4.2 Special Locations & Bathroom Zoning Requirements

4.2 Special Locations & Bathroom Zoning Requirements

Part 7 of BS 7671 specifies safety rules for Special Locations—environments where the risk of electric shock is significantly heightened due to environmental factors such as moisture, water immersion, or low body resistance. Section 701 governs installations in locations containing a bath tub or shower basin.

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The Physics of Wet Environments & Electric Shock Risk

Under dry conditions, human skin provides a nominal electrical resistance ranging from $10,000\text{ }\Omega$ to over $100,000\text{ }\Omega$. However, when skin is saturated with water or perspiration, skin resistance drops to approximately $500\text{ }\Omega$ to $1000\text{ }\Omega$.

Consequently, a standard $230\text{ V}$ shock in a wet environment forces a body current ($I = V/R$) exceeding $230\text{ mA}$ through the heart—far higher than the $30\text{ mA}$ threshold that triggers ventricular fibrillation. To mitigate this hazard, BS 7671 establishes strict dimensional zoning, voltage restrictions, and ingress protection requirements.

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Classification of Bathroom Zones (BS 7671 Section 701)

Locations containing a fixed bath tub or shower are divided into three distinct zones based on distance from the water source:

  │◄───────────────────────────── 2.25 m ─────────────────────────────►│
  ┌─────────────────────────┬─────────────────────────┬───────────────┐
  │         ZONE 1          │         ZONE 2          │ OUTSIDE ZONES │
  │  (Above Bath / Shower)  │  (0.60 m Horizontal)    │ (Beyond 0.6m) │
  ├─────────────────────────┼─────────────────────────┤               │
  │         ZONE 0          │                         │   No 13A      │
  │   (Inside Tub / Basin)  │                         │   Sockets     │
  │                         │                         │  Within 3m    │
  └─────────────────────────┴─────────────────────────┴───────────────┘

Zone 0

• Definition & Boundaries: The interior volume of the bath tub or shower basin. For showers without a basin, Zone 0 is bounded by the floor level and a height of $0.10\text{ m}$ above the floor, extending to a horizontal radius of $1.20\text{ m}$ from the fixed shower head.
• Minimum Ingress Protection: IPX7 (protection against temporary immersion in water).
• Permitted Supply Voltage: Safety Extra Low Voltage (SELV) only, with a nominal voltage not exceeding 12 V AC (rms) or 30 V DC (ripple-free). The safety isolating source (transformer) MUST be located outside Zones 0, 1, and 2.
• Permitted Equipment: Only fixed electrical appliances specifically designed for use inside a bath tub or shower basin (e.g., specialized whirlpool jets or low-voltage underwater luminaires) rated IPX7.

Zone 1

• Definition & Boundaries: Bounded by the finished floor level and a horizontal plane corresponding to a height of 2.25 m above the floor (or the highest fixed shower head if installed higher than $2.25\text{ m}$). Horizontally, Zone 1 is bounded by the outer perimeter of the bath tub or shower basin (or a $1.20\text{ m}$ radius for basin-less showers).
• Minimum Ingress Protection: IPX4 (protection against splashing water). If the location is subject to high-pressure cleaning water jets (e.g., communal/commercial shower facilities), IPX5 is mandatory.
• Permitted Supply Voltage: SELV or PELV with nominal voltage not exceeding 25 V AC or 60 V DC.
• Permitted Equipment: Only fixed, permanently connected water heaters, shower pumps, whirlpool units, ventilation fans, and SELV/PELV luminaires suitable for Zone 1 and rated IPX4 minimum.

Zone 2

• Definition & Boundaries: Bounded by the vertical boundary of Zone 1 and a parallel vertical plane located 0.60 m (600 mm) horizontally outside Zone 1. Vertically, it extends from the floor up to a height of 2.25 m.
• Minimum Ingress Protection: IPX4 (or IPX5 if cleaning jets are used).
• Permitted Equipment: Luminaires, exhaust fans, heated towel rails, and shaver supply units complying with BS EN 61558-2-5 (which contain a safety isolating transformer).

Outside Zones (Beyond Zone 2)

• Any space extending beyond Zone 2 ($>0.60\text{ m}$ from Zone 1) up to the physical boundaries of the room.
• General Equipment: General luminaires and switches may be installed outside Zone 2, provided they are protected by an RCD.
• 13 A Socket Outlet Rule: Standard 13 A socket outlets (conforming to BS 1363) are STRICTLY PROHIBITED within 3.0 meters measured horizontally from the boundary of Zone 1.

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Summary of Zone Rules & Technical Specifications

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RCD and Bonding Requirements for Bathrooms

1. Mandatory 30 mA RCD Protection: According to BS 7671 Regulation 701.411.3.3, ALL low-voltage final circuits supplying electrical equipment or passing through a room containing a bath or shower MUST be protected by a 30 mA Residual Current Device (RCD) with automatic disconnection within $40\text{ ms}$ at $5 I_{\Delta n}$.
2. Supplementary Equipotential Bonding: Local supplementary bonding must connect together all exposed-conductive-parts of equipment in Zones 1 and 2 to all extraneous-conductive-parts (metallic hot/cold water pipes, waste pipes, structural steelwork).
   • Exemption Clause: Supplementary bonding may be omitted if three conditions are simultaneously satisfied:
     • All final circuits meet main automatic disconnection of supply ($Z_s$ limits).
     • All final circuits in the location are 30 mA RCD protected.
     • All extraneous-conductive-parts are reliably connected to the main protective earthing conductor.