Wiring diagram
Correct wiring
Relay in the consumer unit, three push-buttons
Choose this if there is free space on the DIN rail in the consumer unit: the modular relay goes next to the lighting MCB, the live from the MCB reaches terminal 1 via a short link, and neutral goes to A2. A 5×1.5 runs from the consumer unit to the back box by the door: black from the push-button ↓ to A1, brown is the live from terminal 1 to the push-button L, grey runs from terminal 2 to the light, blue is neutral, green-and-yellow is earth. Grey, blue and green-and-yellow pass through the back box on lever connectors and leave for the light in a 3×1.5 cable, the grey continuing on the brown. From the push-button by the door, a 3×1.5 daisy chain runs to the sofa and on to the hallway: brown on L, blue on ↓ (it is marked with brown tape), and the green-and-yellows are joined at the sofa with a lever connector so that earth reaches the last push-button.
What happens
Light: off
Live
Cables
| From → to | Cores × size |
|---|---|
| Panel → Door | 5×1.5 mm²green-and-yellow, blue, grey, brown, black |
| Door → Light | 3×1.5 mm²green-and-yellow, blue, brown |
| Door → Sofa | 3×1.5 mm²blue, brown, green-and-yellowblue — mark brown |
| Sofa → Hallway | 3×1.5 mm²brown, blue, green-and-yellowblue — mark brown |
Mark a blue core that carries the live with brown tape: this is mandatory in the UK and standard practice elsewhere
What to buy
- B10 MCB for the lighting circuitin the consumer unit, if there is no separate lighting circuit yet1 pcs
- DIN-rail impulse relay1 pcs
- Retractive push-button3 pcs
- Frame, 1-gang3 pcs
- Back box2 pcs
- Deep back box, 60 mm1 pcs
- Lever connector for 2 wires3 pcs
- Lever connector for 3 wires1 pcs
- 3×1.5 mm² cable — one run3 pcs
- 5×1.5 mm² cable — one run1 pcs
- Brown insulating tape or sleeving1 pcs
How an impulse relay works
An impulse relay has a coil and a contact. The coil is connected to terminals A1 and A2, the contact to terminals 1 and 2. Each pulse on the coil changes the contact over: if it was open it closes, if it was closed it opens, and it stays that way until the next pulse. The pulse comes from a retractive push-button: press it and the live reaches A1, let go and it is gone. Pressing changes the light over; releasing changes nothing.
The live to the light goes through the relay contact: it arrives at terminal 1 from the MCB and leaves from terminal 2 to the lamp. So when the light is off, the lampholder is not live.
The push-buttons are connected in parallel, however many there are: the live arrives at terminal L of each one, and the ↓ output of each goes to one common wire to A1. That is why the cable is easiest to run as a daisy chain from button to button rather than from each one separately to the relay. Markings vary between makers: in the diagram above the coil is A1 and A2, the contact 1 and 2, the push-button L and ↓; for your own model, check the diagram on the device.
What to buy: relay, push-buttons, coil voltage
Relays come as modular units for a DIN rail in the consumer unit and as compact units for fitting in a back box. A modular relay in the consumer unit is easy to find and replace, but you will have to run a 5×1.5 from the consumer unit to the back box by the door. A compact relay goes in the back box by the door together with the push-button, and a 3×1.5 from the consumer unit is enough. Check the coil voltage: the diagrams above need a 230 V AC coil. Relays with 12 or 24 V coils are wired differently, through a separate power supply — do not mix them up when buying.
Retractive push-buttons are made in the same ranges as switches, with the same frames. From the outside a push-button looks just like a switch, so check the name and the diagram on the device. Be careful with illuminated push-buttons: their indicator current flows through the relay coil, and the total is limited, usually to 3–5 mA according to the instructions. That is only a few push-buttons: 8–12 at 0.6 mA each for ABB, 4 at 1 mA for the Finder 27.0x. More are possible with the compensator given in the relay instructions, or by giving the push-button lights their own neutral, as Berker suggests.
You will also need a back box and a frame for each push-button, lever connectors, brown tape for the blue cores and, if there is no separate lighting circuit yet, a B10 MCB. Make the back box by the door a deep 60 mm one: besides the push-button it holds the lever connectors and, with a compact relay, the relay itself.
Wiring through the back box by the door, and core colours
With the relay in the consumer unit, a 5×1.5 runs from the consumer unit to the back box by the door, and all five cores are in use: black from the push-button ↓ to A1, brown is the live from terminal 1 to the push-button L, grey runs from terminal 2 to the light, blue is neutral, green-and-yellow is earth. Grey, blue and green-and-yellow do not go to the push-button: they pass through the back box on lever connectors and leave for the light in a 3×1.5 cable, the grey continuing on the brown core. With a compact relay, an ordinary 3×1.5 runs from the consumer unit to the back box by the door, and another 3×1.5 to the light. Blue stays neutral everywhere in these cables, so it needs no re-marking. If your home is wired through junction boxes, the circuit is the same; only the place of the joints changes.
