Bathroom Electrical Zones London — BS 7671 Zone 0, 1, 2 Made Simple

BS 7671 Section 701 defines 'locations containing a bath or shower' as a special location requiring specific electrical safety measures. The reasoning is practical: water increases the conductivity of human skin, dramatically reducing the threshold at which an electric shock causes harm.

Section 701 splits the bathroom into three zones — Zone 0, Zone 1, and Zone 2 — each defined by physical proximity to the water source (bath or shower). Each zone has its own minimum IP (ingress protection) rating and restrictions on what equipment can be installed.

RCD protection is mandatory on all circuits serving bathroom equipment, including socket-outlets, lighting, electric showers, and bonding to extraneous-conductive-parts where required. The relevant RCD is 30 mA additional protection under regulation 415.1.

BS 7671:2018 + Amendment 4 (April 2026) refined the zone definitions and clarified the supplementary bonding rules in pre-amendment installations. The substantive zones themselves have remained stable since the 17th Edition.

Zone 0 is the interior of the bath itself or the shower tray. Anything mounted inside the bath or inside the shower enclosure below shower-head spray height is Zone 0.

Equipment in Zone 0 must be IPX7 minimum (protected against temporary immersion in water to 1m depth for 30 minutes) and must be SELV (Separated Extra-Low Voltage) at no more than 12V AC RMS or 30V DC.

In practice, Zone 0 equipment is limited to 12V SELV underwater lighting (rare in residential), 12V SELV underwater speakers (also rare), and specific 12V whirlpool bath pumps that the manufacturer has certified for Zone 0 use.

Standard 230V mains equipment in Zone 0 is never compliant. An EICR finding a 230V socket or appliance in Zone 0 is a C1 (danger present) — the immediate fix is disconnection.

Zone 1 is the volume directly above Zone 0, extending up to 2.25m above floor level (or above the underside of the bath where higher than floor level). It includes the entire space directly above the bath or shower tray.

Equipment in Zone 1 must be IPX4 minimum (protected against splashing water from any direction). 230V equipment is permitted in Zone 1 provided it is rated IPX4 and is supplied via a 30 mA RCD.

Common Zone 1 installations: ceiling-mounted LED downlights directly above the bath (IPX4-rated, RCD-protected), wall-mounted shower spotlights, electric shower controls, fixed water heaters. All require IPX4 minimum and 30 mA RCD protection.

Switches in Zone 1 are not permitted, with the specific exception of pull-cord switches mounted at or above 2.25m where the cord control allows operation without the user being in Zone 0 or 1. Standard rocker switches in Zone 1 are non-compliant.

Zone 2 is the volume extending 0.6m horizontally from the outer edge of Zone 1, at the same height (up to 2.25m). For a typical bath against a wall, Zone 2 extends 0.6m beyond the open side of the bath.

Equipment in Zone 2 must be IPX4 minimum (the same as Zone 1) and supplied via a 30 mA RCD. 230V equipment is permitted with these conditions.

Common Zone 2 installations: shaver sockets (BS EN 61558-2-5 isolating transformer type — these are specifically permitted in Zone 2), bathroom extractor fans, basin-side LED lights, and floor-standing storage heater controls.

Switches in Zone 2 are permitted only if they are isolating-transformer shaver sockets, low-voltage switches at SELV potential, or pull-cord switches at 2.25m or above. Standard 230V rocker switches in Zone 2 are non-compliant.

Zone 2 ends where the 0.6m horizontal projection from Zone 1 ends. Equipment beyond Zone 2 is outside the special-location requirements and only needs to satisfy the standard BS 7671 sockets-and-lighting regulations — though 30 mA RCD protection applies to all bathroom-circuit equipment regardless of zone.

Supplementary bonding connects the exposed metal parts in the bathroom — bath tap, pipework, radiator, towel rail — to the circuit protective conductor, ensuring that any fault current is diverted to earth rather than passing through a person in contact with two metal surfaces.

