What EN 81-20 requires from a door protection device
The requirements specific to door detectors sit in EN 81-20 clause 5.3.6.2.1.1, "Protection in relation to door operation". This is the version that matters when you buy, audit or replace a device.
| Requirement | EN 81-20 value / limit |
|---|---|
| Detection zone above the car door sill | 25 mm to 1,600 mm |
| Minimum detectable obstacle | 50 mm diameter, tested on site with a calibrated cylinder |
| Maximum kinetic energy at average closing speed | 10 J |
| Device may be inactive in the last | 20 mm of door closing travel |
| Average closing speed measured excluding | 25 mm at each end of travel for centre-opening doors, 50 mm for side-opening |
| Required behaviour if the device fails or is switched off | Closing energy limited to 4 J with an audible warning, or reduced closing speed with a warning, or the lift is stopped |
| Top of the detection zone before EN 81-20 | 1,800 mm under EN 81-1, reduced to 1,600 mm under EN 81-20 |
Two consequences are routinely missed. First, "50 mm across 25–1,600 mm" is a detection performance, not a beam count - a curtain with wide beam spacing can span the full height and still let a 50 mm object through between two beams. Second, the 4 J escape route is not an alternative to a working detector; it is the fallback that keeps a lift in service at reduced risk while the repair is scheduled.
The three generations of door protection, and where each stands today
Single-beam infrared photocells ("electric eyes"). One or two beams shot across the entrance at a fixed height. Cheap, contactless, and blind everywhere else - a curious child or a dog below the beam is simply not seen. KONE's own EN 81-20 factsheet states the position plainly: lifts are required to incorporate a curtain-of-light mechanism, and "photocell-based mechanisms will not be compliant" with the current standard. If you still find one of these on a lift, it belongs on the modernization list, not on the spares list.
Retractable mechanical safety edges. A rubber-coated contact strip mounted on the leading edge of the car door. When the strip meets a person or an object, it is pushed back against the direction of travel, internal switch contacts open, and the door controller reverses. Its virtue is that it has no blind spot at all. Its weaknesses are that it protects only after contact, and that every part of it is a wear item: rubber strip, spring, pivot, micro-switch and spiral cable. It cannot satisfy 5.3.6.2.1.1 on a power-operated sliding car door, because the standard requires automatic reopening when a person crosses the entrance during the closing movement - before contact, not after it.
Light curtains. An array of infrared emitters in one housing and detectors in the other, with each emitter/detector pair checked in sequence. A single interrupted beam is enough to send a reopening signal to the door controller. Production arrays now run from roughly 32 beams to more than 160, covering the required 25–1,600 mm zone, and detection capability down to 14 mm on the densest models. These are contactless, almost wear-free, and self-diagnosing - which is why they replaced the mechanical edge on new equipment and on most modernizations.
3D entrance monitoring. Adds a time-of-flight depth sensor (usually transom-mounted) to the 2D beam plane, so the device detects a person approaching the door rather than only someone standing in the opening. The 2019 edition of ASME A17.1 / CSA B44 defined detection of persons between the doors (2D) and in the entrance area (3D); A17.1-2022 and A17.1-2025 build on those rules. In Europe, 3D is a comfort and nuisance-trip fix rather than an EN 81-20 obligation - but on a busy hospital or hotel landing it is the difference between a lift that runs and a lift that keeps re-opening.
Parallel or criss-cross beams: the detail that decides real-world performance
Parallel beam curtains aim every beam straight across the opening. Criss-cross curtains angle beams up and down from alternating positions in the housing. The practical difference appears in the last 20 mm of travel, exactly where the standard allows the device to be inactive: criss-cross geometry keeps beams crossing the gap almost to full closure, while a parallel array leaves a widening unchecked band as the panels approach each other.
