4 Wire Doorbell Wiring Diagram

4 Wire Doorbell Wiring Diagram — interactive diagram. Open it in the editor to customise components and wiring.

This is a free printable 4 wire doorbell wiring diagram: download the diagram as SVG or open it and print to paper or PDF.

A 4 wire doorbell wiring diagram covers systems with a front door button, rear door button, and a chime unit that plays different tones per button — or a basic intercom system using a 4-conductor run.

A standard residential doorbell system uses a low-voltage transformer (typically 8–24 V AC in North America; 8–12 V AC in the UK and Europe) to power the chime unit and button circuits. A basic 2-button, 1-chime system — the most common use case for 4-wire wiring — uses the four conductors as follows:

- Wire 1: Transformer secondary output to the chime unit (common live supply terminal, often labelled 'TRANS' or 'T') - Wire 2: Front door button return from chime to front button, then onward to front button and back - Wire 3: Rear door button circuit, similar to Wire 2 but for the rear or side entrance - Wire 4: Common return (neutral) back to the transformer secondary

Alternatively in a simpler 4-wire layout: the transformer feeds the chime, the chime has three button terminals (Front = 'FRONT', Rear = 'REAR', Common = 'TRANS'), and the four wires are: common supply to chime, front button wire out to front button, rear button wire out to rear button, and a shared return (common) running back to the transformer from the button side. The button simply closes a circuit between its two terminals when pressed.

Most chime units play a distinct tone for the front door (typically two-note 'ding-dong') and a single note for the rear door, allowing occupants to identify which entrance is being used.

For modern smart doorbells (video doorbells) that replace a front-door button, most require only 2 of the 4 wires — the existing transformer supply and return. The additional wires are unused, but the 4-wire run provides upgrade flexibility.

For a basic intercom system (which also commonly uses 4 conductors): the four wires carry a 2-wire audio circuit (TX and RX, or a single shared audio pair for simplex intercom), a door-release circuit, and a common/ground. True intercoms with multiple stations, camera feeds, or duplex audio typically require more than 4 conductors or a network connection.

How to wire 4 wire doorbell wiring diagram

Locate and test the doorbell transformer Find the existing transformer (typically near the consumer unit, in a loft, or mounted on a junction box). Measure the secondary output voltage with a multimeter set to AC volts — confirm it matches the chime unit and (if applicable) video doorbell specification. Measure under load (with the chime circuit connected) as well as no-load, as a weak transformer will show voltage drop under load.
Plan the 4-wire routing Plan the route from the transformer location to the chime (typically in a hallway) and from the chime to each button location. For a two-button system (front and rear), the most efficient 4-wire layout runs a single 4-core cable from the transformer through to the chime, with branches to each button. Alternatively, two separate 2-core runs from the chime to each button, plus 2-core from transformer to chime, uses 6 cores total but may be simpler to route.
Connect the transformer to the chime unit Run the first two wires (of the 4-core cable) from the transformer secondary terminals to the chime TRANS terminal (one wire from each secondary terminal, polarity does not matter for AC). At the chime, connect one wire to TRANS and the other to the common return terminal (sometimes unlabelled or marked as the second TRANS terminal on dual-supply chimes).
Wire the front door button Run one wire (Wire 3 of 4) from the chime FRONT terminal to one terminal of the front door button. Run Wire 4 from the other terminal of the front button back to the common return point (typically the same return wire that runs back to the transformer secondary). When the button is pressed, it completes the circuit: transformer → chime FRONT terminal → button → common return → transformer.
Wire the rear door button For a 4-wire system covering two buttons, use the remaining two wires (or a second 2-core run) for the rear button in the same manner: chime REAR terminal → rear button → common return. Verify the chime's REAR terminal exists and is operational — some low-cost chimes support only a single button.
Test both buttons before closing up Restore power to the transformer. Press the front button: the chime should play its front-door tone (typically two notes). Press the rear button: the chime should play its rear-door tone (typically one note). Both buttons should produce distinct and clear sounds. If a button produces no sound, check the wiring path from the chime terminal through the button to the common return.

Specifications

Transformer secondary voltage (North America typical)	16 V AC (also 8 V and 24 V variants available)
Transformer secondary voltage (UK/Europe typical)	8–12 V AC
Standard chime supply requirement	8–24 V AC at 5–15 VA depending on model
Video doorbell power requirement (typical)	16–24 V AC, 20–40 VA (check manufacturer specification)
Bell wire gauge (North America)	18 AWG, 2-core or 4-core
Bell wire gauge (UK/Europe)	0.5 mm², 2-core or 4-core
Front door button IP rating (outdoor)	IP44 minimum (BS EN 60529); IP65 recommended for exposed locations
Applicable guidance	NEC / NFPA 70 Article 725 (Class 2 and Class 3 remote-control circuits); BS 7671 Part 7 (special installations)

Safety warnings

This diagram is for reference and educational purposes only. While the doorbell secondary circuit is low voltage (typically 8–24 V AC) and not immediately life-threatening, the transformer primary circuit is connected to mains voltage (120 V AC or 230 V AC). Working on or near the transformer primary connections requires isolation of the mains supply and verification with a calibrated voltage tester. In many jurisdictions, connection of the transformer to the mains supply must be performed by a licensed electrician.
Do not use doorbell bell wire (18 AWG / 0.5 mm²) for any mains-voltage circuit. Bell wire is rated for low-voltage use only and is not suitable for mains wiring. Keep low-voltage doorbell wiring physically separated from mains cables at all times.
Ensure any outdoor button installation uses a pushbutton with an appropriate ingress protection rating for the local climate. A button with inadequate sealing will allow moisture ingress that corrodes the contacts and can short the doorbell circuit, causing the chime to ring continuously or the transformer to overheat.
Verify the transformer is fused or the circuit is protected at the distribution board. A direct short across the doorbell wiring (e.g. from cable damage) with an unprotected transformer can cause the transformer secondary winding to overheat. Most proprietary doorbell transformers have internal thermal protection.
For smart video doorbells requiring higher current (1–2 A), verify the transformer VA rating is adequate before connecting. An undersized transformer running at sustained overload will overheat and fail — in some cases causing a fire risk at the transformer mounting point.

