Bathroom Fan Wiring Diagram

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

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

Wire a bathroom exhaust fan correctly — covering the combined fan and light unit, isolation requirements, timer or humidity-sensor switching, and how to meet electrical safety regulations in wet areas.

A bathroom exhaust fan serves two purposes: removing moisture-laden air to prevent mould and structural damage, and in many combined units, providing general or task lighting. The wiring circuit must account for both functions, plus the mandatory safety requirement that no standard switched socket outlet or exposed switching device is permitted within a bathroom zone where water contact is possible.

In a typical combined fan-and-light unit, there are three separate switching requirements: an on/off switch for the light, a separate control for the fan, and — increasingly mandatory under modern building regulations — an overrun timer or humidity sensor that keeps the fan running for a set period after the light is extinguished. Some jurisdictions require the fan to be mechanically interlocked with the light, others require it to be independently switched but with a minimum 15-minute overrun.

The circuit originates at the consumer unit (distribution board) on a dedicated 6 A MCB (miniature circuit breaker) for a standard combined fan/light unit rated below 1400 W total, though in practice the load is far smaller. The circuit is typically a radial spur off the lighting circuit, run as 1.0 mm² twin-and-earth (or 1.5 mm² in some jurisdictions). Cable must be suitable for the zone — bathroom zones are defined differently by IEC 60364-7-701 (and equivalent national standards such as BS 7671 Part 7, AS/NZS 3000, or SANS 10142-1) with Zone 0 being inside the bath or shower basin, Zone 1 above the basin, and Zone 2 extending outward.

An isolator switch — a double-pole pull-cord type within Zone 1 or 2, or a wall switch outside the bathroom — must be fitted to allow safe maintenance. The pull-cord isolator switches both live and neutral simultaneously, which is an important safety feature that a single-pole switch does not provide.

Timer switches designed for bathroom use are typically electronic rotary overrun timers rated for inductive loads (motor loads behave differently to resistive loads — always use a timer rated for motors).

All metallic parts in the bathroom, including the fan housing if metal, require equipotential bonding to the earthing system. Earth continuity in the fan circuit is mandatory regardless of whether the fan body is plastic.

A bathroom fan wiring diagram often needs to show both the extractor fan and the light on the same circuit, whether controlled by a single switch, two separate switches, or a timer. Codes in many countries require the fan to run on for a set period after the light is switched off, which means the diagram must include a time-delay module wired between the switch and the fan motor. You can draft any of these configurations free in the browser circuit diagram maker without installing any software.

How to wire bathroom fan wiring diagram

Confirm the work is within the competence of a licensed or registered electrician In most jurisdictions, bathroom electrical work constitutes 'notifiable work' under electrical safety regulations (for example, Part P in England and Wales, BS 7671 in the UK, SANS 10142-1 in South Africa, AS/NZS 3000 in Australia and New Zealand). This means the work must be carried out by a qualified electrician or formally notified to the building authority. Do not proceed without confirming your local regulatory requirements.
Isolate the circuit at the consumer unit and verify dead Switch off the MCB feeding the bathroom lighting circuit. Lock or tag it out if possible. Use a non-contact voltage tester or a proving unit to confirm the circuit is dead at the intended installation point before any cable work begins. Never rely solely on switching off a circuit — always verify dead independently.
Determine zone classification for the installation position Measure the horizontal and vertical distances from the bath or shower basin to the intended fan and switch positions. Categorise each position as Zone 0 (inside the basin), Zone 1 (within 0.6 m or 1.2 m depending on jurisdiction above the basin or within the shower), or Zone 2 (outside Zone 1). Fan units must have appropriate IP ratings for their zone. Switches must comply with zone requirements as described above.
Run cable from the consumer unit or lighting spur to the fan position Use correctly rated twin-and-earth cable (1.0 mm² or 1.5 mm² depending on load and circuit length). Route cable to avoid contact with plumbing pipework or insulation batts that could cause overheating. In ceiling voids, sleeve the cable in conduit where it passes near structural members or where it could be disturbed by future insulation work. Ensure the earth conductor is sleeved in green-and-yellow sheathing at all termination points.
Install the double-pole pull-cord isolator (if required) The pull-cord isolator connects in the ceiling above the fan position — its double-pole design disconnects both live and neutral simultaneously. Run a 3-core flex from the isolator to the fan unit. The isolator provides a local means of safe isolation for maintenance without requiring a trip to the consumer unit.
Connect the fan unit following the manufacturer's terminal diagram Most combined fan/light units have separate terminal blocks for the fan motor (typically switched live, neutral, earth) and the light (switched live, neutral, earth). Some units have a separate terminal for the timer or humidity sensor control. Follow the unit-specific diagram exactly. Connect earth to the earth terminal in the fan housing even if the housing is plastic.
Test, verify, and certify the completed installation Restore power at the consumer unit. Test fan and light switching through all operating modes. If an overrun timer is fitted, confirm it runs on after the switch is turned off and stops after the set period. Record the installation with an Electrical Installation Certificate or equivalent documentation as required by local regulations. An RCD test on the circuit is recommended where an RCD is fitted.

