Wiring diagram
Correct wiring
Motion sensor instead of a switch
For a hallway, an entrance hall or a storeroom — places where light is needed briefly and your hands are often full. A 3-wire wall sensor takes the place of the switch by the door, in a deep back box, but unlike a switch it needs a neutral: terminals L, N and ↓. From the consumer unit to the sensor, a 3×1.5: brown straight to L, blue and green-and-yellow to lever connectors, and a short link from the neutral connector to the sensor’s N. To the light, another 3×1.5: brown from output ↓, blue and green-and-yellow from the same lever connectors.
What happens
Light: off
Live
Cables
| From → to | Cores × size |
|---|---|
| Panel → Door | 3×1.5 mm²green-and-yellow, blue, brown |
| Door → Light | 3×1.5 mm²green-and-yellow, blue, brown |
What to buy
- B10 MCB for the lighting circuitin the consumer unit, if there is no separate lighting circuit yet1 pcs
- 3-wire motion sensor (L, N, ↓)1 pcs
- Frame, 1-gang1 pcs
- Deep back box, 60 mm1 pcs
- Lever connector for 2 wires1 pcs
- Lever connector for 3 wires1 pcs
- 3×1.5 mm² cable — one run2 pcs
How a motion sensor and a twilight switch work
A motion sensor is a switch with its own electronics. The live arrives at terminal L and leaves for the lamp from output ↓, and the electronics need power between L and N, so unlike an ordinary switch, the sensor needs a neutral. When it detects movement, the sensor connects L to ↓, and after the last movement it keeps the light on for a while — set with a knob on the housing. A sensor also has its own light threshold: while it is light, it does not switch the light on. The interactive diagram has no timer or threshold: the “Motion detected” input simply closes the contact.
A twilight switch turns the light on when it gets dark. The DIN-rail module sits in the consumer unit and is powered from L and N, while the light level is measured by a remote light sensor outside. Its output contact is volt-free: there is no live of its own on it, so the live is fed to the common terminal with a short link from the MCB and goes from the other terminal of the contact to the lamp. Many twilight switches have a switch-on and switch-off delay, so the headlights of a passing car do not make the light blink.
Terminal markings vary between makers. On a Steinel sensor the terminals are L, N and L — the output carries the same letter; in the diagram above it is marked with an arrow ↓. On a Finder twilight switch the supply is A1 and A2 and the contact 11 (common) and 14; on Theben it is L and N, with contact 1-2-3. In the diagram above the supply is marked L and N and the contact 1 and 2; for your own device, check the diagram on it.
Motion sensor: what to buy and how to switch the light on manually
For ordinary wiring, choose a 3-wire sensor: L, N and ↓. In place of a switch, fit a wall sensor for a back box; many makers offer one in the same ranges as their switches, to fit the same frames. It needs a deep 60 mm back box: besides the sensor, it holds the neutral and earth lever connectors. There are also 2-wire sensors without a neutral — a different device that draws its power through the lamp, like a no-neutral smart switch. It needs a minimum load, from 2 W for the Legrand 0 952 11, and if the light misbehaves, a compensator is fitted at the light fitting. With several such sensors on one circuit, the minimum load goes up. For a porch or garden, choose a sensor for outdoor use, rated IP44 or higher.
The sensor switches the light off by itself, and sometimes that gets in the way: you are cleaning the storeroom and the light goes off. So plan manual switching in advance, before the cables disappear into the wall. The simplest option is an ordinary switch in a neighbouring back box, wired to bypass the sensor, between its terminals L and ↓, as in the diagram above. Switch on and the light stays on permanently; switch off and the sensor takes over again, but this switch cannot turn the light off while there is movement. If you also need an “off” mode, Steinel shows a diagram with a two-gang switch.
Some sensors have a dedicated push-button input, for example those from Busch-Jaeger and Niko and the Theben LUXA 103. A push-button is then fitted instead of a switch and connected according to the instructions; with Busch-Jaeger, illuminated push-buttons are not suitable for this input. The Busch-Jaeger flush-mounted sensor can also be set to “off”, “auto” and “on” with a slider on the housing.