From the push-button by the door to the next one, and on from button to button, runs a 3×1.5: brown is the live to L, blue runs from ↓ back to the relay. Here the blue is live every time a button is pressed, so mark it at both ends with brown tape: this is mandatory in the UK and standard practice elsewhere. The green-and-yellow in the daisy chain continues the earth to every push-button and is not insulated along the way: by the door it goes into the earth lever connector with the others, in each back box along the chain the two green-and-yellows are joined with a lever connector for 2 wires, and at the last push-button the end goes to the PE terminal of the device if it has one, or is insulated otherwise. Earth is taken to every back box, even if the push-button has no terminal for it: in Germany the standard requires this. Green-and-yellow is used only as earth, never as live or neutral.
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.
Relay or intermediate switches
From two places, a pair of two-way switches is simpler, and no relay is needed. From three places on, the relay wins: a 3×1.5 between push-buttons is enough, carrying only the live and the wire to the relay. Intermediate switches are chained with a 5×1.5 between every two neighbouring switches: it carries two strapper cores, neutral and earth. A new place with a relay is just one more push-button and one more length of 3×1.5, with nothing changing in the consumer unit or the back box by the door; with intermediate switches it is another intermediate and another 5×1.5. This shows most in a long hallway and on a staircase, where the cables between switches are long.
A relay also helps when you want to switch off all the lights at the entrance with one button. For this you use a relay with a central control input: a master push-button by the door switches all the groups off at once, while the local push-buttons work as usual. The interactive diagram has no central control; see the instructions for your relay for its wiring.
A relay has its drawbacks too: it takes up space in the consumer unit or the back box; the push-buttons do not show whether the light is on, because a push-button always springs back; and the push-button back boxes have no neutral, since the 3×1.5 daisy chain carries only the live and the wire to the relay.
Wiring diagrams
Relay in the consumer unit, three push-buttons
Choose this if there is free space on the DIN rail in the consumer unit: the modular relay goes next to the lighting MCB, the live from the MCB reaches terminal 1 via a short link, and neutral goes to A2. A 5×1.5 runs from the consumer unit to the back box by the door: black from the push-button ↓ to A1, brown is the live from terminal 1 to the push-button L, grey runs from terminal 2 to the light, blue is neutral, green-and-yellow is earth. Grey, blue and green-and-yellow pass through the back box on lever connectors and leave for the light in a 3×1.5 cable, the grey continuing on the brown. From the push-button by the door, a 3×1.5 daisy chain runs to the sofa and on to the hallway: brown on L, blue on ↓ (it is marked with brown tape), and the green-and-yellows are joined at the sofa with a lever connector so that earth reaches the last push-button.
Relay in the consumer unit, five push-buttons
The same circuit, with the daisy chain simply carrying on: from the hallway to the bedside and on to the place in the middle. Each new link is another 3×1.5 cable, and in each back box the chain passes through, the green-and-yellows are joined with a lever connector. Nothing changes in the consumer unit or in the back box by the door: there is still one wire to A1 for all the push-buttons. A sixth or a tenth push-button is added the same way: the relay sets no limit on ordinary non-illuminated push-buttons; the limit is the length of the line to them (up to 100 m on Busch-Jaeger, for example).
Compact relay in a back box
Choose this if there is no room in the consumer unit or running a 5×1.5 to it is awkward: the compact relay goes in a deep 60 mm back box by the door together with the push-button, and an ordinary 3×1.5 runs from the consumer unit. The brown from the consumer unit goes into a lever connector, from which short links take the live to the push-button L and to relay terminal 1, and a link runs from the push-button ↓ to A1. The blue from the consumer unit goes to A2, and the blue to the light is taken from the same terminal, while the brown to the light leaves from terminal 2. The other push-buttons are on the same 3×1.5 daisy chain from the push-button by the door: the blue on ↓ is marked with brown tape, and the green-and-yellows are joined at the sofa with a lever connector.
Common mistakes
Ordinary switch instead of a push-button
An ordinary switch was fitted by the door instead of a push-button. Switch it on and the light comes on, but the relay coil stays energised. Switch it off and the light stays on: the relay only changes over at the moment the switch is turned on, so the light responds only every other time. While the switch by the door is on, the push-buttons by the sofa and in the hallway do nothing.
Why this is wrong
An impulse relay coil is designed for a short pulse. Most modular relays do not allow the coil to be energised continuously: for the Finder 20 and 26 and the Hager EPN the instructions say no longer than an hour, otherwise the coil overheats. Even with a relay that allows a continuous signal (for example the compact Finder 27.2x), a switch changes the light over only every other time, and the other push-buttons do not work. Fit only retractive push-buttons in every place: from the outside they look just like switches, so check the name and the diagram on the device.
Push-buttons in series
The push-buttons were connected in a chain, like switches: the live goes through the push-button by the door, then the one by the sofa, then the one in the hallway, and only from the last one does it return on the brown cores to A1 on the relay. Pressing any single button does nothing. The light only changes over if you press and hold all three at once.