Tools needed

Digital multimeter (AC voltage setting for transformer output measurement)
Non-contact voltage tester (for verifying mains is isolated before transformer work)
Insulated flat-blade and cross-head screwdrivers for chime and button terminal connections
Wire strippers matched to bell wire gauge (18 AWG / 0.5 mm²)
Cable staple gun or clips for routing bell wire
Continuity tester or multimeter in continuity mode for tracing bell wire runs
Drill and bits for button mounting into door frame or masonry
Fish tape or cable rods for routing wire through wall cavities

Common mistakes

Wiring both buttons to the same chime terminal (FRONT), so pressing either button triggers the same tone and the chime cannot distinguish between front and rear entries.
Omitting the common return wire and attempting to use the earth conductor as a return — the doorbell earth is a safety earth and must not carry circuit current.
Connecting bell wire to the mains-side terminals of the transformer rather than the low-voltage secondary terminals, resulting in mains voltage on the button wiring — an electrocution hazard.
Using a transformer with insufficient VA rating for a video doorbell, causing the doorbell to drop out during high-current events (motion recording, two-way audio) and displaying incorrect 'low power' warnings.
Routing bell wire through the same conduit or cable duct as mains wiring, which is a regulatory violation under most wiring codes and can cause interference on the doorbell circuit.
Installing a surface-mount front door button without weather sealing in a location exposed to rain, leading to corrosion of the contacts and intermittent or permanent fault within one or two seasons.

Troubleshooting

Pressing the front button produces no chime sound: Cause: Open circuit in the front button wiring loop, failed button contact, incorrect wiring at the FRONT terminal, or insufficient transformer voltage under load Fix: Disconnect the chime. Use a multimeter to measure resistance between the wire from the FRONT terminal and the common return wire — pressing the front button should show near-zero resistance (closed circuit) and open circuit when released. If the circuit reads open when pressed, the button contact has failed. If resistance is correct at the button, trace the wiring back to the chime terminal for open connections.
Chime sounds continuously without any button being pressed: Cause: A button contact is jammed closed (debris or corrosion), the button wiring has a short circuit somewhere in the run, or the chime plunger mechanism is stuck in the energised position Fix: Temporarily disconnect the button wires from the chime terminals one at a time. When the continuous sounding stops, the disconnected circuit is the source of the short. Trace that circuit: inspect the button for jammed or corroded contacts, and check the wire run for insulation damage or pinched conductors causing a short.
Smart video doorbell shows low power or offline notification: Cause: Transformer output voltage drops under the video doorbell's operating current demand, indicating an undersized transformer Fix: Measure transformer output voltage at no load and then at full load (with the doorbell actively streaming). A voltage drop of more than 10–15% indicates the transformer is too small. Replace the transformer with a higher VA rating specified by the doorbell manufacturer — many modern video doorbells specify a minimum 16 V AC at 30 VA or higher.

Frequently asked questions

What voltage does a residential doorbell transformer output?

In North America, most residential doorbell transformers output 16 V AC (the most common), 8 V AC, or 24 V AC. In the UK and Europe, 8–12 V AC is typical. The transformer is usually located in the distribution board (UK) or near the main panel (North America), or mounted on an accessible junction box. Always verify the voltage with a multimeter before wiring the chime, as chimes are rated for specific voltages.

How do I wire a two-button doorbell with different chimes for front and rear doors?

Connect the transformer output to the chime's TRANS terminal. Connect a wire from the chime's FRONT terminal to the front door button; the other button terminal returns to the transformer (via the common wire). Repeat for the rear door, connecting from the chime's REAR terminal. When the front button is pressed, it completes the circuit through the FRONT terminal and triggers the two-note chime. When the rear button is pressed, it completes the circuit through the REAR terminal and triggers the single-note chime.

Can I use existing doorbell wiring for a smart video doorbell?

Typically yes, if the existing transformer provides sufficient voltage and current for the video doorbell. Most wired video doorbells require 16–24 V AC at a minimum of 500 mA (check the product specification). A 10 VA or 16 VA transformer may not provide enough current — video doorbells can draw 1–2 A or more. A transformer upgrade may be required. Only two of the four wires are typically used for the smart doorbell itself.

Why does my doorbell chime sound faint or buzzy?

Faint chime typically indicates a low supply voltage — check transformer output voltage under load. A buzzy or humming chime (where it hums continuously rather than chiming) usually indicates a stuck button, a stuck chime plunger, or a wiring short holding the button circuit permanently closed. A stuck plunger in a mechanical chime can be freed by gently pressing it by hand.

What cable should I use for doorbell wiring?

18 AWG (North America) or 0.5 mm² (UK/Europe) 2-core or 4-core bell wire is the standard for doorbell wiring. Bell wire is not rated for mains voltage and must only be used in the low-voltage secondary circuit of the doorbell transformer — never on the primary (mains) side. For outdoor runs, use UV-rated outdoor bell wire or route through conduit.