Twilight switch: when it is the better choice and where to put the light sensor
Most motion sensors already have their own light threshold, so a single lamp with a sensor does not need a separate twilight switch. A twilight switch in the consumer unit pays off when there are several lamps: the porch lantern, path lights and facade lighting all come on together from one light sensor rather than each on its own. Another reason is a timer, when you want light after dark but not all night: choose a twilight switch with a built-in clock or fit a modular timer next to it in the consumer unit, so that the light goes off by itself during the night. And if you want light only on movement and only after dark, the twilight switch powers a motion sensor, as in the “Dusk and motion” diagram.
The light sensor is mounted outside on a north-facing wall, out of direct sun and where the light from the lamp it controls cannot fall on it; for street lighting Theben recommends the east side. Otherwise the lamp itself will light up the sensor, the twilight switch will decide it is dawn and switch the lamp off, then switch it on again in the dark — and round it goes.
The cable to the light sensor is a separate one: up to 50 m for Finder, up to 100 m for Theben at 1.5 mm² and up to 50 m at 0.75 mm². It is not run alongside power cables. On Finder the polarity of the sensor cores does not matter; on Theben it does, so check the markings.
Cables, core colours and the MCB
Core colours are set by HD 308: live is brown, black or grey, neutral is blue, and green-and-yellow is earth only, never live or neutral. The cable runs as a chain: from the consumer unit to the sensor, a 3×1.5; from the sensor to the light, another 3×1.5. In the sensor back box, the brown from the consumer unit goes straight to L, the blues and green-and-yellows of both cables are joined with lever connectors, and a short link runs from the neutral connector to the sensor’s N. That way neutral and earth pass through the back box to the light, and blue stays neutral everywhere. If your home is wired through junction boxes, the circuit is the same, only the place of the joints changes — but the sensor must get a neutral.
A 4×1.5 runs from the sensor to the “always on” switch: brown is the live from terminal L, black runs from the switch output back to ↓, grey is spare and its ends are insulated. A 4×1.5 has no blue core and all the working cores are live colours, so no re-marking is needed. At the sensor the green-and-yellow goes into the earth lever connector, and at the switch to the PE terminal of the device if it has one; otherwise its end is insulated. Earth is taken to every back box, even if the device has no terminal for it: in Germany the standard requires this. From the consumer unit to the porch lamp or the outdoor sensor, another 3×1.5 with no re-marking: brown is the live from terminal 2 of the twilight switch, blue is neutral, green-and-yellow is earth.
Lighting is wired as a separate circuit at the consumer unit: a B10 MCB on 1.5 mm² cable. In Spain, 10 A for lighting is mandatory. In Germany, B16 is also used on 1.5 mm², but only where the standard’s table rates the cable for 16 A (in conduit in a wall or clipped direct to a wall), and not in a thermally insulated wall.
Wiring diagrams
Motion sensor instead of a switch
For a hallway, an entrance hall or a storeroom — places where light is needed briefly and your hands are often full. A 3-wire wall sensor takes the place of the switch by the door, in a deep back box, but unlike a switch it needs a neutral: terminals L, N and ↓. From the consumer unit to the sensor, a 3×1.5: brown straight to L, blue and green-and-yellow to lever connectors, and a short link from the neutral connector to the sensor’s N. To the light, another 3×1.5: brown from output ↓, blue and green-and-yellow from the same lever connectors.
Sensor with an “always on” switch
When you sometimes need the light on for a long time — cleaning the storeroom, doing a job on the stairs — an ordinary switch is fitted next to the sensor to switch the lamp on, bypassing the sensor. It is connected to the sensor’s terminals L and ↓, in parallel with its contact: Steinel shows an “auto — permanent” switch for this on its diagram. The switch sits in a neighbouring back box on the wall, with a 4×1.5 from the sensor to it: brown is the live from terminal L, black brings it back to ↓, grey is spare, and nothing needs re-marking. Switch on and the light stays on; switch off and the sensor takes over again — but this switch cannot turn the light off while there is movement.
