Bubbles Are the Easy Bit: Sorting the Garden Supply Before the Spa Lands

There’s a moment, usually about a week before delivery, when the hot tub stops being a nice idea and becomes a very large object with a delivery slot. That’s also the moment someone asks, "Can we just run an extension lead out there?" Short answer: no. Longer answer: no, and please don’t. A hot tub is a wet, outdoor, high-load appliance. It deserves a proper circuit, not a daisy chain of garden flex.

This isn’t about taking the fun out of it. Bubbles are excellent. But the electrical plan should start before the spa is wheeled down the side passage, because retrofitting a supply after the deck is built is the sort of job that turns a relaxing purchase into a patio archaeology project.

The spa doesn’t run on vibes — it needs its own circuit

Many hot tubs draw serious current: heaters, pumps, blowers and controls can add up. Some smaller models run from a 13A plug, but even those need a safe outdoor supply with the right protection. Larger spas often need a dedicated circuit sized for the manufacturer’s stated load, with cable and protective devices chosen to suit. That means no sharing with the shed lights, no plugging into the kitchen ring via a long orange lead, and no assuming the existing outdoor socket is "probably fine".

A dedicated circuit gives you a clean supply that can be isolated, tested and protected on its own. It also means a fault in the spa doesn’t take out half the house — or, worse, leave a live cable lying across wet grass.

Check the consumer unit before you check the bubbles

Before anyone digs a trench, look at the consumer unit. Does it have spare ways? Is there RCD protection? What’s the existing load like? A hot tub added to an already busy supply can push things close to the limit, especially if you’re also running an EV charger, heat pump, electric shower or garden office.

A proper load check isn’t about guessing from the size of the house. It’s about looking at the supply capacity, the existing circuits and the spa’s requirements together. If the board is full, old, or has a history of tripping, that’s a conversation to have now — not on the day the water starts heating.

RCD, RCBO and the protection that actually matters

Outdoor electrical equipment needs reliable earth fault protection. In practice, that usually means a 30mA RCD or RCBO protecting the circuit. An RCBO combines overcurrent and earth fault protection in one device, which can be neater and means a trip is less likely to knock out unrelated circuits. Either way, the protection needs to be correct for the circuit and tested.

Don’t rely on a plug-in RCD as a substitute for a properly designed circuit. It can be a useful extra layer for portable equipment, but it isn’t a plan for a permanent outdoor appliance. The same goes for "it worked at the old house" — electrical arrangements don’t travel well.

The cable route is part of the design

Armoured cable is common for garden supplies because it can handle the rigours of outdoor life, but it still needs to be installed properly. That means the right size for the load and voltage drop, a sensible route, adequate depth where buried, and protection where it emerges. It also means thinking about the mower, the strimmer, the patio edging and the fact that someone will eventually plant a shrub exactly where you least want them to.

Keep the route away from water features, drainage runs and future deck posts. If the cable is going under a patio or path, plan for that before the hardcore goes down. A little drawing now saves a lot of head-scratching later.

The isolator should be outside, dry and reachable

An outdoor isolator gives you a way to cut the supply at the spa without marching back through the house in wet shoes. It should be in a suitable enclosure, positioned so it’s reachable but not sitting in the splash zone. The exact position depends on the spa and the manufacturer’s instructions, but "balanced on a plant pot" is not a recognised mounting method.

Make sure the enclosure is appropriate for outdoor use and that cable entries are properly sealed. Water and electricity can share a garden, but they should not share an enclosure.

IP ratings without the alphabet soup

IP ratings tell you how well an enclosure resists dust and water. For outdoor spa equipment, you’ll see various IP numbers quoted. The important thing is that the enclosure suits the location and the manufacturer’s requirements. An IP65 box in a sheltered spot is a different proposition from a cheap indoor socket under a dripping gutter.

Don’t assume a higher number is always necessary or always sufficient. The installation details matter: cable glands, seals, mounting height, drainage and whether the thing is actually protected from direct spray.

The pre-delivery checklist

Before the spa lands, sort the following:

• Confirm the hot tub’s electrical requirements from the manufacturer’s data.
• Ask a registered electrician to assess the consumer unit and supply capacity.
• Agree the cable route, isolator position and enclosure type.
• Check whether the work needs building control notification in your part of the UK.
• Book the electrical work before the delivery date, not after.
• Keep the manufacturer’s instructions and test certificates with your home paperwork.

When to call it in

If you’re unsure about load, cable size, RCD protection or bonding, call a registered electrician. Hot tubs are one of those purchases where the electrical bit is easy to underestimate. The good news is that a properly planned supply is straightforward, tidy and safe — and it lets you enjoy the bubbles without wondering what’s happening under the deck.

Get the circuit right first. Then get in the water.