Bathrooms are one of the highest-risk environments for electrical installations. BS 7671 Part 7 Section 701 sets out specific requirements for bathroom zones, IP ratings, RCD protection, supplementary bonding, and SELV circuits. This guide explains every requirement in practical terms.
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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.
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Bathrooms present a unique set of electrical hazards. The combination of water, steam, wet skin (which has significantly lower resistance than dry skin), bare feet on conductive surfaces, and earthed metallic pipes and fittings creates conditions where even a small fault current can cause a fatal electric shock. BS 7671 Part 7 Section 701 addresses these hazards by imposing strict requirements on what electrical equipment can be installed, where it can be placed, and how it must be protected.
The regulations apply to any room containing a bath or shower — this includes en-suite bathrooms, wet rooms, shower rooms, and any other room where a bath or shower is installed. They also apply to shower cubicles in bedrooms (increasingly common in hotel-style conversions) and to swimming pool shower areas. The key principle is that the closer electrical equipment is to the water source, the higher the protection requirements.
For electricians, bathroom work is some of the most regulation-intensive domestic electrical work. An EICR inspection of a property always requires careful assessment of the bathroom installation, and new bathroom circuits require detailed design consideration.
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BS 7671 divides the bathroom into distinct zones based on the proximity to the bath or shower. Each zone has specific requirements for the type of equipment that can be installed and the minimum IP (Ingress Protection) rating required.
Zone 0 is the interior of the bath or shower tray — the space that can contain water. Only fixed equipment specifically designed for use in this zone is permitted. The equipment must be rated at least IPX7 (protected against temporary immersion) and must operate at SELV (Safety Extra-Low Voltage) not exceeding 12V AC or 30V ripple-free DC. The SELV source (transformer) must be located outside Zones 0, 1, and 2. In practice, very few items are installed in Zone 0 — underwater lighting in whirlpool baths is the most common example.
Zone 1 extends from the finished floor level (or the top of the bath rim/shower tray) up to a height of 2.25 metres above the floor, directly above the bath or shower tray. Equipment in this zone must be rated at least IPX4 (protected against splashing water from all directions). Only fixed equipment suitable for the conditions is permitted — this includes electric showers (which are specifically designed for Zone 1), instantaneous water heaters, and whirlpool units. Switches are not permitted in Zone 1 except as integral parts of fixed equipment; where SELV switches are installed in Zone 1, the circuit voltage must not exceed 12V AC RMS or 30V ripple-free DC (Reg 701.512.3). Current-using equipment (e.g. luminaires, heaters) protected by SELV or PELV is permitted at up to 25V AC RMS or 60V ripple-free DC (Reg 701.55), with the safety source located outside Zones 0, 1, and 2.
Zone 2 extends 0.6 metres horizontally beyond Zone 1 and up to 2.25 metres above the floor. It also includes the area above Zone 1 between 2.25m and 3.0m above the floor, directly above the bath or shower. Equipment in Zone 2 must be rated at least IPX4 (IPX5 where water jets are used for cleaning purposes). Luminaires, fans, heaters, and shaver sockets to BS EN 61558-2-5 (with an isolating transformer) are permitted in Zone 2, provided they have the required IP rating.
The area outside the defined zones is subject to the general requirements of BS 7671 rather than the specific bathroom zone requirements. Standard switches, socket outlets, and equipment can be installed here, subject to the general regulations. However, 30mA RCD protection is still mandatory for all circuits in the bathroom, including those serving equipment outside the zones. Socket outlets (other than shaver sockets) are permitted outside the zones, provided they are at least 2.5 metres horizontally from the boundary of Zone 1 (Reg 701.418.2). Exceptions include SELV socket-outlets and shaver units complying with BS EN 61558-2-5.
For shower cubicles without a tray (walk-in showers and wet rooms), Zone 1 extends to 1.2 metres from the shower head fixing point measured horizontally. The zone dimensions are the same regardless of whether there is a physical enclosure — a shower curtain does not define the zone boundary.
The Ingress Protection (IP) rating system classifies the degree of protection provided by electrical enclosures against the entry of solid objects and water. In bathroom installations, the water protection rating (the second digit) is the critical factor.
Inside the bath/shower basin
Above bath/shower to 2.25m
0.6m beyond Zone 1
Beyond Zone 2
IPX4 means the equipment is protected against splashing water from all directions. IPX7 means the equipment is protected against temporary immersion in water (up to 1 metre depth for 30 minutes). Where water jets are used for cleaning (such as in commercial or communal bathrooms), IPX5 (protected against water jets from all directions) is required in Zones 1 and 2.