Twilight switch: porch light after dark
A porch lantern, path lights or facade lighting come on by themselves when it gets dark and go off in the morning. The modular twilight switch goes in the consumer unit next to the B10 MCB, and its remote light sensor outside on a north-facing wall. The twilight switch is powered from L and N, and the lamp is switched by its output contact 1–2: it is volt-free, so the live is fed to terminal 1 with a short link from the MCB, and from terminal 2 it leaves on the brown core of a 3×1.5 cable straight from the consumer unit to the porch lamp. Neutral to the lamp comes from the neutral bar of the RCD section that the lighting MCB is in, and earth from the earth bar.
Dusk and motion: night lighting
The light at the entrance comes on only when it is dark and someone approaches: the twilight switch output feeds the live to an outdoor motion sensor, so the sensor is unpowered during the day and works as usual at night. From the consumer unit to the outdoor sensor, a 3×1.5: brown is the live from terminal 2 of the twilight switch to the sensor’s L, while blue and green-and-yellow pass through on lever connectors inside its housing and, together with output ↓, go to the porch lamp, also on a 3×1.5. Most sensors have their own light threshold, and for a single lamp it is usually enough. A twilight switch ahead of the sensor is used when the sensor has no threshold of its own, when it is in a poor spot for measuring light, or when you want one light sensor to control several sensors and lamps at once.
Common mistakes
Sensor without a neutral
A 3-wire sensor was connected like an ordinary switch: live on L, the wire to the lamp on ↓, and terminal N was left empty — no link was fitted from the neutral lever connector to it. The sensor has nothing to run on, its contact never closes, and the light never comes on, however much you walk about.
Why this is wrong
There is no danger, but the sensor does not work. It has electronics inside, and they need power between L and N all the time, even when the light is off. Fit a link from the neutral lever connector in the back box to the sensor’s N terminal. If there is no neutral at the switch position — in old wiring often only the live and the wire to the lamp arrive there — run a 3×1.5 cable with a neutral from the consumer unit, as in the diagram above, or choose a 2-wire sensor that needs no neutral: that is a different device, which needs a minimum load and sometimes a compensator at the light fitting. Do not take a neutral from a nearby socket or another circuit: the current would leave on the live of one circuit and return on the neutral of another, and the RCD may trip.
Switch in series with the sensor
The “always on” switch was fitted not to bypass the sensor but in the break of its output: from the sensor’s ↓ terminal the black went to the switch, from the switch the grey came back to a lever connector in the sensor’s back box, and from that connector the brown went to the light. The light only comes on if the switch is on and there is movement. It cannot be switched on permanently, and with the switch off the sensor is simply disconnected.
Why this is wrong
There is no danger, but the switch does not do what it was fitted for. For the light to stay on without movement, the switch must feed the live to the lamp bypassing the sensor: one of its terminals to the sensor’s L, the other to ↓. A switch in series is only good for disabling the sensor completely. If you need all three modes — auto, permanently on and off — Steinel shows a diagram with a two-gang switch for this.
How to wire a motion sensor and a twilight switch, step by step
Switch off the lighting MCB
At the consumer unit, switch off the MCB for the lighting circuit, or the main switch if you are not sure which one it is. If you are fitting the twilight switch in the consumer unit, switch off the main switch. Tell everyone at home so that nobody switches it back on.
Check there is no voltage
First prove your voltage tester or multimeter on a socket you know is live. Then test every core in the sensor and switch back boxes and at the light, and in the consumer unit the terminals of the lighting MCB: between each other and each one to earth.
Bring in the cables and mark the cores
Two 3×1.5 cables come into the sensor back box: from the consumer unit and to the light, and with an “always on” switch, also a 4×1.5 to the neighbouring back box. Label which cable comes from where. In the cable to the switch, stick to one rule at both ends: brown — L, black — ↓, grey spare.
Join neutral and earth in the back box
Put the blue from the consumer unit and the blue to the light into one lever connector, and run a short link from it to the sensor’s N terminal. Join the green-and-yellows from the consumer unit, to the light and, if there is one, to the switch with another lever connector. Insulate the ends of the spare grey.