Beam spacing sets the true detection capability. The table below shows the configuration bands used in the industry; the point is to buy the performance you need for the traffic, not the cheapest array that covers the height.
| Configuration | Beam spacing | Detectable object | Typical beam count | Where it fits |
|---|---|---|---|---|
| Parallel, wide spacing | 30 mm and up | Approximately 40 mm+ | 24–48 | Budget retrofits; verify it still detects 50 mm |
| Parallel, standard | 20 mm | Approximately 25 mm | Around 80 | Residential and low-traffic commercial lifts |
| High-density parallel | 10 mm | Approximately 14 mm | 150+ | Hospitals, public buildings, freight with trolleys |
| Criss-cross | 10 mm angled | Approximately 14 mm | Model dependent | Full EN 81-20 compliance, detection active to door closure |
Head to head: mechanical safety edge vs light curtain
| Criterion | Mechanical safety edge | Light curtain (2D) | Light curtain with 3D sensor |
|---|---|---|---|
| Detection principle | Physical contact deflects a contact strip | Contactless infrared beam array | Infrared beam plane plus time-of-flight depth |
| Contact with the passenger | Required before the door reverses | None | None |
| Compliance with EN 81-20 5.3.6.2.1.1 | Not compliant on power sliding car doors | Compliant when the 25–1,600 mm / 50 mm performance is met | Compliant, with better nuisance-trip behaviour |
| Blind spots | None across the covered edge | Possible between beams and beyond the array height | Smallest - depth coverage also detects approach |
| Wear parts | Strip, spring, pivot, micro-switch, spiral cable | None mechanical; cable and connector only | Same as 2D plus the sensor unit |
| Maintenance burden | High - adjustment and replacement are routine | Low - cleaning plus periodic functional test | Low, plus firmware and diagnostics review |
| Environmental sensitivity | Mechanical, unaffected by light | Sunlight and reflective floors can cause false trips | Depth filtering rejects most cross-traffic |
| Typical failure mode | Stops reversing or reverses constantly | Nuisance reversals, then no detection as beams age | Trip from a masked or dirty sensor |
| Best suited to | Older hinged or manual doors, legacy goods lifts | New installations and standard modernizations | High-traffic, hospital, hotel, glass-walled cars |
Specifying the device: eight points to fix before you order
Detection zone. 25 mm to 1,600 mm is the minimum. Choose the active protection height to match the opening - 1,582 mm, 1,822 mm and 1,900 mm are the common catalogue heights, and freight doors over 2,400 mm need more.
Resolution. 50 mm maximum gap for EN 81-20; specify 10–20 mm spacing for lifts used by children, pets or trolleys, and for accessible lifts where EN 81-70 applies.
Output type. Match the door controller input: PNP, NPN or push-pull. Legacy AC controllers typically need an interface power supply with a relay output.
Supply. 24 V DC is standard, with 18–30 V working ranges on most models; universal kits that accept 220 V AC exist for retrofits.
Environmental rating. IP65 as a working minimum, IP67 for parking garages, car washes and dusty shafts. For glass-walled cars, insist on high light immunity - ratings above 100,000 lux are the benchmark.
Response time. Between roughly 6 ms and 100 ms depending on the model. A slow curtain on a fast door closes late; check the number against the closing speed.
Mounting. Edge-mounted on the moving car door or transom-mounted for 3D. Confirm hole centres and housing profile against the unit you are replacing so the retrofit takes minutes, not a shift.
Door geometry. Opening width, centre-opening or side-opening (two curtains or a folding arrangement), and door height. A centre-opening door needs both panels clear, not just one.
Mounting and commissioning
The lowest beam must sit no more than 25 mm above the car door sill - mount it higher and the last 25 mm of the sill gap is unprotected. Align the transmitter and receiver so the lenses face each other squarely along the full travel, then check the LED status on both units. On a new installation, run the door slowly through its cycle and confirm the array reports normal at both ends of travel.
Commissioning is a functional test, not a visual one. Take a 50 mm calibrated cylinder and pass it through the opening at low, mid and high level, at the centre and near both edges. The door must stop and reopen every time. Repeat during the closing movement to confirm the required reversal, and verify the failure mode: with the sensor deliberately disabled or reporting a fault, the controller must limit closing energy to 4 J with an audible warning during closing, or reduce speed with a warning, or stop the lift. Record the test - that record is what a maintenance audit or a notified body asks to see.
