Extractor Fan Wiring Diagram

Extractor Fan Wiring Diagram — interactive diagram. Open it in the editor to customise components and wiring.

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

Complete extractor fan wiring reference for bathroom, kitchen, and utility ventilation fans covering switched, timer, overrun, and humidity-controlled configurations with terminal connections.

An extractor fan removes moisture-laden or contaminated air from bathrooms, kitchens, and utility rooms, preventing condensation, mould growth, and odour. The electrical wiring configuration depends on the control method required: simple switch, automatic timer-overrun, or humidity sensor (humidistat) triggering.

The most fundamental bathroom extractor fan wiring in a UK-type installation uses a switched live feed: the fan's live terminal receives a switched live from the bathroom light switch (so the fan runs whenever the light is on). The neutral is connected to the fan's neutral terminal, and an earth is connected to the fan's earth terminal. This three-wire connection (switched live, neutral, earth) is the starting point for all more complex configurations.

For timer-overrun operation, the fan receives two live feeds: an unswitched permanent live (L) and a switched live from the light switch (SL). When the light is turned on, SL energises the fan. When the light is turned off, the fan's internal timer keeps it running for an adjustable overrun period (typically 1–20 minutes) using the permanent live before shutting off. This is the most common UK bathroom installation and is required by Part F of the Building Regulations where fan-on-light switching is used.

Humidity-controlled fans incorporate an internal humidistat sensor. The fan starts automatically when relative humidity exceeds a set threshold (typically 70–85 % RH) regardless of light switch status. These fans require a permanent live, neutral, and earth only — no switched live — because the humidistat provides internal switching. Optionally, a switched live can be added to allow manual override.

In all cases, wiring must comply with BS 7671 (IEC 60364) and, for bathroom installations, must observe the bathroom zones (IP rating requirements) specified in BS 7671 Part 7, Section 701. Extractor fans must be installed within Zone 2 or outside all zones, and must carry the appropriate IP rating for their location.

An extractor fan with a built-in or separate timer adds a post-run delay function, allowing the fan to continue extracting moisture for a set period after the lights are switched off. Wiring a timer extractor fan correctly requires understanding the live, neutral, and switched-live connections, as well as the separate timer terminal (often labelled T or O/P) that keeps the fan running after the switch opens. Requirements differ between fans that take their timer supply from the switched live versus a permanent live, so always consult the fan's wiring diagram. Use Circuit Diagram Maker's free browser tool to plan your installation before connecting any cables.

How to wire extractor fan wiring diagram

Determine the required control configuration Decide whether the fan will be: (a) switched with the light only; (b) switched with the light but with an overrun timer; (c) humidity-controlled (automatic); or (d) independently switched. This determines the number of conductors required in the wiring — 2-core+earth for humidity-only; 3-core+earth for timer-overrun or independent switching.
Isolate the circuit at the consumer unit and verify dead Turn off the relevant circuit breaker at the consumer unit (for a bathroom fan, typically the bathroom lighting circuit or the dedicated fan circuit). Use a calibrated non-contact voltage tester and a multimeter to verify that all conductors at the installation point are de-energised before working.
Route and prepare the supply cable Run the correctly sized cable (1.0 mm² or 1.5 mm² 2-core+earth, or 3-core+earth as required) from the supply point (lighting circuit junction box, FCU, or consumer unit) to the fan position. For ceiling installations, use appropriate cable clips or containment. In bathrooms, follow IEC 60364 / BS 7671 zone requirements for cable routing.
Connect the fan terminals Open the fan's terminal cover. Connect conductors to the terminals marked on the fan: L (permanent live) — brown conductor from the fused supply; SL (switched live, if fitted) — the brown conductor from the switch; N (neutral) — blue conductor; Earth — green-and-yellow conductor to the earth terminal or chassis point. If the fan has only L and N terminals (no SL), connect the switched live to L.
Set the overrun timer or humidistat (if applicable) For timer fans, adjust the internal overrun timer potentiometer to the required duration (typically 5–15 minutes for a bathroom). For humidity-controlled fans, set the humidistat threshold level using the sensitivity adjustment (typically set to trigger at 70–80 % relative humidity). Refer to the fan's installation manual for the specific adjustment procedure.
Secure the fan in the installation aperture Mount the fan in the ceiling or wall aperture according to the manufacturer's instructions. Ensure the fan is mechanically secure and the duct connection is airtight. In timber-framed constructions, use the fan's fixing brackets to span between joists rather than relying only on the plasterboard.
Restore power and test operation Re-energise the circuit. Test all control modes: operate the light switch and verify the fan starts; for timer fans, switch off the light and verify the fan continues for the set overrun period before stopping; for humidity fans, breathe near the sensor or temporarily cover it to simulate high humidity and verify the fan starts. Verify air discharge through the external vent.

