How to Run Electricity to a Garden Shed: SWA Cable, Depth and Rules

Updated October 2026 · Meteor Electrical guides · 11 min read

Sheds are increasingly used as garden offices, gyms and workshops, and all of them need a safe, permanent power supply. This guide explains how to get power to a shed: the armoured cable to use, how to size it for the distance, how deep to bury it, when you need a consumer unit in the shed, and the rules that apply.

How do you run electricity to a garden shed?

Outdoor circuits face moisture, ground movement and garden tools, so they need more care than indoor wiring. A typical installation follows these steps:

1. Plan the loads. List the lights, sockets, heaters and equipment the shed will need.
2. Design the circuit. The electrician checks the spare capacity at your consumer unit and works out the cable size, protective device and earthing arrangement.
3. Choose the route. Decide between an underground or overhead run, avoiding drains, pipes and tree roots.
4. Dig and lay the cable. Lay SWA cable in a trench at a suitable depth, with warning tape above it.
5. Terminate the cable. Fit outdoor-rated glands at each end and connect to the house board and a shed consumer unit or enclosure.
6. Fit the shed wiring. Install IP-rated sockets, switches and lighting inside and outside the shed.
7. Test and certify. The electrician tests the circuit, issues an Electrical Installation Certificate and notifies the work where required.

How much power does your shed need?

How you use the shed decides the size of the supply. A few LED lights need very little, while an electric heater in a garden office can draw 2kW to 3kW on its own. Sketch a floor plan with socket and light positions for your electrician.

These are typical examples only; your electrician will assess the actual loads and the spare capacity at your main consumer unit.

Overhead or underground: which is best?

For most gardens, an underground route is the better long-term choice.

An overhead cable must be properly supported, usually on a catenary wire, and kept high enough to stay clear of people, ladders and vehicles. Where the cable runs along the outside of a building, see our guide to outdoor cable conduit on external walls.

What cable do you need to run power to a shed?

Steel wire armoured (SWA) cable is the standard choice for a shed supply. Its galvanised steel armour protects the cores from spades and impact, and the outer sheath resists moisture and sunlight. You can browse our armoured cable range in the common sizes used for outbuildings.

2-core or 3-core SWA?

Many electricians use 3-core SWA for a shed supply, using the third core as the circuit protective conductor (CPC) alongside the armour. 2-core SWA can rely on the armour as the CPC, but only where the designer confirms the armour is adequate. Either way, the armour must be earthed through the gland at the supply end.

Glands for outdoor SWA

Each end of the cable is terminated with a gland that clamps the armour and seals the sheath. Outdoors and in damp sheds, use CW type glands with a shroud, which seal both the inner bedding and outer sheath. Our cable glands cover the common SWA sizes, and our SWA gland size guide explains how to match the gland to the cable.

What size armoured cable for a shed?

The right SWA size depends on the load, the length of the run and how the cable is installed. Over longer distances, voltage drop is usually what decides the size. BS 7671 generally allows a 5% drop for power circuits (about 11.5V on a 230V supply), measured from the origin of the installation, so the drop in the house wiring counts too.

The table shows approximate voltage drop for copper SWA in typical examples, using standard tabulated values. It is a guide, not a design.

So for a shed about 30m, or 100ft, down the garden, 2.5mm² SWA is often too small for a 20A load, and 4mm² is a common choice. A 32A supply to a garden office at that distance usually needs 6mm², and longer runs may need 10mm² or more.

How deep should armoured cable be buried?

BS 7671 does not give one fixed burial depth. It requires buried cables to be deep enough to avoid damage from any reasonably foreseeable disturbance of the ground, and to be marked with cable covers or warning tape. In practice, about 450mm is typical under domestic gardens.

Many homeowners dig the trench themselves. Agree the route and depth with your electrician first, then:

1. Mark the route and check for buried pipes, drains and other services before you dig.
2. Dig the trench to the agreed depth, keeping the base even and free of sharp stones.
3. Lay the SWA directly on a bed of sand or fine soil, or in underground ducting.
4. Cover it with more sand or fine soil, then lay warning tape about 150mm above the cable.
5. Leave the trench open until the electrician has inspected the cable, then backfill and compact it.

Ducting is not required for SWA, but it protects the cable and makes replacement much easier, especially under paths and drives. Our guide to underground cable conduit and ducting covers duct sizes and depths in more detail, and our SWA installation guide covers cutting, laying and glanding.

Do you need an RCD and a consumer unit in the shed?

Socket outlets rated up to 32A must have 30mA RCD protection, and in practice almost every shed circuit is RCD protected. An RCD cuts the supply within a fraction of a second if current leaks to earth, for example through damaged cable or a faulty tool.

Single circuit or a garage consumer unit?

A storage shed with one light and a couple of sockets can be fed as a single circuit from an RCBO in the house consumer unit. For a workshop or garden office with several circuits, the usual approach is an SWA sub-main from the house to a small garage consumer unit in the shed, with its own main switch and separate breakers for lighting, sockets and heating. Browse our consumer unit boards and RCDs and RCBOs, or read our guide to RCBO vs RCD and MCB consumer units.