Maintenance that keeps door sensors off the call-out list
| Interval | Task | Reason |
|---|---|---|
| Monthly | Visual check of both lenses and the LED status indicators (green normal, red fault); clean with a lint-free cloth and isopropyl alcohol if dusty | Scratched or soiled lenses scatter infrared light and degrade detection |
| Quarterly | Functional test with the 50 mm test cylinder at three heights; inspect cables, connectors and the spiral cable at the moving panel | Confirms the device still meets the required performance, not just that it powers up |
| Annually | Full alignment verification, connector check, error-log review on self-diagnosing units | Catches slow drift and cabling fatigue before they become breakdowns |
| On every modernization | Re-verify the device against 25–1,600 mm and 50 mm detection, and re-check the door kinetic energy | A device can pass while the door it protects has become faster or heavier |
Troubleshooting: symptom, cause, action
| Symptom | Likely cause | Action |
|---|---|---|
| Doors reverse on arrival with nobody there | Cross-traffic on a busy landing, reflected sunlight, dirty lenses, drifting alignment | Clean and re-align, fit a hood or shade, consider a 3D sensor or criss-cross array |
| Door closes on a person or trolley low down | Array mounted high, or a wide-spacing curtain with a blind spot near the sill | Lower the bottom beam to 25 mm above the sill, or replace the curtain with a denser array |
| Reversal is always late | Response time too slow for the closing speed, or a controller input filter | Measure response time, check controller settings, replace the sensor if it does not meet specification |
| Reversal happens at one landing only | Landing door vane, clutch or sill obstruction - not the sensor | Inspect the landing door and sill before ordering parts |
| Fault indication on the curtain, intermittent | Broken conductor in the moving-panel cable, water ingress, low supply voltage | Replace the spiral or flex cable, reseal the housing, check the 24 V supply under load |
| Mechanical edge no longer reverses the door | Hardened or split rubber strip, short switch actuation travel, broken spiral cable | Adjust or replace the edge; treat repeated failures as a signal to convert to a light curtain |
| Doors will not close at all | Sensor output stuck active, permanent detection, wiring fault | Measure the output at the controller terminals; isolate sensor from controller |
Converting a mechanical edge to a light curtain
The conversion is one of the easiest modernization jobs on a lift, and it removes a whole category of call-outs. Follow this order:
Record the door: opening width and height, centre-opening or side-opening, door controller brand and model.
Photograph the existing edge and its mounting hole pattern.
Confirm the controller input type (PNP, NPN or relay) and the available supply voltage.
Select a curtain with the right protection height and 24 V DC operation, ideally with universal mounting brackets.
Remove the old contact strip and cable; retain the existing wiring route where possible.
Mount the transmitter and receiver housings, with the lowest beam no more than 25 mm above the sill.
Wire the outputs. On legacy AC controllers, use an interface power supply with a relay output.
Test with the 50 mm cylinder at three heights and both closing and opening movements, verify the failure mode, and record the result on the maintenance file.
Sensor part numbers we stock and cross-reference
RelyElevator carries the optoelectronic switches that OEMs fit in the car door and door-zone circuits, and we cross-reference light curtains and 3D entrance sensors against photographs, nameplates and OEM sales codes. Current examples from stock:
Hitachi photoelectric switch GLS126 - view part
Hitachi photoelectric switch GLS326 - view part
Mitsubishi photoelectric switch YA043D166-04 - view part
Toshiba photoelectric switch G92007050973 (OK-TNJ-F14) - view part
Hyundai scan sensor BA2M-DDT, auto-stop / auto-start entrance detection - view part
Leveling and position sensors used by the same door and door-zone circuits are listed under the Hitachi sensors, Otis sensor, Kone leveling sensors, Mitsubishi sensors, Toshiba sensors and Hyundai sensors categories. The mechanical half of the door - hangers, sliders, locks and motors - is covered in our door operator guide, and the lock side of door safety in the door lock guide.
For light curtains and 3D sensors as complete assemblies (the CEDES cegard and easygard families, and Formula Systems Vision Plus and Safescreen families), order against performance class, protection height, output type and mounting pattern: those four values decide compatibility, and we quote the matching interface power supply with the curtain. Where a modernization has to be justified against the EN 81-20 standard, the difference between an OEM and an equivalent unit is set out in our OEM vs aftermarket guide.
