How to Run Electricity to a Remote Cabin

Start with the load, not the cable

Before anyone picks up a spade, work out what the cabin will actually draw. Add up the watts: LED lighting, phone chargers, a small fridge, a laptop, a pump, perhaps a 2 kW heater or a kettle. You rarely run everything at once, so a sensible diversity calculation gives you a realistic design current. A 32 A supply at 230 V is roughly 7.3 kW and covers most cabins comfortably. A 16 A supply — about 3.7 kW — is ample for lights, devices and a fridge, but struggles the moment someone puts the kettle on while the heater is running.

The second number that matters is distance. Cable resistance rises with length, and voltage drop has to stay within the limits set out in BS 7671 — broadly 3 per cent for lighting and 5 per cent for other circuits. A 2.5 mm² armoured cable that is perfectly adequate at 20 metres can be well outside those limits at 60 metres. This is why cable sizing for a remote cabin is almost always about distance rather than current, and why guessing at the size is the most common and most expensive mistake.

Armoured cable earns its keep out of doors

Steel wire armoured (SWA) cable is the default choice for a buried submain, and rightly so. The galvanised wire armour provides the mechanical protection, and the outer PVC sheath shrugs off damp, frost and UV. It can be buried directly, clipped to a wall, or run through ducting — all three are acceptable in the right circumstances.

Two details separate a neat job from a bodge. The first is the gland kit: an SWA gland, a brass banjo washer and a fly lead, so the armour is properly terminated and earthed at both ends. The second is the bend radius — armoured cable does not appreciate being folded round a tight corner, and forcing it can crack the sheath and let water in.

• Two-core SWA uses the armour as the circuit protective conductor — simple and cost-effective.
• Three-core SWA carries a separate earth core, which is often preferred for longer runs and for installations where the armour may corrode.
• Burial depth of around 450–600 mm is the usual guidance, deeper under driveways or anywhere vehicles pass.

Trenching, ducting and the details people forget

A clean trench is a straight trench. Dig it deep enough, keep it as level as you can, and bed the cable on a 75 mm layer of sand or riddled soil. Backfill gently, then lay a warning tape or cable tile about 150 mm above the cable so that a future spade strike is preceded by a loud plastic rustle.

Where the cable surfaces — at the house wall and again at the cabin — protect the transition with a length of rigid conduit or a swept bend, sealed against water and insects. Fit an isolator at the house end so the whole submain can be switched off without disturbing the main consumer unit, and leave a draw cord in any duct so the next person has an easier day than you did.

• Photograph the trench before backfilling, with a tape measure in shot — future you will be grateful.
• Keep the run at least 600 mm away from gas, water and drainage services.
• Seal duct ends with a bung or expanding foam to stop water tracking into the cabin.
• Mark the route on a site plan and keep it with the paperwork.

Earthing and protection at the far end

This is where a qualified electrician earns their fee. On a TN-C-S (PME) supply, exporting the supplier's earth to a remote outbuilding is generally not acceptable, because a broken neutral can raise the earth potential of every exposed metal part out there. The usual solution is a local TT arrangement: an earth electrode driven at the cabin, coupled with a suitably rated RCD at the source.

In practice, that often means a 100 mA time-delayed RCD at the house end for fault protection, and a 30 mA RCD or RCBOs in the cabin's own small consumer unit for additional protection and to cover socket outlets. The cabin board should be a proper IP-rated enclosure, not a domestic unit screwed to a damp wall, and everything inside it should be labelled clearly.

If the cabin has a woodburner, a gas bottle or any other fuel, fit a carbon monoxide alarm. It has nothing to do with the electrics, but it belongs in the same conversation.

Who should do the work

Running a submain is notifiable work in England and Wales under Part P, and the rules differ in Scotland and Northern Ireland. In practice, you want an electrician registered with a competent person scheme, who can design, install, test and certify the job and notify building control on your behalf.

Be clear about what you want from them. A good electrician will ask about your intended use, calculate the volt drop, specify the cable size and protection, and give you an electrical installation certificate plus test results when they finish. If they simply ask how many sockets you want and start digging, ask more questions.

If mains power is genuinely impractical, a solar array with battery storage and an inverter can run lighting, a fridge and device charging very happily. It is a different design conversation — and one worth having before you order 60 metres of armoured cable.

Finishing touches that make it last

Fit IP-rated outdoor sockets rather than indoor ones behind a flap, use glands rather than grommets wherever cable enters an enclosure, and leave a service loop at both ends so future maintenance does not require re-terminating under tension. Label the isolator at the house, keep the certificates with the deeds, and book a periodic inspection every few years.

Do all that, and the cable you buried on a wet Saturday in March will still be quietly doing its job in twenty years' time — which is exactly what you want from a cabin at the bottom of the garden.