Everything you need to know about bathroom electrical installations under BS 7671. Zone definitions, IP ratings, supplementary bonding under Regulation 701.415.2, RCD protection, SELV, switching, socket outlets, and electric shower circuits.
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Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.
BS 7671 Section 701 divides a room with a bath or shower into Zone 0 (inside the bath/basin), Zone 1 (above it to 2.25 m) and Zone 2 (0.6 m beyond Zone 1). Equipment must meet a minimum IP rating for its zone — IPX7 in Zone 0, IPX4 in Zones 1 and 2 (IPX5 where water jets are used) per Reg 701.512.2. All circuits serving the location need 30 mA RCD additional protection (Reg 701.411.3.3), and supplementary equipotential bonding (Reg 701.415.2) is required unless the conditions for omitting it are met. Socket-outlets are prohibited within 2.5 m horizontally of the Zone 1 boundary (shaver units to BS EN 61558-2-5 and SELV sockets excepted) per Reg 701.512.3.
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Section 701 of BS 7671:2018+A4:2026 covers the particular requirements for locations containing a bath or shower. It is one of the most frequently examined and most commonly encountered special locations in domestic electrical work.
The underlying principle is straightforward: a person in contact with water has significantly reduced body resistance, making them more vulnerable to electric shock. BS 7671 addresses this by defining zones of increasing risk around baths and showers, then restricting what equipment and wiring may be installed in each zone.
Section 701 applies to the electrical installation in locations containing a fixed bath or shower and to the surrounding zones. Per Regulation 701.1, it does not apply to emergency facilities such as emergency showers used in industrial areas or laboratories.
This guide covers zone definitions, IP rating requirements, supplementary bonding under Regulation 701.415.2, RCD protection, SELV, switching devices, socket outlets, and electric shower circuits.
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BS 7671 defines the zones in a bathroom or shower room. The zones are measured from the bath, shower basin, or (for showers without a basin) the fixed water outlet. Zone dimensions are illustrated in Figures 701.1 (plan) and 701.2 (elevation) of BS 7671.
IP minimums per Reg 701.512.2; 30mA RCD additional protection per Reg 701.411.3.3; Zone 0/switch SELV limits per Reg 701.512.3; Zone 1 SELV/PELV equipment limit per Reg 701.55.
The interior of the bath or shower tray. For showers without a tray, Zone 0 is the area of the floor up to 0.1m above the floor level, within the horizontal extent of Zone 1. Only SELV at a maximum of 12V AC rms or 30V ripple-free DC is permitted. The safety source must be outside Zones 0, 1, and 2. Equipment must be rated at least IPX7.
Above the bath or shower basin, bounded by the finished floor and the higher of 2.25m or the highest fixed shower head. Horizontally it extends to the plane circumscribing the basin, or 1.2m from the centre of the fixed water outlet for showers without a basin (in which case there is no Zone 2). Equipment must be at least IPX4 and only fixed, permanently connected current-using equipment suitable for the zone is permitted. SELV up to 25V AC rms or 60V ripple-free DC is allowed with the source outside Zones 0, 1, and 2.
Extends 0.6m horizontally beyond Zone 1, from the finished floor level up to 2.25m. Equipment must be rated at least IPX4. Fixed current-using equipment, luminaires, and shaver supply units (BS EN 61558-2-5) are permitted. Switches are only permitted if they form part of fixed current-using equipment suitable for the zone.
Beyond the zones and above the Zone 1/2 height. Normal installation rules apply, subject to the requirement that all circuits serving the location have 30mA RCD additional protection. Socket outlets may be installed here provided they are more than 2.5m horizontally from the boundary of Zone 1. Switchgear, accessories, and general equipment are permitted.
The ceiling above a bath is classified as outside the zones provided it is above the Zone 1 height (the higher of 2.25m or the highest fixed shower head). A luminaire on a ceiling higher than that boundary is outside the zones — but the same fitting falls within Zone 1 or 2 if the ceiling is lower, and must then meet the IPX4 minimum. See our IP rating guide for decoding the IP code when selecting bathroom fittings.
IP (Ingress Protection) ratings define the degree of protection equipment provides against solid objects and water. In bathroom zones, the minimum IP rating requirements are:
The second digit of an IP code describes protection against water. The relevant codes for bathroom work decode as follows:
IP codes are defined in BS EN 60529; an “X” means the solid-object digit is not specified.
The IP rating must be maintained after installation — this means cable entries, mounting screws, and enclosure seals must all be intact. A luminaire rated IPX4 at the factory loses its rating if the installer drills an unsealed cable entry. The suitability of equipment for its location in terms of IP rating is itself an item inspectors verify under Regulation 701.512.2.
