Does an LED bathroom mirror need an FCU in the UK?

Yes. An LED illuminated mirror requires a fused connection unit (FCU) rather than a standard plug and socket. Sockets are not permitted inside a bathroom under BS 7671 (with the exception of a shaver supply unit complying with BS EN 61558-2-5). The FCU provides a fused, isolated supply to the mirror and can be sited on the wall outside Zone 2 — typically near the door — with cable running back to the mirror position.

Where must the FCU be positioned in a bathroom?

The FCU must be outside Zone 2, which means at least 0.6 metres measured horizontally from the rim of the bath or the edge of a shower enclosure. In most bathrooms this means the FCU goes on the wall beside or just outside the door. If the bathroom is large enough that 0.6 metres from the bath still leaves room on a bathroom wall, you can mount the FCU there, but keeping it outside the room entirely avoids any ambiguity about zone measurement.

What fuse size should I use in the FCU for an LED mirror?

A 3A cartridge fuse is correct for most LED bathroom mirrors, which typically draw between 15W and 40W. If the mirror includes a demister heating pad, check the total wattage on the data plate — a 40W mirror with a 60W demister totals 100W, which is still within a 3A fuse. Mirrors with larger demister pads approaching 200W or more may require a 5A fuse. Always check the mirror manufacturer's instructions, which will state the recommended fuse rating.

How to Wire an LED Illuminated Bathroom Mirror via FCU (UK)

Helpful video reference. The embedded video shows a UK bathroom LED mirror installation using a fused connection unit spur, with clear coverage of bathroom basin zones, FCU siting rules and the wiring sequence. It uses UK-specific terminology throughout, including zone measurements and FCU terminal labelling. Original video: "Installing an electric LED mirror in a bathroom fused connection unit FCU spur bathroom basin zones".

Before you start. Bathroom electrical work sits under BS 7671 Section 701 and is Part P notifiable in England and Wales if you are adding new circuits or extending beyond an existing accessory position. Running a new spur to a new FCU location is notifiable — either self-certify through a competent persons scheme or use a registered electrician. If you are replacing an existing FCU in the same position for a new mirror, notification is generally not required, but always check with your local building control if you are unsure.

1. Identify the bathroom zones and plan the FCU position

BS 7671 Section 701 divides a bathroom into zones based on proximity to the bath or shower. Zone 1 is inside the bath tub or shower tray and the space directly above it up to 2.25 metres from the floor. Zone 2 extends 0.6 metres horizontally outwards from the rim of the bath or the threshold of a shower enclosure, up to the same height.

An FCU can be installed outside Zone 2 — more than 0.6 metres from the bath edge. In most bathrooms this means the FCU goes on the wall near the door, or just outside the room on the landing. Measure carefully: the 0.6 metre distance is horizontal, not diagonal.

Sketch the layout before ordering materials. The FCU position determines cable run length and routing, which affects whether you are tapping from a ring circuit socket on the other side of the wall, or running a longer cable back to the consumer unit area. In most cases a spur from the nearest ring circuit socket or junction box is the tidiest approach.

2. Choose the right FCU and fuse rating

A standard 13A fused connection unit — switched or unswitched — in white or chrome to match your bathroom accessories is the right product. A switched FCU is more convenient as it lets you cut power to the mirror without visiting the consumer unit.

For the fuse: most LED bathroom mirrors draw under 40W for the lamp, and up to 100-150W total if there is a demister pad. At 230V, 150W is 0.65A — well within a 3A fuse. Check the data plate on your specific mirror. If the total wattage stated on the plate is above 690W (unlikely for a bathroom mirror) you would need a 5A fuse, but in practice a 3A cartridge is correct for nearly every domestic LED mirror.

If the FCU will be inside Zone 2 for any reason — which should be avoided but occasionally arises in very small bathrooms — it must be IP44 rated as a minimum. Standard surface-mounted FCUs are typically IP2X only, so choose a flush-mounted model with an appropriate faceplate if you are in any doubt about zone proximity.

3. Identify and isolate the supply circuit

The easiest supply for a bathroom mirror FCU is the ring final circuit on the other side of the bathroom wall, or the nearest ring circuit socket in an adjacent room. A ring circuit can take one unswitched spur from any socket or junction box that is itself on the ring (not already a spur).

