What cable size do I need for a hot tub?

Most 32A hot tubs need 6mm² SWA cable for runs up to about 18m, or 10mm² for longer runs. Check your specific hot tub rating - some larger models need 40A supply with 10mm² cable minimum. Always calculate voltage drop for your cable length.

Can I plug a hot tub into a normal socket?

Some small hot tubs have 13A plugs and can use a standard socket. However, most quality hot tubs require 32A hardwired supplies. Even 13A hot tubs benefit from dedicated circuits as they run continuously and can trip shared circuits. Check manufacturer requirements.

Do I need an outdoor isolator switch for a hot tub?

Yes, BS 7671 requires a means of isolation within sight of the hot tub - typically a weatherproof rotary isolator switch. This allows emergency disconnection without entering the house. Position within 3m of the tub, at least 2m from the water edge.

What RCD protection is required for hot tubs?

30mA RCD protection is mandatory for all hot tub circuits. Type A RCD minimum (detects AC and pulsating DC faults). Some manufacturers recommend Type B RCDs for units with variable speed pumps. The RCD can be at the consumer unit or in a local enclosure.

Why do hot tubs need dedicated circuits?

Hot tubs draw significant continuous current (up to 32A) for heating. Sharing circuits causes voltage drop, nuisance tripping, and potential overheating. Dedicated circuits ensure reliable operation and comply with manufacturer installation requirements for warranty validity.

How far can I run cable to a hot tub?

Distance is limited by voltage drop. At 32A, 6mm² cable drops about 7.3mV per amp per metre. A 20m run drops 4.7V (2%). Runs over 25-30m typically need 10mm² to keep voltage drop acceptable. Our calculator checks this automatically.

Can I install hot tub electrics myself?

No, hot tub installation is notifiable work under Part P Building Regulations. It involves outdoor circuits and requires qualified electrician certification. DIY electrical work on hot tubs is illegal, voids insurance, and can be lethal. Always use a registered electrician.

What about swim spas - do they need more power?

Yes, swim spas have powerful jet pumps plus heaters and often need 40A-63A supplies. Some require three-phase power. Check manufacturer specifications carefully. Cable sizes of 10mm² or 16mm² are common for swim spas. Plan supply capacity before purchase.

Do I need to notify the DNO for hot tub installation?

Not usually for standard 32A installations on existing domestic supplies. However, if adding significant load to a property near its supply limit, or if requiring supply upgrade, DNO notification may be needed. Your electrician can advise based on your specific situation.

What IP rating do outdoor electrical connections need?

Outdoor isolators and connection points need minimum IP65 (jet water protected) for hot tub installations. IP66 or IP67 is preferred for areas near water. All outdoor electrical equipment must be suitable for the conditions and properly sealed.

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Hot Tub & Spa Cable Sizing Calculator

Calculate the correct cable size for hot tub, spa, and swim spa installations

Hot Tub Cable Quick Facts

Most hot tubs need 32A circuit with 6mm² or 10mm² cable
Large swim spas may need 40A or 63A supply
30mA RCD protection mandatory - Type A minimum
Outdoor isolator switch required within sight of spa
SWA cable typically required for outdoor runs

Cable Size Calculator

BS 7671:2018+A2:2022 compliant

1. Load Current

2. Cable Length (meters)

3. Installation Method

Lighting circuit (3% voltage drop limit)

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Common Hot Tub Installations

Standard hot tub (13A plug-in)

Can use existing socket, but dedicated circuit preferred for reliability

Hot tub 3-5 person (32A hardwired)

32A circuit, 6mm² SWA for runs under 18m, 10mm² for longer

Large hot tub 6-8 person

32A or 40A circuit, 10mm² SWA recommended for voltage drop

Swim spa / exercise pool

40A-63A circuit depending on heater size, 10mm² or 16mm² SWA

Multiple units (hot tub + sauna)

Separate circuits recommended, or submain to outdoor consumer unit

Complete Your Outdoor Living Space

Hot tubs pair perfectly with sauna installations for complete home wellness. Consider adding swimming pool electrical for the ultimate garden setup. For garden rooms housing your hot tub, check our garden building guide.

Hot Tub Cable Sizing

Hot tub cable sizing determines the conductor cross-sectional area (mm²) needed to safely supply a spa or hot tub. Most UK hot tubs draw 13-32A continuously when heating. Cable must handle continuous load without overheating and keep voltage drop under 5% for reliable operation. Outdoor installation requires SWA cable and weatherproof isolator.

Hot Tub Installation Costs (2024)

Typical UK installation costs including SWA cable, isolator, and labour. Excludes hot tub cost.

Installation Scenario	Materials	Labour	Total
Hot tub, short run (<10m)	£120-200	£200-300	£320-500
Hot tub, medium run (10-20m)	£200-350	£280-400	£480-750
Hot tub, long run (20-35m)	£350-550	£350-500	£700-1050
Swim spa (40A+ supply)	£400-700	£400-600	£800-1300
Outdoor isolator switch	£40-80	£60-100	£100-180

Prices as of 2024. Actual costs vary by region, cable run length, and ground conditions.

Hot Tub Electrical Requirements

Hot tubs require dedicated electrical supplies with specific safety features: 30mA RCD protection (Type A or AC minimum), rotary isolator switch within sight of the tub (3m maximum), and weatherproof connections. The circuit must handle continuous heating load - hot tub heaters run for extended periods maintaining temperature.

Continuous Load Consideration

Hot tubs operate under continuous load conditions - heaters run for extended periods maintaining water temperature. BS 7671 requires cables for continuous loads to be derated or oversized. A 32A continuous load should be treated as requiring higher capacity than intermittent 32A loads. Most hot tub cable sizing already accounts for this.

Zone Requirements for Swimming Pools

BS 7671 Section 702 defines zones around swimming pools, hot tubs and spas. Zone 0 is inside the vessel (no electrical equipment). Zone 1 extends to surrounding area. Zone 2 extends 1.5m beyond Zone 1. Different equipment types and IP ratings are permitted in each zone. Hot tub installations must comply with these zone requirements.

Frequently Asked Questions

Related Electrical Calculators

Voltage Drop Calculator

Essential for outdoor hot tub cable runs

Cable Sizing Calculator

Full BS 7671 cable sizing for all circuits

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