Access control wiring diagram
Reader, controller, strike or maglock, power supply: the block diagram of a door and the wiring rules.
An access-controlled door is always the same assembly: a reader, a controller that decides, a locking device, a few inputs and a battery-backed power supply. Here is the block diagram and the wiring rules that apply to most installations.
This guide gives general principles. The exact diagram, terminals and wire colours depend on each device: always follow the manufacturer's manual. See the installation manuals.
The block diagram of a door
| Component | Role | Connects to |
|---|---|---|
| Card reader | Reads the credential or the phone and sends the identifier. | A reader port of the controller, in Wiegand or RS-485 (OSDP). |
| Controller | Checks the credential against the access rights and commands the opening. | The management software, over the IP network or an RS-485 bus. |
| Strike or maglock | Keeps the door locked and releases it on command. | A relay output of the controller and the power supply. |
| Exit button | Requests the opening from the inside. | A controller input. |
| Door contact | Tells whether the door is open or closed: door forced, door held open. | A controller input. |
| Manual call point | Releases the door in an emergency, without going through the controller. | In series on the power feed of the locking device. |
| Battery-backed power supply | Powers the whole door and switches to battery in the event of a power failure. | The mains, the controller and the locking device. |
The link between the reader and the controller
Wiegand
- Two data wires, D0 and D1, a common ground and the reader's power; extra wires for the LED and the buzzer.
- Point-to-point link: one reader per controller port.
- The reader talks, the controller listens: the link is neither encrypted nor supervised.
- Typical range of about 120 metres, depending on the cable.
RS-485 with OSDP
- A twisted pair for data, A and B, and the reader's power.
- Two-way link: the controller polls the reader and detects whether it is disconnected or replaced.
- Secure Channel encrypts the exchanges with AES-128.
- RS-485 range up to about 1,000 metres, with a termination resistor.
For a new installation, we recommend the OSDP link with Secure Channel. See why on the Access control security page.
The locking device: fail-secure or fail-safe
| Type | Without power | Relay contact used |
|---|---|---|
| Fail-secure electric strike | The door stays locked. It opens when the strike is powered. | Normally open (NO). |
| Fail-safe electric strike | The door is free. It is locked as long as the strike is powered. | Normally closed (NC). |
| Electromagnetic lock (maglock) | The door is free. It is held as long as the maglock is powered. | Normally closed (NC). |
- Protect the relay. A DC-powered coil produces a voltage spike when switched off: fit a flyback diode in parallel, as close as possible to the strike or the maglock, unless the manufacturer states that protection is already built in.
- Emergency exit. On an emergency exit, the manual call point cuts the power to the locking device directly, without relying on the controller. Requirements vary with the type of building: check the fire safety regulations that apply to your site.
Power supply
- Add up the current draw. Controller, readers and locking devices: the power supply must deliver the total with a margin, at the right voltage (12 V or 24 V DC depending on the equipment).
- Plan the battery. A battery-backed power supply keeps the door in service during a mains failure; its battery is sized for the backup time you need.
- Watch the voltage drop. Over a long run, a wire that is too thin lowers the voltage at the end of the cable: use a larger cross-section or move the power supply closer.
- Separate if needed. A maglock or strike that draws a lot of current is better off with its own power supply, so that it does not disturb the electronics.
See battery-backed power supplies
Wiring rules
- Shielded cable for readers, with the shield earthed at one end only, on the controller side.
- Twisted pair for RS-485, with A and B on the same pair.
- Away from mains wiring: no shared route with power cables.
- Tamper protection: connect the tamper contact of the reader and of the enclosure when the controller supports them.
- Secure side: the controller, the power supply and the relays go inside the protected area, never on the outside.
- Label the cables and keep the installation diagram with the manual.
The exact diagram for your equipment
Each controller and each reader has its own terminal block and wire colours. We provide the installation manuals of the equipment we distribute, and we help you choose components that work together.
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Guide written in November 2026. It replaces neither the manufacturer's manual nor the safety rules that apply to your building.