Hot tub electrical installation, from the consumer unit to the tub.

What supply a hot tub needs

Most hard-shell tubs, the kind with a heater and jet pumps built in, are hard-wired on a 32 amp supply with a circuit to themselves. Smaller plug-in models and most inflatables are made for a 13 amp socket instead.

The installation sheet that came with your tub gives the exact supply and the type of RCD it needs, and I wire to that sheet as well as to BS 7671.

Nothing else should share the tub's circuit. A heater and pumps running for hours make a heavy, steady load, and a dedicated circuit keeps that load off a ring the kitchen or the garage also relies on.

The new circuit takes a spare way in your consumer unit. If there's no room on the board, replacing the consumer unit comes first.

Where the isolator and the cable go

The isolator goes on a wall or post near the tub, out of reach of anyone sitting in the water, so the power can be cut before the cover comes off for cleaning. Sockets and switches don't belong right beside the tub.

BS 7671 has no hot tub section, so IET guidance applies the swimming pool rules (Section 702) to a tub outdoors and the bathroom rules (Section 701) to one in a garden room or conservatory.

From the house, the circuit runs in steel wire armoured cable, clipped to a wall where it can. Across a lawn or a border it goes underground, deep enough that normal digging won't reach it, with warning tape laid above.

The trench isn't in the price, so whoever lays the base for the tub can often dig it at the same time, or we'll quote for it in writing.

Earthing, and the right type of RCD

A tub is earthed equipment holding water made more conductive by its sanitising chemicals, and the people using it are wet, which is why IET guidance treats it much like a swimming pool.

Many homes have a PME supply, where the earth comes from the network's combined neutral. If that neutral failed in the street, the tub's metalwork could rise towards mains voltage without an RCD seeing it. The network operators' guidance for pools (ENA G12/4) prefers a separate earth rod for that reason, and the IET says the same of hot tubs.

So at the survey I look at how the house is earthed and where the tub will stand. If it needs a separate earth rod, that goes into the written quote before any cable goes in.

The RCD type matters too. A pump's speed control can leak a little direct current, enough to stop a basic Type AC device tripping, so I fit the type the maker asks for.

Plug-in and inflatable hot tubs

A 13 amp tub still needs the right socket. IET guidance accepts one near a tub only where the maker allows it, RCD-protected and well back from the water.

If there's no socket outside, a weatherproof outdoor socket on the house wall does the job.

I'd rather not see any tub running from an extension lead out of a kitchen window. A heater pulls a steady current for hours, and a lead left coiled on its reel heats up as it does.

Building regulations for a hot tub circuit

A hot tub circuit counts as a new circuit, and in England new circuits are notifiable work under regulation 12(6A) of the Building Regulations 2010.

When the circuit has passed its tests, you get the Electrical Installation Certificate from me. Keep it with the tub paperwork.

Who connects the tub

Agree who does what with the tub supplier before anything is booked, because a certificate for the supply covers the supply and nothing beyond it. Some suppliers position and commission the tub themselves.

I wire the supply as far as the isolator, and make the last connection to the tub too if its instructions allow it.

Hot tubs at holiday lets

A tub at a holiday let is part of a business. HSE guidance HSG282 covers domestic-style hot tubs used that way, and the water treatment and record keeping it describes fall to the owner or operator.

The supply is wired and certified just as it would be at a family home. Static caravans are different, because the park usually owns the pitch supply, so ask the park before buying a tub for one.