Elec-Mate's EICR form includes fields for recording the IP ratings of equipment installed in each bathroom zone, ensuring nothing is missed during inspection.
Supplementary bonding in bathrooms has been one of the most debated topics in UK electrical work since the introduction of the 17th Edition (BS 7671:2008). The position has evolved through successive editions and amendments, and the current requirements under the 18th Edition are as follows.
The rule since the 17th Edition (Reg 701.415.2): Supplementary bonding in a bathroom is not required provided that all of the following conditions are met:
If all three conditions are met, supplementary bonding is not required. If any condition is not met — for example, if there is a circuit without RCD protection, if the main bonding is inadequate or absent, or if there are extraneous conductive parts not connected to the bonding system — then supplementary bonding must be installed.
During an EICR, if supplementary bonding is absent in a bathroom, you must verify all three conditions before concluding that it is not required. If you cannot confirm all three conditions (for example, if you cannot verify the main bonding or if a circuit lacks RCD protection), the absence of supplementary bonding should be recorded as an observation or deficiency.
BS 7671 Regulation 701.411.3.3 requires that all circuits in a bathroom location must be protected by a 30mA RCD. This requirement is absolute — there are no exceptions based on the zone, the type of equipment, or the circuit rating. It applies to:
BS 7671:2018+A4:2026 introduces Reg 411.3.4, which requires additional protection by a 30mA RCD for all AC final circuits supplying luminaires in domestic premises. This reinforces and extends the bathroom-specific requirement of Reg 701.411.3.3 — bathroom lighting circuits must comply with both regulations. For EICRs on domestic properties, an unprotected lighting circuit feeding bathroom luminaires is now a non-compliance under both Part 4 and Part 7.
The RCD can be provided by an RCBO protecting the individual circuit, or by an RCD protecting a group of circuits (as in a split-load consumer unit). In either case, the rated residual operating current must not exceed 30mA and the device must be Type AC minimum (Type A is preferred for circuits with electronic equipment).
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SELV (Safety Extra-Low Voltage) is used in bathrooms to reduce the risk of electric shock in the most hazardous zones. SELV operates at voltages that are considered non-lethal — 12V AC or 30V ripple-free DC maximum in Zone 0, and 25V AC or 60V ripple-free DC in Zone 1.
The key feature of a SELV system is that the low-voltage supply is derived from a safety isolating transformer that provides galvanic separation between the mains supply and the SELV circuit. The SELV transformer must be located outside Zones 0, 1, and 2 — typically in the ceiling void above the bathroom or in an adjacent room. The SELV circuit must not be earthed (if it were earthed, it would become PELV rather than SELV, and the safety benefit would be reduced).
Common applications of SELV in bathrooms include LED downlights (12V LED drivers located outside the zones, with low-voltage cabling to the luminaires in Zone 1), shaver lights with integral SELV transformers in Zone 2, and underwater lighting in whirlpool baths (12V SELV in Zone 0).
It is important to distinguish between SELV and simple low-voltage supplies. A USB charger integrated into a shaver socket, for example, provides 5V DC — but unless the supply is via a safety isolating transformer with the required separations, it is not SELV and must not be installed in Zones 0 or 1.
Understanding what equipment can be installed in each zone is essential for both new installations and EICR inspections. The following is a practical summary of the most common bathroom equipment and where it is permitted.
Permitted in Zone 2 and outside zones. Not permitted in Zone 0 or Zone 1. Must incorporate an isolating transformer. Standard 13A socket outlets are not permitted in any zone and should be at least 3m from the boundary of Zone 1.
Permitted in Zone 1 — electric showers are specifically designed for installation in this zone. The unit must be IPX4 rated. The pull-cord switch (if separate from the unit) must be outside Zone 1 — typically on the ceiling or on a wall outside the zones. The supply cable enters the shower unit and does not pass through Zone 0.
Permitted in Zone 1 (if rated IPX4 or higher) and Zone 2 (if rated IPX4 or higher). Many bathroom extractor fans are designed for Zone 1 installation. The fan switch must be outside Zone 1 — a pull-cord on the ceiling is a common solution, or a wall switch outside the zones.
Permitted in Zone 1 (if rated IPX4 and suitable for the zone), Zone 2 (if rated IPX4), and outside zones (general IP rating). IP-rated LED downlights are the most common Zone 1 lighting solution. The light switch must be outside Zone 1 — a pull-cord or a switch outside the bathroom door.