Where there is an RCD at both ends, the electrician will arrange them so a fault in the shed does not trip the house, for example with a time-delayed RCD on the sub-main.

Earthing the shed

Earthing an outbuilding needs care, particularly on a PME (TN-C-S) supply. In some cases, such as a metal-framed building or a shed with a metal water pipe, the electrician may fit a separate earth electrode and treat the shed as a TT system.

Which outdoor sockets and lights should you use?

Sheds are often cold and damp. In an IP rating, the first number covers dust and solid objects and the second covers water.

Our weatherproof switches and sockets include IP-rated outdoor sockets for shed walls and garden areas, and our weatherproof switches and sockets buying guide explains IP ratings, cable entries and glands.

Shed and security lighting

LED battens and bulkheads give good light for very little power. Warm white (around 2700K to 3000K) suits a garden room, while cool white or daylight (around 4000K to 5000K) suits a workshop. For the outside of the shed, choose outdoor lighting rated IP65 or above, and consider PIR motion detectors or dusk-to-dawn sensors for security lighting on the path.

How do you get internet in a shed?

Mesh Wi-Fi or an outdoor access point is easy to set up and fine for browsing, but the signal can struggle over distance. For video calls, an outdoor-grade Ethernet cable is more reliable. Use cable rated for external or direct burial use, in its own duct kept apart from the power cable. If you are digging a trench anyway, lay a data duct at the same time.

Is running power to a shed notifiable? Part P and the rules

A new circuit to a shed or outbuilding is notifiable work in England and Wales under Part P of the Building Regulations. The simplest route is an electrician registered with a competent person scheme, who can self-certify the work. Otherwise, you must notify building control before work starts.

• England and Wales: a new outdoor circuit is notifiable under Part P.
• Scotland: electrical work is covered by the Scottish building standards system, so check with your local authority or electrician.
• Northern Ireland: Part P does not apply, but the work should still be carried out to BS 7671 and certified by a competent electrician.
• Republic of Ireland: the work should be done by a Registered Electrical Contractor and certified to I.S. 10101, the national wiring rules.

Planning permission is not usually needed just to run power to an existing shed. Whatever the location, you should receive an Electrical Installation Certificate, which you may need when you sell the house. The IET publishes BS 7671 and guidance for electricians.

Common mistakes to avoid

• Using an extension lead as a permanent supply. Leads get damaged, overloaded and wet.
• Burying twin and earth cable. It is not designed for burial and has no mechanical protection.
• Undersizing the cable for a long run. Voltage drop can leave equipment underpowered and breach BS 7671.
• Using indoor accessories in a damp shed. Choose IP-rated or metal-clad sockets and switches.
• Not getting the work certified. Uncertified work can cause problems with building control, insurance and house sales.

Running electricity to your garden shed the right way

Knowing how to run electricity to a garden shed comes down to a few essentials: SWA armoured cable sized for the load and distance, buried at a safe depth with warning tape, RCD protection and IP-rated accessories. Plan your power needs early, agree the design with a qualified electrician and make sure the work is tested and certified.

Need help choosing? Call our team on 028 8675 1515 (048 from ROI), Monday to Friday, 8am–5pm.

FAQs

What size armoured cable do I need for a shed 30m (100ft) away?

For a shed about 30m away, 4mm² SWA is a common choice for a 20A supply, and 6mm² for a 32A supply to a garden office. 2.5mm² usually suits shorter runs with light loads. The final size must come from a BS 7671 design that checks voltage drop, load and earth fault loop impedance.

How deep should armoured cable be buried to a shed?

BS 7671 does not set a fixed depth, but SWA must be buried deep enough to avoid damage. Around 450mm is typical under lawns and flower beds, with more depth under drives and cultivated ground. Lay warning tape or cable covers above the cable and record the route.

Do I need a consumer unit in my shed?

Not always. A shed with a few lights and one or two sockets can run as a single circuit from the house. A shed with several circuits, such as lighting, sockets and a heater, usually gets a small garage consumer unit fed by an SWA sub-main from the house board.

Can I run an extension lead to my shed?

Only as a short-term, temporary measure with an RCD-protected outdoor lead that is fully uncoiled and kept out of the way. An extension lead left in place is easily damaged, is not weatherproof at the connections and is not a safe permanent supply. Use a properly installed circuit instead.

Is running electricity to a shed notifiable under Part P?

Yes, in England and Wales a new outdoor circuit to a shed is notifiable, so use an electrician registered with a competent person scheme or notify building control. In the Republic of Ireland, use a Registered Electrical Contractor. You should receive an Electrical Installation Certificate for the work.

Does armoured cable need to go in conduit or ducting?

No. SWA is designed for direct burial and does not need ducting. Many electricians still lay it in underground ducting because it protects the cable and makes it easier to replace later. Ducting is especially useful under paths, patios and drives where digging up the route again would be difficult.

Related guides

• Underground cable conduit and ducting: UK depths, cable and duct guide
• Outdoor cable conduit: choosing and fitting conduit on external walls
• SWA armoured cable installation guide
• What size of SWA gland do you need?