Connect the sensor, the switch and the light
Brown from the consumer unit to the sensor’s L, brown to the light to output ↓; on Steinel the output is also marked L, so check the diagram on the device. Connect the “always on” switch with the 4×1.5 cable: brown from the sensor’s L terminal to the switch’s L, black from the switch output to the sensor’s ↓. If two wires will not fit into a sensor terminal, join them in a lever connector with a short link and put the link into the terminal. At the light: L — brown, N — blue, PE — green-and-yellow.
Fit the twilight switch in the consumer unit
Clip the twilight switch onto the DIN rail next to the B10 MCB. Live from the MCB to L (A1 on Finder), neutral to N (A2) from the neutral bar of the RCD section that the lighting MCB is in: a neutral from another section’s bar will trip the RCD. With a short link, feed the live from the same MCB to the common terminal of the contact (1 in the diagram, 11 on Finder), and from the other terminal (2, or 14 on Finder) take the brown core of a 3×1.5 cable to the lamp or to the outdoor sensor; the blue of this cable goes to the same neutral bar, the green-and-yellow to the earth bar. In the outdoor sensor housing, neutral and earth pass through to the lamp on lever connectors, as in a back box. Connect the light sensor with a separate cable according to the instructions.
Check and adjust
Switch the MCB on and walk in front of the sensor: the light must come on and go off after the set time. To test during the day, set the light threshold to maximum and the time short, then set your values back. Turn on the “always on” switch: the light must stay on without movement. Test the twilight switch by covering the light sensor with thick cloth: the lamp must come on, sometimes after a delay given in the instructions.
Safety and who may do the work
Only work with the MCB switched off and after testing every core with a voltage tester or multimeter, having first proved the tester on a socket you know is live. The twilight switch goes in the consumer unit: switch off the main switch first and remember that the terminals on its supply side stay live. Who may carry out this work is set by the law of your country. In England, replacing a switch is not notifiable under Part P, but the work must comply with BS 7671. In Germany, changes to the wiring may only be made by an electrician registered with the network operator; in Spain, by an authorised installer; in Poland, by a person with an SEP qualification. In a number of other countries, work on the wiring is for electricians only, so check the rules where you live.
Frequently asked questions
How do I wire a motion sensor in place of a switch?
A 3-wire sensor needs a neutral, so a 3×1.5 runs to it from the consumer unit: brown is the live to L, blue and green-and-yellow go to lever connectors in the back box, and a short link runs from the neutral connector to the sensor’s N. To the light, another 3×1.5: brown from output ↓, neutral and earth from the lever connectors. Use a deep 60 mm back box. If only the live and the wire to the lamp arrive at the switch, there is no neutral there: you need a new cable or a 2-wire sensor. The lighting circuit is protected by a B10 MCB.
Can a motion sensor be wired without a neutral?
Not an ordinary 3-wire sensor: without a neutral its electronics have nothing to run on, and the light will not come on. There are 2-wire sensors that need no neutral, such as the Legrand 0 952 11. They draw power through the lamp, so they need a minimum load — from 2 W for this model — and, if there are problems, a compensator at the light fitting. Do not take a neutral from a nearby socket: it is a different circuit, and the RCD may keep tripping.
How can I make a light on a motion sensor stay on permanently?
Fit an ordinary switch in a neighbouring back box and wire it to bypass the sensor: one wire to the sensor’s L terminal, the other to output ↓. Switch on and the light stays on; switch off and the sensor takes over again. From the sensor to the switch, a 4×1.5: brown and black as live, grey spare, no re-marking needed. If the sensor has a push-button input, connect a push-button to it according to the instructions. Do not put the switch in series with the sensor output: that way it can only disable the sensor.
Where should the twilight switch sensor go?
Outside on a north-facing wall, in the shade, out of direct sun and where the light from the lamp it controls cannot fall on it. Otherwise the lamp will light up the sensor, the twilight switch will decide it is dawn, and the light will keep going off and on in a loop. The cable to the light sensor is run separately from power cables and can be 50–100 m long, depending on the model.