Hot Tub Electrical Requirements: Supply, RCD Protection & Installation

Electrical requirements for hot tub installations — supply sizing, RCD protection, cable selection, and BS 7671 compliance.

10 min read Guide J. Clarke, Qualified Electrical TrainerLast reviewed: March 2026

Hot Tub Electrical Overview

Hot tubs are increasingly popular in UK homes, but they come with significant electrical requirements that must not be underestimated. A hot tub is a high-power appliance that combines water and electricity — two things that demand the utmost respect and strict compliance with BS 7671 (the IET Wiring Regulations).

A full-size hot tub typically draws between 25A and 40A, requiring a dedicated electrical supply from the consumer unit. This is not a DIY job. The installation must be carried out by a qualified electrician and is notifiable under Part P of the Building Regulations. For general outdoor electrical regulations, see our dedicated guide. Any electrician undertaking this work must be competent in outdoor electrical installations and familiar with the specific requirements for supplies to equipment in proximity to water.

Professional Installation Required

Hot tub electrical installation must be carried out by a qualified, registered electrician. It is notifiable work under Part P of the Building Regulations. Attempting a DIY installation is illegal (if not notified to building control) and extremely dangerous due to the combination of high current and water. An Electrical Installation Certificate (EIC) must be issued on completion.

Supply Requirements

The electrical supply required for a hot tub depends on the size and specification of the unit. Always check the manufacturer documentation for the exact electrical requirements before specifying the installation.

Full-Size Hot Tubs (Hardwired)

Most full-size hot tubs with multiple pumps and a heater require a dedicated 32A or 40A supply hardwired from the consumer unit. These cannot be connected via a standard plug and socket. The supply must be on its own dedicated circuit with appropriate overcurrent and RCD protection at the consumer unit.

✓32A supply: suitable for most standard hot tubs (up to approximately 7kW)
✓40A supply: required for larger hot tubs with multiple pumps or higher-rated heaters
✓Always verify the required supply rating from the manufacturer documentation
✓The circuit must be dedicated — not shared with any other load
✓A spare way at the consumer unit is needed, or the board may need upgrading

Plug-In Hot Tubs (13A)

Some smaller, inflatable or portable hot tubs are designed to operate from a standard 13A socket. These are significantly lower powered (typically 1.5kW to 2kW) and heat much more slowly. While these do not require a dedicated hardwired supply, the socket used should be RCD protected and the plug must incorporate a residual current device. The socket must not be within reach of the hot tub.

Check Before You Quote

Always obtain the hot tub manufacturer specifications before quoting. The data plate or installation manual will state the required supply (amps), cable size, and any specific requirements. Never assume a 32A supply is sufficient — some larger hot tubs with multiple pumps and auxiliary heaters require 40A or more.

Cable Selection

Correct cable selection is essential for safety and compliance. The cable must be rated to carry the required current for the full length of the run without exceeding the voltage drop limits specified in BS 7671.

Cable Sizes

✓32A supply: 6mm² twin and earth (T&E) cable for internal runs within the building
✓40A supply: 10mm² twin and earth (T&E) cable for internal runs
✓SWA (Steel Wire Armoured) cable must be used for any cable running externally or underground
✓Underground cable must be buried at a minimum depth of 500mm (or 600mm under areas with vehicular access)
✓Cable buried underground should be laid on a bed of sand with cable tiles or warning tape above

Voltage Drop

Hot tubs are often installed at the far end of a garden, resulting in long cable runs. For longer runs, the voltage drop must be calculated to ensure it stays within the 5% limit for a final circuit (11.5V for a 230V supply). If the voltage drop exceeds this limit, the cable size must be increased. For example, a 32A circuit on a 30-metre run may require 10mm² cable instead of 6mm² to keep within the voltage drop limits.

SWA Cable for External Runs

Standard T&E cable is not suitable for external or underground installation. Use SWA (Steel Wire Armoured) cable for any section of the cable route that runs outside the building or underground. SWA cable provides mechanical protection and can be direct buried (though protective measures such as sand bedding and cable tiles are still required). The SWA armouring can be used as the circuit protective conductor (CPC) where correctly terminated.

RCD Protection

RCD (Residual Current Device) protection is a critical safety requirement for any hot tub installation. The combination of water, electricity, and human contact makes earth fault protection essential.

Minimum Requirements

✓30mA RCD protection is mandatory for the hot tub circuit
✓Type A RCD as a minimum — required because hot tubs contain electronic controls, variable-speed pumps, and heater elements that may produce pulsating DC fault currents
✓A dedicated RCBO at the consumer unit is the cleanest and most reliable approach
✓The RCD must disconnect the supply within the required time (typically 40ms at 150mA for a 30mA device)
✓Additional RCD protection at the local isolator is recommended as a secondary measure

Type A RCD Is the Minimum

A Type AC RCD is not sufficient for hot tub installations. Hot tubs contain electronic components, pump inverters, and heater controls that can produce pulsating DC residual currents. A Type AC RCD may not detect these fault currents. A Type A RCD (or higher, such as Type F or Type B) is required to ensure reliable fault detection and disconnection.

The most practical approach for most installations is to use a dedicated RCBO at the consumer unit. This provides both 30mA RCD earth fault protection and overcurrent protection (32A or 40A MCB equivalent) in a single device, dedicated solely to the hot tub circuit. This eliminates the risk of a hot tub fault tripping an RCD that also serves other circuits.