Specifications

Typical circuit protection (MCB)	6 A Type B MCB for fan/light combination up to 1 400 W (in practice, fan loads are typically 20–100 W)
RCD protection threshold	30 mA (mandatory for bathroom circuits in most jurisdictions following IEC 60364, BS 7671, or equivalent)
Minimum cable size	1.0 mm² twin-and-earth (230 V AC); some jurisdictions require 1.5 mm² minimum
Fan zone IP rating requirement	Zone 1: IPX4 minimum; Zone 2: IPX4 minimum (confirm per applicable national standard)
Overrun timer range	Typically adjustable 5–30 minutes; 15 minutes is a common default setting
Supply voltage	230 V AC 50 Hz (UK, EU, Australia, South Africa); 120 V AC 60 Hz (North America — verify unit rating)
Applicable standards	IEC 60364-7-701; BS 7671 Part 7 (UK); AS/NZS 3000 (Australia/NZ); SANS 10142-1 (South Africa); NFPA 70 (USA)

Safety warnings

Bathroom electrical work is classified as notifiable or restricted work in most jurisdictions (including those following BS 7671, AS/NZS 3000, NEC/NFPA 70, IEC 60364, or SANS 10142-1). It must be carried out by a licensed or registered electrician and may require building authority notification or inspection. Do not attempt this work without confirming your local regulatory requirements.
Always isolate the circuit at the consumer unit and verify dead with a suitable voltage testing instrument before commencing any cable or connection work. Never rely solely on a switch being in the off position — always independently verify that the circuit is de-energised.
Bathrooms contain defined electrical zones (Zone 0, 1, 2) with specific requirements for equipment IP ratings and permitted switch types. Installing incorrect equipment in the wrong zone is dangerous and may not comply with building regulations. Verify zone classification before specifying any component.
The bathroom circuit must be protected by a 30 mA RCD or RCBO. This is mandatory in many countries and is best practice everywhere. RCD protection provides critical protection against electric shock in the wet environment of a bathroom.
All metallic parts in the bathroom — including pipework, radiators, and any metallic fan housing — must be connected to the equipotential bonding system. This prevents dangerous voltage differences between simultaneously touchable metal parts in the event of a wiring fault.

Tools needed

Voltage tester or proving unit (to verify dead before work)
Non-contact voltage tester
Insulated screwdrivers (flat and Pozidriv/Phillips)
Cable stripper and wire stripper
Continuity and insulation resistance tester (for testing on completion)
RCD tester (for verifying RCD trip time and current)
Drill with appropriate bits (for ceiling penetration and fixings)
Fish tape or cable pulling tools (for routing cable in voids)
Spirit level

Common mistakes

Using a standard single-pole switch inside the bathroom zones instead of a double-pole pull-cord isolator — single-pole switches disconnect only the live conductor and are not permitted within bathroom zones under most wiring regulations.
Fitting a fan timer or controller rated only for resistive loads — fan motors are inductive loads. A timer not rated for inductive loads may arc, fail prematurely, or cause interference. Always use a timer explicitly rated for motor loads.
Omitting RCD protection on the bathroom circuit — 30 mA RCD protection is mandatory in most jurisdictions and is a critical safety measure in wet areas. A circuit without RCD protection does not comply with modern wiring standards.
Not sleeving the bare earth conductor with green-and-yellow insulation at connection points — exposed bare earth conductors in a live enclosure can cause confusion during future maintenance and may not comply with wiring regulations.
Connecting the fan to the unswitched permanent live rather than the switched live — the fan then runs continuously whenever the MCB is on, with no user control. Always connect the fan to the appropriate switched live (the same switched live as the light, or a separate switched live if independently controlled).

