What's involved in wiring a pergola electrical supply

Helpful video reference. We use the Electricians Vlog UK video "This Is The Ultimate Outdoor Pergola Hot Tub Area!!" as the video reference here. It walks through a real UK outdoor installation covering the cable route, weatherproof accessories, and RCD protection choices for a pergola and hot tub area.

1. Decide what you want to run at the pergola

List every load: outdoor LED lighting, one or two socket outlets, a garden sound system, a hot tub. Total the wattages and divide by 230 to get the current in amps. That figure sets the minimum RCBO rating at the house end.

For most pergolas with lighting and two sockets, a 20 A circuit is plenty. If you are adding a hot tub at the same time, the tub needs its own dedicated circuit sized to the manufacturer's data sheet - do not share a single circuit between the hot tub and the general accessories.

2. Work out the cable route

How you get the cable from the house to the pergola depends on whether the pergola is attached to the house or freestanding in the garden.

• Attached pergola: surface-mount grey or white conduit along the external wall and up to the pergola rafters, using saddle clips every 500 mm on the straight runs. Keep conduit runs vertical or horizontal, not diagonal.
• Freestanding pergola: bury a steel wire armoured (SWA) cable underground from the house to the pergola. Measure the full route length (including the rise out of the house and into the pergola) before ordering cable.

Avoid running cables in a way that could be damaged by garden tools, lawnmowers or strimmer cord. If the cable travels across a lawn at any point, underground SWA is the only sensible option.

3. Notify building control

In England, installing a new electrical circuit from a consumer unit is notifiable under Part P of the Building Regulations. You have two options: use a Part P registered electrician who will self-certify and notify the local authority after the work is complete, or submit a building notice to your local authority before you start and pay the inspection fee (typically £150 to £300).

Either way, you need an Electrical Installation Certificate at the end. This matters for your home insurer and for any future buyer. Do not let it slip.

4. Choose the right cable

For an attached pergola with conduit runs, 2.5 mm² PVC twin-and-earth in conduit is standard for a 20 A socket circuit. For underground runs to a freestanding pergola, you need SWA. Size it for voltage drop as well as current: for runs longer than about 20 metres at 20 A, 4 mm² SWA keeps the voltage drop below the 3% limit in BS 7671.

Order the SWA cable once you have confirmed the actual route length - not the straight-line distance. Cable is cheap; having to dig the trench again because you ran short is not.

5. Dig the trench for a buried run

SWA for a garden pergola supply must be buried at the correct depth:

• Open garden soil: 600 mm minimum depth.
• Under a path, patio or lawn: 450 mm minimum, with cable protection tiles laid directly above.
• Under a driveway: 900 mm minimum, or run in heavy-duty conduit.

Lay a marker tape 150 mm above the cable at whatever depth you choose. Sketch the route with measurements from fixed reference points (house corner, fence post) and keep that sketch with the property papers. Future you, or the next owner, will be grateful when they need to dig near the cable.

6. Fit weatherproof accessories

Every socket outlet used outdoors must carry a minimum IP44 rating under BS EN 60529. IP44 resists splashing water from any direction. For a particularly exposed pergola, or one with overhead water features, choose IP65 accessories instead.

Outdoor socket covers (the hinged lids you see on external sockets) are not IP-rated in themselves - the whole accessory assembly must carry the IP rating. Buy products that state the IP rating on the box, not ones where the IP claim only applies with the lid closed.

For outdoor lighting, choose luminaires rated IP44 or above. Festoon lights specifically designed for outdoor use usually carry IP44 as standard - check the rating on the packaging.

7. Consider earthing if the pergola is a separate structure

If your house supply is TN-C-S (also called PME - Protected Multiple Earthing, identified by a combined neutral and earth at the meter tail or meter box), you cannot extend that earth to a separate structure in the garden. A neutral fault at the distribution transformer can raise a PME earth to a dangerous voltage on any metalwork connected to it.

For a pergola that is physically attached to the house with no gap, the PME earth is fine to extend. For a freestanding structure any distance from the house, the answer is a local TT earth rod driven into the ground near the pergola, with the earth connected back to the main earth terminal at the consumer unit (or via the SWA armour, which must also be connected to earth at both ends).

Your electrician will check your earth type at the meter before advising you on this. It is one of the most common misunderstood points in outbuilding wiring.

8. RCBO at the consumer unit, test, and certify

The circuit needs a 30 mA RCD and an overcurrent protective device at the consumer unit. An RCBO combines both in one slot - it is the cleanest solution. A 20 A or 32 A RCBO depending on your load calculation fits in a standard DIN-rail consumer unit.

Before the circuit is energised, the electrician will carry out the required tests under BS 7671: polarity check, insulation resistance (between live and earth with the circuit de-energised), and earth fault loop impedance after energising. The results go on the Electrical Installation Certificate.

When to call us

The consumer unit connection at the house end is not DIY work. If you want to run the conduit yourself and pull the cable through, that is fine - but the terminations at both ends, the RCBO fitting, and the testing all need a registered electrician who can issue the certificate. Richard covers Sandwich and east Kent and is set up for exactly these jobs.