Local Isolation

A local means of isolation is required for any hot tub installation. This allows the supply to be disconnected quickly in an emergency without having to access the consumer unit inside the property.

Isolator Requirements

✓A lockable rotary isolator switch must be installed on the supply to the hot tub
✓The isolator must be within sight of the hot tub so the user can confirm it is off
✓It must NOT be reachable by someone in the hot tub — minimum 2 metres from the tub edge
✓The isolator must be rated for the full load current of the circuit (32A or 40A minimum)
✓An IP65-rated enclosure is recommended for outdoor isolators to protect against weather
✓The isolator should be double-pole, disconnecting both line and neutral

Emergency Disconnection

Position the isolator where it is easily accessible but cannot be reached by someone in or entering the hot tub. A common approach is to mount it on the wall of the house at a height of approximately 1.2m, within clear sight of the hot tub location. Ensure there are no obstructions (fences, sheds, planting) between the isolator and the tub that would prevent it being seen or accessed quickly.

Outdoor Installation Considerations

Most hot tubs are installed outdoors, which introduces additional electrical requirements beyond those for an internal installation.

Enclosures and IP Ratings

✓All external electrical connections and equipment must use IP-rated enclosures suitable for the location
✓IP65 minimum for outdoor isolators and junction boxes
✓Cable entries must be properly sealed to maintain the IP rating of the enclosure
✓Avoid running cables across paths or areas where they could be damaged

Cable Routing

✓SWA cable for all external and underground cable runs
✓Underground cables must be buried at minimum 500mm depth (600mm under driveways or areas with vehicular access)
✓Lay cables on a bed of fine sand or sifted soil with cable tiles or warning tape placed above
✓Route cables to avoid future excavation areas (flowerbeds, planned extensions)
✓Keep cable routes away from other services (gas, water, drainage) with appropriate separation distances

Site Considerations

Before installing the electrical supply, consider the practical aspects of the hot tub location. The base must be level and strong enough to support the filled weight (a full-size hot tub can weigh over 1,500kg when filled with water and occupied). Adequate drainage is essential — hot tubs need periodic draining and may splash or overflow. Ensure there is clear access for future maintenance and that the electrical supply route does not obstruct access to the hot tub equipment compartment.

Testing and Certification

Hot tub electrical installations must be fully tested and certified in accordance with BS 7671. Proper earthing and bonding is critical for outdoor water-related installations. The work is notifiable under Part P of the Building Regulations, meaning it must be reported to the local authority building control (or self-certified by an electrician registered with a competent person scheme).

Required Tests

✓Continuity of protective conductors (including any SWA armouring used as CPC — see our electrical safety at home guide)
✓Insulation resistance (minimum 1 megohm at 500V DC between live conductors and earth)
✓Earth fault loop impedance (Zs must be low enough to ensure disconnection within the required time)
✓RCD operation time (must trip within 40ms at 5x rated residual current, i.e. 150mA for a 30mA device)
✓Polarity check on all connections
✓Prospective fault current measurement

Certification and Notification

✓An Electrical Installation Certificate (EIC) must be issued — a Minor Works certificate is not appropriate for a new circuit
✓Part P notification must be submitted to building control
✓If registered with NICEIC, NAPIT, or similar scheme, the electrician can self-certify and notify
✓If not registered, the homeowner must arrange a building control inspection before the circuit can be energised
✓Keep a copy of the EIC with the property records — it may be required for house sales or insurance claims

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Frequently Asked Questions

Can I install a hot tub myself?

You can physically position the hot tub yourself, but the electrical connection must be carried out by a qualified electrician. Hot tub electrical installation is notifiable under Part P of the Building Regulations, meaning it must be certified and reported to building control. Only a registered electrician (through a competent person scheme such as NICEIC or NAPIT) can self-certify this work.

Do I need a dedicated circuit for a hot tub?

Yes. Most full-size hot tubs require a dedicated circuit from the consumer unit, typically rated at 32A or 40A depending on the manufacturer specifications. This circuit must not be shared with any other appliance. Smaller plug-in hot tubs (sometimes called lay-z spas) may use a standard 13A plug, but these are limited in power and heating capability.

What type of RCD protection does a hot tub need?

A hot tub requires 30mA RCD protection as a minimum. Because hot tubs contain electronic controls, pumps, and heaters that may include rectified circuits, a Type A RCD is the minimum requirement. The cleanest approach is a dedicated RCBO at the consumer unit, providing both RCD and overcurrent protection on a single device for the hot tub circuit.

How far should the isolator switch be from the hot tub?

The local isolator switch must be within sight of the hot tub but not reachable by someone in or standing immediately beside the tub. A minimum distance of 2 metres from the hot tub is the general recommendation. This ensures the supply can be disconnected in an emergency without risk of someone in the water operating the switch.

How much does it cost to have a hot tub wired in?

A typical hot tub electrical installation costs between 400 and 800 pounds, depending on the distance from the consumer unit, the cable route, and whether any upgrades to the existing installation are needed. This includes the dedicated circuit, isolator switch, cable, testing, and certification. Longer cable runs requiring SWA cable or trenching for underground runs will increase the cost.

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