Troubleshooting

Fan runs but does not stop after the light is turned off: Cause: Timer overrun period is set too long, or the timer is wired incorrectly — specifically, the timer control input may be connected to a permanent live rather than a switched live, so it never receives the off signal to start timing Fix: Verify the timer wiring against the manufacturer's connection diagram. The timer's switched live input must receive voltage from the light switch output (not from a permanent live). Adjust the overrun timer setting if the wiring is correct but the run-on period is excessive.
Fan hums but the impeller does not spin: Cause: Seized fan motor bearings or blocked impeller — common in fans that have operated for years in a humid environment causing bearing corrosion, or when lint and dust accumulate on the impeller blades Fix: Isolate power at the consumer unit. Remove the fan cover and manually check whether the impeller spins freely. Clean impeller blades of accumulated debris. If the motor bearings are seized, the fan unit requires replacement — motor-only replacements are not typically available for low-cost combined units.
MCB trips immediately when the fan circuit is switched on: Cause: Short circuit in the fan wiring, fan motor windings shorted to earth (ground fault), or a wiring error creating a live-to-neutral or live-to-earth short Fix: Disconnect the fan unit from the wiring at the ceiling rose or terminal block. If the MCB holds with the fan disconnected, the fault is in the fan unit itself — replace it. If the MCB still trips with the fan disconnected, an insulation fault exists in the circuit wiring — perform an insulation resistance test to locate the fault.

Frequently asked questions

Does a bathroom extractor fan need its own circuit?

Not always — in many installations the fan is spurred off the existing lighting circuit via a fused connection unit (FCU) rated at 3 A or 5 A. However, a dedicated radial circuit from the consumer unit is best practice for larger units or heated fan/light combinations. Local electrical regulations and the unit's rated power determine the correct approach — consult a licensed electrician.

Can I use a standard wall switch in a bathroom to control the fan?

It depends on the zone. Under IEC 60364-7-701 (and equivalents such as BS 7671 Part 7), standard switches are not permitted in Zone 0 or Zone 1. In Zone 2, switches with at least IPX4 ingress protection may be acceptable. Outside the bathroom zones entirely, a standard switch is permitted. A ceiling-mounted double-pole pull-cord isolator is the common solution within the room.

What is an overrun timer and why is it used with bathroom fans?

An overrun timer keeps the exhaust fan running for a set period — typically 5 to 30 minutes — after the light switch or fan switch is turned off. This ensures moisture-laden air is fully cleared from the room after use. Some building regulations require an overrun function; even where not mandatory, it significantly reduces condensation and mould growth on bathroom surfaces and ceilings.

Why does a bathroom fan need to be earthed if it is plastic?

The earth conductor in the circuit provides a low-impedance fault path that ensures any live-to-earth fault will blow the MCB or fuse quickly, disconnecting supply before the fault current can injure a person. Even with a plastic-bodied fan, an internal wiring fault could make internal metal parts live. Earth continuity also ensures RCD operation if one is fitted, which is strongly recommended for bathroom circuits.

Can I wire the bathroom fan to come on automatically with the light?

Yes — this is the most common bathroom fan wiring arrangement. The fan is wired to a switched live that is the same feed as the light, so both energise simultaneously. An overrun timer in series with the fan adds the post-light-off run-on period. Humidity sensor fans take a permanent live and switch themselves on when relative humidity exceeds a set threshold.

How do I wire a bathroom fan and light together on one diagram?

When wiring a bathroom fan and light together, both the fan and the light fitting share the same switched live from the bathroom switch, so the supply enters the switch, and separate switched lives run out to the fan and to the light. If a time-delay overrun fan is used, the switched live feeds a built-in timer module in the fan unit, which keeps the fan motor running for a set period (typically 5–15 minutes) after the switch is opened. Earth conductors must be connected to all metal enclosures, and the circuit should be protected by a residual current device (RCD/GFCI) as required by local wiring regulations.