Pre-17th Edition installations always required supplementary bonding in bathrooms. A bathroom inspected during an EICR that lacks visible supplementary bonding can still be compliant under 18th Edition rules.

The 18th Edition (2018) — section 701.415.2 — allows supplementary bonding to be omitted where ALL of the following are satisfied: every circuit in the bathroom has 30 mA RCD additional protection; all extraneous-conductive-parts are connected to the main protective bonding at the consumer unit; the installation meets the disconnection times required by chapter 41.

Practical reading: a modern London bathroom served by RCD-protected circuits from a fully bonded consumer unit does not need supplementary bonding in the bathroom itself. An older bathroom on non-RCD circuits or with incomplete main bonding still needs the supplementary bonding in place — pulling it out without first installing RCD protection downgrades the installation.

Common EICR scenario: a 1990s installation with main bonding but no RCDs and no supplementary bonding. This is a C2 (potentially dangerous) — the path is either to add 30 mA RCD protection at the consumer unit (preferred, also future-proofs the install), or to retrofit supplementary bonding in the bathroom.

C1 — 230V socket-outlet in Zone 0, 1 or 2 (other than a shaver isolating transformer). Immediate disconnection required.

C1 — Light fitting without IPX4 rating mounted in Zone 1 (e.g. standard ceiling rose with paper or fabric shade above a bath). Replace with appropriate IPX4 fitting before re-energising.

C2 — Non-RCD-protected circuit serving bathroom lighting or shower. Add 30 mA RCD protection at the consumer unit or replace the circuit's MCB with an RCBO.

C2 — Missing main protective bonding to extraneous-conductive-parts (gas, water, central heating) in a property where supplementary bonding has been omitted on the basis of 18th Edition rules. The bonding hierarchy is then incomplete and the installation is non-compliant.

C2 — Switch (other than a permitted pull-cord at 2.25m) in Zone 1 or Zone 2. Replace with a wall switch outside the zone or a compliant pull-cord switch.

C3 — Type AC RCD where the circuit serves equipment likely to produce DC fault current (LED drivers, electronic shower controls). Type A RCD is recommended; A4 to BS 7671 from April 2026 expects Type A for new work but does not retrospectively code Type AC as a C2.

C3 — Old-style rotary switch outside Zone 2 but visible in the bathroom. Functional but cosmetically dated; improvement recommended.

Bathroom downlights placed mid-zone without verification. A common 'feature lighting' installation places 3–5 downlights in a row above the bath; the row often crosses Zone 1 and Zone 2 with fittings not all rated IPX4. Easy C2 finding on an EICR — replace non-compliant fittings with IPX4 LED downlights.

Bathroom shaver sockets repurposed as USB charging points. A shaver socket is specifically a BS EN 61558-2-5 isolating transformer outlet. Some installs add USB charging adapters into the shaver socket — fine if the adapter is the shaver-socket-specific type, non-compliant if it is a generic USB unit drawing 230V.

Towel rail wired without supplementary bonding in pre-18th Edition installation. A common refurbishment install adds an electric towel rail to the existing bonding scheme. If the property's bathroom previously had supplementary bonding, the new towel rail should be included; if the original installation omitted it on 18th Edition grounds, the towel rail's circuit needs RCD protection at the consumer unit.

Mirror demister pads in Zone 1 wired into the lighting circuit without dedicated RCD. Demister pads are 230V resistive heaters; they need IPX4 enclosure (usually integral to the mirror), 30 mA RCD protection, and an isolation switch outside Zone 2.

Underfloor heating mats in en-suites without manufacturer-rated bathroom compatibility. Standard UFH mats are not rated for Zone 0/1/2 use; bathroom-specific mats are required. EICR finding: C2 where the mat is not bathroom-rated.

Practical inspection: a bathroom is a special location and the EICR engineer should explicitly verify zoning, IP ratings, and RCD protection. A landlord receiving a clean EICR on a property with a recently-refurbished bathroom should check that the engineer specifically inspected the bathroom and noted the zoning compliance in the report.