Specifications

Supply voltage	230 V AC, 50 Hz (UK/EU standard)
Typical motor power consumption	15–30 W (axial ceiling fan); up to 60 W (centrifugal inline fan)
IP rating — Zone 1 (above bath/shower to 2.25 m height)	Minimum IP45 (BS 7671 Section 701)
IP rating — Zone 2 (600 mm horizontal from bath/shower edge)	Minimum IP44 (BS 7671 Section 701)
Minimum ventilation rate (bathroom, intermittent, UK Part F)	15 litres per second (54 m³/h)
Minimum ventilation rate (kitchen, intermittent, UK Part F)	30 litres per second (108 m³/h) adjacent to hob; 60 l/s elsewhere
Timer overrun range (typical)	1 to 20 minutes (adjustable via internal potentiometer)
Humidistat trigger range (typical)	60–90 % relative humidity (adjustable)

Safety warnings

Always isolate the circuit at the consumer unit and verify dead with a calibrated voltage tester before working on any fan wiring. Bathroom circuits often share live conductors between lighting and fan wiring — verify all conductors are de-energised, not just one.
Bathroom extractor fans must comply with the IP rating requirements of BS 7671 Section 701 (IEC 60364-7-701) for the zone in which they are installed. Installing a fan with an insufficient IP rating in a bathroom zone is a code violation and presents a risk of electric shock from water ingress.
Do not connect bathroom extractor fans to a standard socket-outlet on a ring or radial circuit without fusing. Use an FCU (fused connection unit) with a 3 A fuse to provide both isolation and appropriate overcurrent protection for the fan wiring and motor.
Extractor fan ductwork must be routed to discharge outside the building — not into a roof void, loft, or ceiling cavity. Discharging moist air into a confined space causes condensation, structural timber decay, and mould. External grilles must include a backdraught shutter to prevent wind-driven air ingress.
All fixed electrical work in bathrooms and kitchens must be notified under Part P of the Building Regulations (England and Wales) or the equivalent in other jurisdictions, unless carried out by a registered competent person. Work must comply with BS 7671 and be accompanied by an Electrical Installation Certificate.

Tools needed

Insulated screwdrivers (flat-blade 2.5 mm and 5 mm for terminal connections)
Calibrated non-contact voltage tester and multimeter
Hole saw or jigsaw (for cutting ceiling or wall aperture to fan dimensions)
Cable stripper for 1.0 mm² and 1.5 mm² conductors
Drill with extension for ceiling work
Duct cutter and duct tape (for flexible duct connection)
Torque screwdriver (where terminal torque is specified in installation manual)

Common mistakes

Connecting the permanent live and switched live to the wrong terminals — swapping L and SL means the fan runs only on the timer and never responds to the light switch (or vice versa, depending on the fan's internal circuit).
Using 2-core+earth cable where 3-core+earth is required for timer-overrun fans — without a separate permanent live, the timer cannot function after the switch opens.
Not fitting a backdraught shutter on the external grille — without a shutter, wind pressure causes cold air to blow back through the fan and into the room, dramatically reducing ventilation effectiveness and causing heat loss.
Failing to verify the IP rating of the chosen fan for the bathroom zone — a fan rated IP20 is not suitable for any bathroom zone; IP44 minimum is required in Zone 2.
Incorrectly positioning the external discharge grille — discharging into an adjoining cavity, roof void, or within 300 mm of an openable window or door causes moisture problems and does not satisfy Building Regulations ventilation requirements.

