In short: wiring a wired intercom means linking a door station, mounted outside, to an indoor unit, then powering the whole system through an extra-low-voltage transformer. The job always starts by switching off the power at the consumer unit. The hard part is mostly running the cables between the house and the gate, and following the manual’s wiring diagram when connecting.
Wiring an intercom is within reach of a careful DIYer, provided the steps come in the right order: prepare the work area with the power off, run the cables, connect the terminal blocks following the manufacturer’s diagram, then test before filling in. This guide details each step for a wired audio or video intercom, the most common setup in a detached house, without targeting any brand or model.
Wiring an intercom at a glance
| Step | What to do | Watch out for |
|---|---|---|
| Switch off the power, pick the locations | Check that no voltage remains |
| Choose the cable for the distance | Conduits separate from 230 V |
| Wall chases, trench or trunking | Suitable conduit if buried |
| Door station, monitor, strike | Respect the polarity |
| Power on and try every function | Fill in only after the test |
Summary of the installation guides reviewed on 20 October 2026. The manufacturer’s manual always takes precedence.
How a wired intercom works
An intercom has two parts linked by a cable. Outside, the door station carries the call button, a microphone, a speaker and, on a video intercom, a small camera often paired with night lighting. Inside, a handset (audio intercom) or a monitor (video intercom) receives the call and lets you talk to the visitor.
The system runs on extra-low voltage. A transformer steps the home’s 230 V down to the voltage the device needs, which varies between manufacturers (12, 15, 17 or 24 V depending on the models quoted in the guides reviewed). This transformer is either built into the indoor unit or separate, often as a module that clips onto a rail in the consumer unit.
The indoor unit can also control an electric door strike, an electric lock or a gate motor. Recent so-called connected intercoms add a Wi-Fi link that forwards the call to a smartphone, a use close to that of a smart doorbell, covered in the video doorbells section.
The tools and cable you need
Before starting, gather everything you need so the job is not left half done. The guides reviewed list simple tools: a drill and bits suited to the wall, screwdrivers, wire strippers, a spirit level, a tape measure, wall plugs and screws. To recess the wires, add a wall chaser or a chisel and lump hammer, then filler or plaster to make good.
The choice of cable depends mainly on the distance between the door station and the indoor unit. The longer the run, the larger the cross-section must be to avoid losses.
| Door station to indoor unit | Recommended cross-section | Wire type |
|---|---|---|
| Up to about 25 m | Around 0.75 mm² | Thin telephone-type wire |
| Beyond 25 m | 1.5 mm² | Standard electrical wire |
Values taken from the installation guides reviewed on 20 October 2026. Some manufacturers require a specific cable: the manual takes precedence.
One last point matters from the moment of purchase: the intercom cable must not share a conduit with a 230 V circuit. The guides flag this as a source of interference, hence the use of separate conduits for extra-low voltage.
Preparing the job safely
Switch off the power before any work
The first step allows no exception: switch the line off at the consumer unit before touching a wire, then check that no voltage remains with a suitable tester. If a power tool is needed during the job, plug it into a socket on another circuit using an extension lead. The intercom’s power supply is only switched on once every wire is connected. If in doubt about the existing installation or the connection to the consumer unit, calling an electrician remains the safest route.
Choose where the door station and indoor unit go
The door station is fixed on a gate pillar, or next to the front door when it opens straight onto the street. Recommended heights vary between manufacturers, generally between 1.20 m and 1.75 m. For a video intercom, several guides suggest thinking in terms of the camera lens height, around 1.60 m, to frame a visitor’s face. Avoid a camera facing due south, into the sun, which would make the picture unreadable; failing that, a hood reduces glare.
The indoor unit usually goes in the hallway, between 90 and 130 cm from the floor for comfortable use. Placing it near the consumer unit or an old doorbell makes the power supply much simpler.
Running the cables from the house to the gate
Routing the wires is often most of the work. Two runs need planning: from the power source to the indoor unit, then from the indoor unit to the door station. The guides advise measuring each run and adding about twenty centimetres at each end for the connections. Labelled tape on each wire avoids mix-ups when connecting.
Inside the home
Indoors, the wires run in trunking or in a wall chase. In the second case, the chase is cut to the right depth, the conduit is held in place at intervals, then the chase is cleaned before filling. That filling only happens after the working test.
Outside, between the facade and the gate
Outside, the cables can run in a rigid tube fixed to the wall or be buried. Burying them requires a trench in the garden and chases in the facade and the pillar. The French guides point out that outdoor electrical installations fall under the NF C 15-100 standard: buried conductors in ICTA-type conduit, red warning mesh along the whole length of the trench and a minimum depth to respect, greater under a driveway than under a footpath. The conduit sits on a bed of sand before backfilling. Over a long distance, hiring a trencher saves a lot of time.
Connecting the door station and the monitor
Follow the wiring diagram in the manual
Each device has one or more numbered terminal blocks. The indoor unit often has two: one for power, one for the link to the door station. The rule is simple and non-negotiable: follow the wiring diagram in the manual, terminal by terminal. On a 2-wire video intercom, this cable carries both power and video, and it is usually polarised. Reversing it stops the device from working; some models have reverse-polarity protection, which saves the circuit board without removing the need to fix the wiring. 230 V must never reach the monitor directly: it always goes through the supplied transformer.
On the street side, the wires enter through the cable gland in the door station’s base, then connect to the terminal block. A bead of silicone on the back of the door station, recommended by several guides, helps rainwater run off the sides instead of seeping in.
Replacing an old doorbell
When the intercom replaces a doorbell, its wires can be reused if they are in good condition and of a suitable cross-section. Remove the chime while noting the two power wires (live and neutral) and the two wires from the push button, then extend them to the indoor unit with connectors placed in a junction box, recessed or surface-mounted.
Connecting the door strike or a motorised gate
The electric door strike connects to the dedicated terminals of the door station or the indoor unit, according to the diagram. For a motorised gate, control usually goes through a dry contact, linked to the intercom’s designated terminals and to the matching input of the gate motor. Compatibility between the two devices is checked in both manuals before starting.
Powering up and testing the intercom
One tip comes up among specialist retailers: do a bench test before mounting the door station, with a short length of cable a few metres long, to spot a fault out of the box and get used to the device. Once the system is in place, the power goes back on and every function is tried one by one: a call from the street, sound quality, the picture on the monitor, opening the strike or the gate.
A function that does not respond means switching the power off again and rechecking the connections wire by wire, starting with polarity. Only after this test are the chases filled and the trench backfilled. On a connected model, the Wi-Fi setup and the app are configured at this stage. Where useful, a camera nicely complements the setup to watch the driveway or the gate: the outdoor security camera comparison reviews wired, battery and solar options.
Wireless intercoms and flats: special cases
A wireless intercom avoids all the cabling between the street and the house: the door station and indoor unit communicate by radio, and the door station often runs on batteries. The guides reserve it for short distances, around 10 metres, beyond which a wired model is recommended. The range quoted by manufacturers applies in open field; walls, hedges and other wireless devices reduce it. A model that runs over Wi-Fi depends on the quality of the network: the guide on how many Mbps for good Wi-Fi helps estimate the speed needed. In a block of flats, filming common areas falls under other rules, covered in the guide to home security camera rules in France.
In a block of flats, the door station and the wiring in the common areas belong to the co-ownership. The occupant of a flat normally only works on the indoor unit in their own home, and it is best to check with the building manager before any change. To equip the rest of the home with connected devices, the smart home section gathers the site’s guides.