Supplementary equipotential bonding in bathrooms has been one of the most debated topics in the 18th Edition. Regulation 701.415.2 allows supplementary bonding to be omitted if specific conditions are met.
If supplementary bonding is required (because the above conditions are not met), it must connect together the terminals of the protective conductors of each circuit supplying the location and all extraneous-conductive-parts within the location. This includes metal pipework (hot, cold, gas, central heating), metal baths, metal waste pipes, structural steelwork, and any other metallic part that could introduce a potential.
The minimum cross-sectional area depends on what the conductor connects (Section 544). A supplementary bonding conductor between two extraneous-conductive-parts must be at least 2.5mm² where sheathed or mechanically protected, or 4mm² where not (Regulation 544.2.3). A conductor connecting an exposed-conductive-part to an extraneous-conductive-part must be at least half the cross-sectional area of the relevant circuit protective conductor, again subject to a 4mm² minimum where mechanical protection is absent (Regulation 544.2.2). Always verify the main bonding and earth fault loop impedance before deciding to omit supplementary bonding.
Regulation 701.411.3.3 requires that all circuits serving the bathroom location are protected by an RCD with a rated residual operating current (IΔn) not exceeding 30mA. This applies to every circuit type — lighting, power, shower, heated towel rail, underfloor heating, extractor fan, and any other circuit serving the bathroom.
In a modern dual-RCD or RCBO consumer unit, most circuits are already 30mA RCD-protected. On older installations with a main switch only, upgrading the consumer unit may be the most practical way to achieve compliance.
SELV (Separated Extra-Low Voltage) is a protective measure permitted in all bathroom zones and is the only electrical supply permitted in Zone 0. The requirements are:
SELV circuits must have protective separation from all other circuits, achieved through a safety isolating transformer conforming to BS EN 61558-2-6 or equivalent source of safety supply. Live parts of SELV circuits in Zones 0 and 1 must not be accessible — even at extra-low voltage.
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Regulation 701.512.3 restricts the installation of switchgear and accessories in bathroom zones:
Ceiling-mounted pull-cord switches are the standard solution for bathroom lighting in domestic properties. The switch mechanism is at ceiling level (outside the zones) and the cord is an insulating medium.
Socket outlets are not permitted in Zones 0, 1, or 2. Regulation 701.512.3 further prohibits socket-outlets within a distance of 2.5m measured horizontally from the boundary of Zone 1. A socket-outlet may therefore only be installed beyond that 2.5m line, and must have 30mA RCD additional protection.
In most domestic bathrooms, this 2.5m clearance cannot be achieved, so socket outlets are not installed. The exceptions permitted in Zone 2 or outside the zones are:
Large hotel bathrooms and en-suites in large houses may have sufficient distance from Zone 1 to accommodate a socket outlet. Always measure carefully and document the measurement on the certificate.
Electric showers are one of the highest-demand fixed appliances in a domestic installation. At 230V, the design current is simply the rated power divided by the voltage, so a typical 8.5–11kW shower draws roughly 37–48A. The circuit must comply with both the general requirements of BS 7671 and the specific requirements of Section 701.
Indicative only. The protective device and cable size must be calculated for the actual installation method, length and grouping, and verified against the manufacturer’s instructions and BS 7671 Appendix 4 current-carrying capacities.
Use Elec-Mate's cable sizing calculator to determine the correct cable size for electric shower circuits, accounting for installation method, grouping…
Try it free for 7 daysBathroom installations require the same testing as any other circuit, plus particular attention to:
An EIC or Minor Works Certificate must be issued. On EICRs, common observations include missing supplementary bonding (where required), incorrect IP ratings, socket outlets within zones, and absent or non-functional RCD protection.
Bathroom electrical work is Part P notifiable (unless a like-for-like replacement of accessories on the same circuit). Every new circuit, new shower installation, or consumer unit change affecting bathroom circuits requires either self-certification through a competent person scheme or Building Control notification.
Common pitfalls on bathroom installations include:
Drilling cable entries into IPX4 fittings without resealing. Using non-rated connectors inside zone-rated enclosures. Always use manufacturer-supplied grommets and seals.
Measuring zones from the wrong reference point. For a bath, Zone 1 is measured from the outer edge of the bath rim. For a shower without a tray, it is 1.2m from the fixed water outlet.
Elec-Mate's digital certificates include bathroom-specific fields and zone diagrams. Complete your EIC or Minor Works on your phone immediately after…
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