Troubleshooting

Fan runs continuously and does not switch off: Cause: Timer overrun duration set too long, humidistat threshold set too low (fan keeps triggering), or the switched live terminal is permanently live (connected to unswitched live instead of light switch output) Fix: Check the overrun timer setting and reduce if necessary. For humidity fans, increase the humidistat threshold. Verify that the SL terminal is receiving a switched live that drops to zero when the switch is off, using a multimeter.
Fan does not start when light is switched on: Cause: No switched live reaching the fan (broken conductor, loose terminal, or wrong terminal connected), blown internal motor capacitor, or failed fan motor Fix: With the light switch on, measure voltage at the fan's SL (or L) terminal. If 230 V is present and the fan does not start, the fan has an internal fault (motor or capacitor). If no voltage is present, trace the switched live circuit back to the light switch to find the break or wrong connection.
Fan is noisy or vibrating excessively: Cause: Fan body not secured properly in the aperture, ductwork vibrating against structure, fan wheel obstructed by debris, or worn fan bearings Fix: Verify all mechanical fixing screws are tight. Inspect the impeller for debris or obstruction. Check ductwork is properly supported and not in direct contact with structure at rigid spans. If bearings are worn, the fan should be replaced — motor bearings in extractor fans are not typically serviceable.

Frequently asked questions

What wiring does a basic extractor fan need?

A basic switched extractor fan needs three conductors: a switched live (from the light switch, so the fan runs when the light is on), a neutral, and an earth. The switched live and neutral connect to the fan's L and N terminals; the earth connects to the earth terminal or the fan body earth point.

What is an overrun timer on an extractor fan and how is it wired?

An overrun timer keeps the fan running for a set period after the light switch is turned off, to clear residual moisture. It requires two live conductors: a permanent live (always energised from the supply) and a switched live (from the light switch). When the switch opens, the timer uses the permanent live to run the fan for the overrun period.

Can I wire an extractor fan to its own separate switch?

Yes. In rooms outside bathrooms (kitchens, utility rooms) a standard light switch or double-pole isolator can control the fan independently from the lighting. In bathrooms, the switch must be located outside the room or be a pull-cord switch, unless it is a low-voltage switch or SELV switch located within the bathroom zones.

What IP rating does a bathroom extractor fan need?

Under BS 7671 Section 701, Zone 1 (above bath/shower to 2.25 m) requires minimum IP45. Zone 2 (within 600 mm horizontally from bath/shower edge) requires minimum IP44. Outside all zones (e.g. ceiling above the door) requires IP21 minimum. Always verify the fan's declared IP rating matches the installation zone.

Does an extractor fan need a fused connection unit (FCU)?

In the UK, extractor fans are commonly connected via a fused connection unit (FCU) or spurred from the ring final or radial circuit, rather than via a plug and socket. The FCU provides a local isolation point (its built-in switch) and fusing — typically a 3 A fuse — to protect the flex. This is best practice for permanently connected fans.

How do you wire an extractor fan with a timer?

Most timer extractor fans have three or four terminals: a permanent live (L), neutral (N), a switched live from the lighting circuit (SL), and sometimes a separate timer output. Connect permanent live and neutral from the supply; connect the switched live to the SL terminal so the fan starts when the light is on. When the light is switched off, the fan's internal timer keeps it running (typically 1–20 minutes, adjustable) via its own internal relay before cutting out. On fans that derive the timer supply from the permanent live only, you still need a two-core and earth plus a single switched live cable run to the fan — check the manufacturer's wiring diagram as the terminal arrangement varies by model.

Related diagrams

Free electrical calculators

Edit this diagram free in the online editor