Why this is wrong
There is no danger, but you cannot control the light this way. Push-buttons for an impulse relay are connected in parallel: the live arrives at terminal L of each one, and the ↓ output of each goes to the common wire to A1, so any push-button closes the coil circuit on its own. In the daisy chain this means: in each back box the browns are joined on terminal L and the blues on terminal ↓, and no push-button sits in the break of the wire to the next one.
How to wire an impulse relay, step by step
Switch off the MCB
For work in the back boxes, switch off the lighting MCB, or the main switch if you are not sure which one it is. If you are fitting the relay in the consumer unit, switch off the main switch: the top terminals of the lighting MCB stay live even when it is off. 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 all the 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.
Fit the relay in the consumer unit
Clip the modular relay onto the DIN rail next to the lighting MCB. Link the MCB output to relay terminal 1, and terminal A2 to the neutral bar of the RCD section that the lighting MCB is in: a neutral from another section’s bar will trip the RCD. The 5×1.5 cable to the back box by the door: black to A1, brown also to terminal 1, grey to 2, blue to the same neutral bar, green-and-yellow to the earth bar. A compact relay goes in the back box by the door; it is wired in the next steps.
Bring in the cables and mark the cores
Three cables come into the back box by the door: from the consumer unit, to the light and to the next push-button. Back boxes along the chain take two each, from the previous push-button and to the next, and the last one takes one. Label which cable comes from where, and in each 3×1.5 cable between push-buttons wrap the blue core in brown tape at both ends: the live returns along it from the push-button to the relay.
Wire the back box by the door
With the relay in the consumer unit: the brown from the consumer unit and the brown to the next push-button go to the push-button L; the black from the consumer unit and the marked blue to the next push-button go to ↓. Use lever connectors to join the grey from the consumer unit to the brown to the light, the blue from the consumer unit to the blue to the light, and all the green-and-yellows together. With a compact relay: the brown from the consumer unit into a lever connector, from it short links to the push-button L and to relay terminal 1, and from the push-button ↓ a link to A1; the blue from the consumer unit to A2, with the blue to the light from the same terminal; the brown to the light from terminal 2; all the green-and-yellows into a common lever connector. The daisy chain to the next push-button goes on the push-button by the door: brown on L, blue on ↓.
Connect the other push-buttons and the light
On each push-button, the browns go to terminal L and the blues to ↓. In back boxes along the chain each terminal takes two cores: from the previous push-button and to the next. If a terminal will not take two wires, join them with a lever connector and run one short wire to the push-button. Do not insulate the green-and-yellows: in back boxes along the chain join both with a lever connector for 2 wires, and at the last push-button connect the end to the PE terminal of the device if it has one, otherwise insulate it. At the light: L — brown, N — blue, PE — green-and-yellow.
Check it works
Switch the MCB on and go round all the push-buttons several times: every press in any place must change the light over, and releasing must change nothing. If in some place the light only changes every other time, there is a switch there, not a push-button. If the push-buttons do nothing when pressed one at a time, they are connected in series. Switch the light off and check the lampholder contact with a tester: there must be no live there.
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. Fit the relay in the consumer unit with the main switch off: the top terminals of the lighting MCB are live even when it is off. 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 it must comply with BS 7671, and a new circuit at the consumer unit is notifiable work. 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 many push-buttons can I connect to an impulse relay?
Ordinary non-illuminated push-buttons — as many as you like: they are connected in parallel, and each one simply feeds the live to A1. The limit is the length of the line to the push-buttons, up to 100 m on Busch-Jaeger, for example. Illuminated push-buttons are different: their total current is limited, usually to 3–5 mA, which means only a few push-buttons, and for more you need a compensator or a separate neutral for the lights.
Can I connect an ordinary switch to an impulse relay?
No, only retractive push-buttons. A switch that is on keeps the coil energised, and most modular relays allow this for no longer than an hour. Besides, the light only changes over when the switch is turned on, that is every other time, and while it is on, the other push-buttons do not work.
Which is better: an impulse relay or an intermediate switch?
From two places, a pair of two-way switches, and no relay is needed. From three places on, a relay is more convenient: a 3×1.5 between push-buttons is enough, while intermediate switches are chained with a 5×1.5 between all the switches. A new place with a relay is one more push-button and a length of 3×1.5, with nothing changing in the consumer unit or the back box by the door. And a relay with a central control input also lets you switch off all the lights with one button at the entrance.
What cable do I need for impulse relay push-buttons?
Between push-buttons, 3×1.5 mm²: brown is the live to L, blue runs from ↓ back to the relay and is marked with brown tape, green-and-yellow continues the earth and is joined with a lever connector in the back boxes along the chain. With the relay in the consumer unit, a 5×1.5 runs from the consumer unit to the back box by the door; with a compact relay in that back box, a 3×1.5; and a 3×1.5 to the light. The lighting circuit is protected by a B10 MCB.