Bathroom electrical regulations, explained without the jargon

Zones, in plain English

The regulations divide a bathroom into zones based on proximity to the bath or shower. Zone 0 is inside the bath or shower tray itself. Zone 1 is directly above it, up to 2.25 metres. Zone 2 extends 0.6 metres beyond zone 1 and also covers the area around a washbasin tap. Everything else is outside the zones, though it is still a bathroom and still damp.

Each zone has a minimum enclosure protection rating. Anything in zone 0 has to be rated for immersion and run at very low voltage. Zone 1 fittings must be protected against water jets or sprays as a minimum, and zone 2 fittings against splashing. Downlights above a shower are the everyday example: they need an appropriate IP rating, not just a nice bezel.

• Zone 0: inside the bath or shower tray, very low voltage only
• Zone 1: above the bath or shower to 2.25m, protected enclosure required
• Zone 2: 0.6m beyond zone 1 and around basin taps
• Outside zones: normal fittings, but damp resistance is still sensible

Why there are no ordinary sockets

Standard 13A socket outlets are not permitted within three metres of the boundary of zone 1. In an average UK bathroom that rules the whole room out, which is why bathrooms have shaver supply units instead. A shaver unit contains an isolating transformer, so the output is not referenced to earth and cannot deliver a shock through you to the pipework.

This is also why people quietly run an extension lead in from the landing for a heater or a hair dryer, and why that is genuinely dangerous rather than merely against the rules. The restriction exists because a shock in a wet room with earthed metalwork is far more likely to be fatal than the same shock in a bedroom.

Showers, fans and heated towel rails

An electric shower needs its own dedicated circuit sized to the unit, protected appropriately, with an isolator that is accessible but positioned outside the zones or operated by a pull cord. Upgrading from an 8.5kW to a 10.5kW shower is not a like for like swap: the cable and protective device have to suit the new rating, and sometimes the existing cable will not.

Extractor fans in a shower zone need the right rating and, where fitted with a timer, a supply that keeps the overrun working after the light goes off. Heated towel rails are usually fitted as fixed appliances with a fused connection unit sited outside the zones, not plugged in.

• Electric showers need a dedicated correctly sized circuit and isolator
• Fans need the correct IP rating for their zone and a properly wired overrun
• Towel rails should be fixed connections, not plug and socket
• Any bathroom circuit needs RCD protection

Supplementary bonding and when it can be omitted

Older bathrooms often have green and yellow bonding conductors linking pipework, the bath and any metal parts. Under current standards that supplementary bonding can be omitted where all circuits serving the room have RCD protection, the main protective bonding is present and correctly sized, and disconnection times are met.

In practice, that is the whole test. If the main bonding to the incoming gas and water is undersized or missing, or the circuits are not all RCD protected, the supplementary bonding has to stay or be added. That is one of the most common reasons a bathroom refit turns into a wider piece of work, and it is why the survey looks at the consumer unit and the bonding rather than just the room.

Refit sequencing and certification

Bathroom electrical work follows the same first fix and second fix pattern as a kitchen: cables in before plastering and tiling, accessories and fittings after. Deciding on the shower, mirror and fan before first fix matters even more here, because chasing a tiled wall afterwards means retiling.

New circuits in a bathroom are notifiable under Part P. A registered electrician certifies and notifies the work, and you receive the certificate. Keep it with the property paperwork.