If electric, permitted in Zone 2 and outside zones with appropriate IP rating. Not permitted in Zone 0 or Zone 1 unless specifically designed and rated for the zone. Most electric towel rails are installed outside Zone 2 or at the edge of Zone 2. The connection should be via a fused connection unit located outside the zones.
Elec-Mate's EICR and EIC certificate forms include bathroom-specific fields — zone identification, IP ratings, supplementary bonding status…
Try it free for 7 daysElectric showers are one of the most demanding domestic circuits, drawing significant power from the supply. The most common ratings are:
Entry-level shower. Requires a 40A circuit with 6mm² cable for short runs (up to approximately 18m) or 10mm² for longer runs. Adequate flow rate for most users.
Most popular domestic shower. Requires a 45A circuit with 10mm² cable. Good flow rate and temperature for year-round use. The most commonly specified size.
High-output shower. Requires a 50A circuit with 10mm² cable (short runs) or 16mm² for longer runs. Best flow rate and temperature performance but demands a robust supply.
Every electric shower circuit must have a dedicated circuit from the consumer unit — it must not share a circuit with any other equipment. The circuit must be protected by a 30mA RCD (as required for all bathroom circuits) and an appropriately rated overcurrent protective device. A double-pole isolator switch must be provided, typically a 45A or 50A ceiling-mounted pull-cord switch. The switch must be accessible to the user and located outside Zone 1.
Cable sizing is critical — voltage drop must be calculated for the specific cable length and installation method. A 10.5 kW shower on a long cable run can easily exceed the 5% voltage drop limit if the cable is undersized. Use the cable sizing calculator to verify.
Electric underfloor heating (UFH) is increasingly popular in bathrooms, providing comfortable warmth underfoot on cold tiles. From a regulations perspective, electric UFH in bathrooms requires careful consideration.
The heating element (cable mat or loose cable) is installed beneath the floor finish, typically embedded in tile adhesive or a self-levelling compound. The element is connected to a thermostat/controller, which may be located in or outside the bathroom. The entire system must be protected by a 30mA RCD (as required for all bathroom circuits).
BS 7671 Regulation 701.753 requires that electric heating systems embedded in the floor of a bathroom must have either a metallic grid connected to the protective conductor of the heating circuit (to provide earth fault detection) or be covered by the overall RCD protection of the bathroom circuits. Most modern UFH systems designed for bathrooms include a metallic earth screen within the heating mat that serves this purpose.
The thermostat should include a floor sensor (embedded in the screed alongside the heating element) to prevent overheating. The thermostat location must comply with the zone requirements — if in the bathroom, it must be outside Zone 2 and have an appropriate IP rating. Many installers locate the thermostat just outside the bathroom door for convenience and compliance.
An insulation resistance test of the heating element should be carried out before and after installation of the floor finish, to identify any damage to the element during the tiling process. The results should be recorded on the Electrical Installation Certificate.
A step-by-step guide to inspecting the electrical installation in a bathroom during an EICR or when certifying new work.
Measure and identify Zone 0 (inside the bath/shower), Zone 1 (above the bath/shower to 2.25m from floor level), Zone 2 (0.6m beyond Zone 1 horizontally and the area between 2.25m and 3.0m above the bath/shower), and the area outside zones. For walk-in showers without trays, Zone 1 extends 1.2m from the shower head fixing point. Record the zone layout.
Verify that every piece of electrical equipment in the bathroom has an IP rating appropriate for its zone. Zone 0 requires IPX7, Zone 1 and 2 require IPX4 minimum. Check luminaires, extractor fans, shaver sockets, shower units, and any other fixed equipment. Record the IP ratings on the EICR schedule.
Confirm that every circuit serving the bathroom is protected by a 30mA RCD. Test each RCD for correct operation — the test button and instrument test (at rated current and 5x rated current). Record the RCD type, rating, and measured operating times.
Check whether supplementary bonding is installed. If it is not, verify that all three conditions for omitting it are met: all circuits RCD-protected, main bonding satisfactory, and all extraneous conductive parts connected to the bonding system. If supplementary bonding is present, check continuity and connections.
Carry out the full testing sequence for each bathroom circuit: continuity of protective conductors, insulation resistance, polarity, earth fault loop impedance (Zs), and prospective fault current. For shower circuits, verify cable sizing against the load current and measured voltage drop.
Document all findings on the EICR or EIC, including zone identification, IP ratings, RCD test results, bonding status, and any observations or deficiencies. Use the appropriate observation codes for any non-compliances found.
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