer — how it works

• Internal lithium battery — no power cable to door frame required
• Built-in microphone listens continuously for fire alarm tone
• Detects standard BS 5839-compliant tones: 3.75kHz continuous or 520Hz warble
• On tone detection: internal solenoid retracts → door closes via door closer
• BAFE SP203 certified, tested to BS 7273-4:2015
• Holding force: 60N (suitable for standard FD30 corridor doors)

• Battery life: approximately 12 months — low battery LED indicator
• Manual release: press button on unit — door closes immediately
• Reset: re-open door and press button — holder re-engages
• Limitation: requires audible alarm to be active in same space — not suitable for areas where fire alarm sounders are silenced or remote
• Not suitable as only release method where BS 5839-1 requires hard-wired release
• Ideal for: listed buildings, retrofits, corridors without conduit access

Door closer compliance

A door holder is only effective if the door closer reliably closes and latches the fire door on release. Door closer selection and sizing must be confirmed against the door specification — an undersized or incorrectly adjusted closer is a common reason for fire door failures during inspection.

EN 1634-1 tested doors

• Fire door must carry EN 1634-1 test evidence
• FD30 (30 min), FD60 (60 min), FD90 (90 min) — match to compartmentation requirement
• Door leaf, frame, ironmongery and closer must all be on the same test evidence
• Modifying a fire door (cutting cable holes, changing hinges) may invalidate test evidence

Overhead closers (EN 1154)

• Sized to door weight and opening angle
• EN 1154 grade: grade 3 for doors up to 950mm, grade 4 for up to 1100mm, grade 5 for up to 1400mm
• Closing force must latch the door positively — check against door seal compression
• Adjust backcheck to prevent door slamming — but closing speed must not be reduced below latch clearance

Floor springs (heavy doors)

• For heavy doors over 100kg or leaves wider than 1200mm
• EN 1154 certified floor spring with adjustable closing speed
• Concealed in floor — suitable for architectural installations
• Requires access floor plate for adjustment — design into floor finish
• Check floor finish depth is sufficient before specifying

Common installation mistakes

The following mistakes are found on a significant proportion of fire door holder installations during inspection. All of them cause either immediate inspection failure or create a latent life-safety risk.

Mistake	Why it fails	Correct approach
Using a standard 24V SMPS supply (not EN 54-4 certified)	No battery backup — mains power failure closes all doors without fire alarm. Fails EN 54-4 requirement. Inspection failure.	Specify EN 54-4 certified supply with ≥72h battery backup and fault monitoring output to fire panel
Running door holder cable in same conduit as power cables	Thermal damage to fire-rated cable in the same conduit reduces circuit integrity — may fail at the moment fire reliability is most critical	Separate conduit for fire safety circuits. Minimum 50mm separation from power cables. Fire-resistant fixings throughout.
Using KNX relay as the primary (only) release path	KNX relay actuators are not EN 54 certified fire safety devices. If KNX logic fails, hangs or loses power, fire doors cannot release. Not compliant with BS 5839-1 or EN 54.	Fire panel alarm relay is always primary. KNX relay is secondary supplementary release only, wired in series with (not replacing) the fire panel contactor.
Connecting door holder 24V supply to KNX bus (29V)	KNX bus is 29V — above rated supply voltage for 24V door holders. Also not battery-backed for fire use or EN 54-4 certified.	Separate, dedicated EN 54-4 24V DC supply for all door holder circuits. Never shared with KNX bus.
Failing to test battery backup on EN 54-4 supply	Battery may be flat, disconnected or past service life. Mains failure during fire alarm would close all doors immediately — defeating the system purpose.	Annual test: disconnect mains supply, verify door holders remain energised for the required standby period. Record test result.
Door closer not latching door reliably after holder releases	A fire door that swings closed but does not latch provides no fire compartmentation — smoke and fire gases pass through the unlatched gap.	Test every door by releasing holder manually — verify door swings closed, reaches latch position and latches under door closer force alone. Adjust closing speed if needed.

Testing regime

Door holder systems must be tested on a documented schedule. All tests and results must be recorded in the building's fire logbook — required by BS 5839-1 and the Regulatory Reform (Fire Safety) Order 2005 (UK) / relevant EU fire safety regulation.

Weekly visual check

• Visually confirm each fire door is in its correct held-open position
• Check no obstructions prevent door closing
• Confirm indicator LEDs on door holders are illuminated (where fitted)
• Log any door that is propped open by wedge or other means — immediate corrective action

Monthly release test

• Isolate 24V supply to door holder circuit (or use test button on panel)
• Verify every door in the zone swings closed and latches positively
• Inspect latch engagement — door must not bounce back open
• Restore 24V supply — verify all holders re-engage
• Log test results including any failures

Annual full BS 5839-1 / EN 54 test

• Full fire alarm system test under fire panel activation
• Verify fire panel alarm relay activates contactor correctly
• Verify KNX secondary release operates (if fitted)
• Verify all door holders release on fire alarm activation
• Verify EN 54-4 battery backup: disconnect mains — confirm doors hold open
• Issue annual fire system service certificate

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