To confirm a socket is on the ring: switch off the circuit, disconnect the socket and measure continuity between the two line conductors, then between the two neutrals. A ring has two cables entering the socket; a spur has one. Do not add a spur to an existing spur — this overloads the original connection point.

Once you have identified a suitable take-off point, switch off the circuit at the consumer unit. Confirm dead at the socket with a voltage tester and lock off the MCB before disconnecting anything.

4. Run cable from the supply to the FCU position

Use 2.5mm² twin and earth for a ring circuit spur. This is slightly more cable than the LED mirror load strictly requires, but it matches the ring circuit cable size and is the standard for spur wiring.

If the FCU is on an adjoining wall to the mirror, you may need to run cable through the wall cavity or surface-route it in trunking. In a tiled bathroom, think carefully about routing before starting — cable concealed under tiles needs to be in conduit and must follow the standard cable zones (vertical from a socket or switch, horizontal from the ceiling or floor).

A second, shorter cable of 1.0mm² twin and earth or three-core flex runs from the FCU load terminals to the mirror's supply connection, if the mirror is not supplied with its own mains lead. Keep this run as short as possible and conceal it behind the mirror body if the mirror sits proud of the wall.

5. Connect the supply side of the FCU

At the FCU back box, connect the supply cable: brown conductor to the terminal marked LINE IN (or L IN), blue to NEUTRAL IN (N IN), and the earth conductor — sleeved green-and-yellow if it is bare copper — to the earth terminal. Tighten all terminals firmly.

Fit the 3A cartridge fuse into the fuse carrier inside the FCU. The fuse carrier usually snaps or slides into place — check it is fully seated before fitting the faceplate.

Do not restore power yet. Complete the mirror-side connection first so there is no open live terminal once the circuit is restored.

6. Connect the mirror supply cable to the FCU load side

At the FCU load terminals (LINE OUT, NEUTRAL OUT, earth), connect the cable running to the mirror: brown to L OUT, blue to N OUT, earth to the earth terminal.

At the mirror end, follow the mirror manufacturer's wiring instructions. Most LED bathroom mirrors have a terminal block inside the mirror body, accessed by removing a small cover plate or sliding off the mirror face plate. Some come with a short mains lead already attached — in that case, simply connect the lead's flying conductors to the FCU load terminals in the same way.

Ensure the earth is connected at both ends if the mirror has any exposed metalwork. Mirrors with aluminium frames or chrome surrounds must be earthed, even if the electronic components inside are double-insulated.

7. Restore power and test

Check all terminals are tight and no bare copper is visible outside any terminal. Refit the FCU faceplate and the cover at the supply take-off point. Restore the circuit at the consumer unit.

Switch on the FCU and check the mirror lights up. If the mirror has a demister, allow one to two minutes for it to warm up — you should feel gentle warmth across the mirror glass when it is working. Test any touch switches, shaver sockets or Bluetooth speakers if fitted.

If the FCU fuse blows on first switch-on, do not simply fit a higher-rated fuse. Check whether the mirror has a short circuit (use a continuity tester between line and neutral with the FCU fuse removed) and confirm the mirror wattage matches your fuse rating before reinstating power.

Stop and call an electrician if: the bathroom has no existing wiring on a ring circuit accessible without major chasing; the FCU position you need is closer than 0.6 metres from the bath edge and there is no other practical option; the mirror is in Zone 1 or Zone 2 and needs a supply cable routed through that zone — cables in Zone 1 and Zone 2 must be adequately protected and routed correctly; you are unsure whether the existing ring circuit already has its full complement of spurs; or the installation is in a rented property where a landlord electrical safety check (EICR) is required and you want the work formally certified.

When to call us

New FCU wiring for a bathroom mirror is straightforward work but does require Part P notification in England and Wales when it involves a new circuit extension. Richard can fit the FCU, run the cable, connect the mirror and issue the appropriate certificate as a small local job. He covers Sandwich and east Kent and charges at the £10 per 10-minute local rate with no minimum call-out for CT13.

Need bathroom electrical work in Sandwich?

Richard handles LED mirror wiring, FCU installations and bathroom electrical inspections as small local jobs. Fully qualified and Part P registered. No minimum call-out in CT13.

Contact Richard

How to wire an LED illuminated bathroom mirror