How to wire a conservatory electrical supply

Helpful video reference. This video covers the first-fix stage of a conservatory rewiring project from the perspective of a UK domestic electrician. It shows the cable runs, back box positions and early decisions that shape everything which follows — useful background before you plan your own conservatory supply.

1. Confirm the job is notifiable under Part P

Any new circuit anywhere in a dwelling — including a conservatory — is notifiable under Part P of the Building Regulations in England and Wales. Scotland has equivalent requirements under the Scottish Building Standards.

You have two routes. Hire a registered competent electrician who self-certifies the completed work. Or notify your local authority building control before starting, pay the relevant fee and arrange an inspection of the finished installation.

Adding a spur to an existing socket circuit rather than creating a new circuit may not be notifiable, but the safest approach is always to confirm with your local authority if you are unsure.

2. Plan the supply route

Identify a spare way in the main consumer unit for the conservatory circuit. If there is no spare way, you will need either a new consumer unit or a piggyback arrangement — both of which should be done by an electrician.

Measure the run from the consumer unit to the conservatory. For runs up to around 15 metres with a modest load (a few sockets and lights), 6 mm² SWA two-core with earthed armour is often adequate. For longer runs or higher loads, 10 mm² may be needed. Run the voltage drop calculation using BS 7671 Appendix 4 or ask an electrician to size the cable properly for your specific load.

3. Choose and size the sub-board

A small consumer unit — six way is usually enough — with a 63 A or 80 A RCD feeding the busbars is the cleanest arrangement. Each circuit inside the conservatory then gets its own MCB: typically a 32 A for sockets, a 6 A for lighting, and if you are fitting an electric radiator or underfloor heating, a separate 16 A or 20 A circuit.

The feed from the main house consumer unit to the sub-board needs an MCB sized to the cable's current-carrying capacity — a 10 mm² SWA fed at 40 A is common. The SWA armour provides the circuit protective conductor back to the main earth terminal (MET) in the house.

4. Run armoured cable from the consumer unit

SWA (steel wire armoured) cable is the right choice for the supply run: mechanically robust, with its own earth path, and suitable for buried or surface runs.

• Surface on the house wall — clip with SWA saddles every 300 mm on straight runs and at every change of direction.
• Underground in open ground — at least 600 mm deep; in a driveway, at least 500 mm. Mark the route with cable tile and warning tape before backfilling.
• Under a concrete floor or in a frost zone — use conduit and increase burial depth if the cable is in the frost-risk zone near the conservatory footings.

Photograph the cable route before burying or concealing it. This is required for the as-fitted record and matters at every future EICR.

5. Terminate the SWA cable

SWA termination uses a cable gland to clamp the armour wires and form the earth connection at each end. The sequence:

1. Cut the outer sheath back cleanly using an armoured cable stripper.
2. Fan the armour wires and fold them back over the outer sheath.
3. Slide the cable gland over the armour and tighten the compression nut to grip the armour wires firmly.
4. Run an earth tail from the gland to the earth bar in the sub-board, or to the MET if terminating at the main board.
5. Strip the insulated cores and terminate to the correct terminals.

Both ends of the SWA need a gland — at the main consumer unit and at the conservatory sub-board. The armour is only earthed if both glands are fitted and connected.

6. Fit and wire the sub-board

Mount the conservatory consumer unit on a suitable surface — usually the house wall just inside the conservatory or on the adjoining internal wall. Connect the SWA line and neutral to the main switch input terminals, and the earth tail from the gland to the earth bar.

Fit MCBs or RCBOs for each planned circuit. If the main supply feed already has RCD protection, standard MCBs in the sub-board are sufficient. If the feed is unprotected (which should not happen on a modern installation), each sub-board circuit needs its own RCBO.

Label every MCB clearly before energising. A sticker on the inside of the board door listing what each way controls takes seconds and saves hours of detective work later.

7. First and second fix inside the conservatory

During first fix, run circuit cables to each socket and lighting position. In a timber-frame conservatory, cables typically run inside the frame members in oval conduit or clipped to the structure before cladding is fitted. Mark every cable run on the as-fitted drawings.

For socket positions, use flush or surface back boxes appropriate to the wall construction. Standard IP2X accessories are fine in most conservatories; if the space is particularly damp or used as a utility room, consider IP44 rated accessories.

In second fix, pull cables through, make connections at each accessory and fit faceplates. Keep cable loops tidy inside back boxes and avoid trapping insulation between the box edge and the faceplate.

8. Dead test before energising

With the sub-board switched off, carry out the dead tests required by BS 7671 Chapter 61:

• Continuity of every CPC (R1+R2 and Rn) for each circuit
• Insulation resistance at 500 V DC between all conductors and earth (minimum 1 MΩ per circuit)
• Visual verification of polarity before energising

Once every circuit passes dead testing, energise the sub-board and carry out live tests: loop impedance (Zs at each socket), polarity confirmation at each accessory and RCD trip time at the sub-board. Record all values on the Schedule of Test Results before signing the Electrical Installation Certificate.

When to call us

Conservatory wiring is one of the more common jobs Richard covers in east Kent — new supply circuits, sub-boards, sockets, lighting and the Part P certification that makes the work legal and insurable. If you are having a conservatory built in Sandwich, Deal or Dover and need the electrics done properly, get in touch.