How to upgrade a single socket to a double socket

Video reference. The tutorial above is from eSpares, "How to Change a Single Socket to a Double Socket (UK 3-Pin)". eSpares is a UK parts and advice company whose electrical guides cover BS 1363 wiring practice throughout. Watch it fully before you start — the back box depth issue is covered clearly.

1. Isolate at the consumer unit

Find the MCB or fuse protecting the ring final circuit that feeds the socket. Switch it off. In an older split-load board the socket ring is typically on the RCD side — switch both the RCD and the MCB if your board has that layout. Confirm dead at the socket faceplate with a voltage indicator or approved tester. Dead on both pins? Carry on.

2. Photograph the wiring before disconnecting

Undo the two faceplate screws, ease the plate away from the wall (it will still be attached by the cables), and take a sharp photo of the terminal block with all conductors in place. If there is more than one set of cables — which is normal on a ring — photograph the whole arrangement carefully. This picture is your safety net for the next step.

3. Check the back box depth

Look inside the recess while the faceplate hangs free. Standard flush back boxes are 25 mm deep. A typical double gang faceplate needs 35 mm to accommodate the terminals without crushing the conductors. You can often read the depth stamped on the inside of the plastic or metal box.

• If the existing box is already 35 mm (or deeper), the new double faceplate will fit straight onto the same fixings.
• If the box is 25 mm, you have two options: chisel the plaster recess deeper and fit a 35 mm box, or fit a surface-mount double pattress that sits proud of the wall without any plastering.
• On a dry-lined wall (plasterboard), a dry-lining box with wings is your best option — no chiselling needed.

Buying a double faceplate and hoping the depth works out is the most common mistake in this job. Measure first.

4. Disconnect carefully, one conductor at a time

Loosen the first terminal, withdraw the conductor, and lay it somewhere it will not touch anything live. Then move to the next. Work one cable at a time if there are two or three entries. Keep track of which colour goes where — your photograph is the reference, not memory.

In modern wiring: brown is Line (L), blue is Neutral (N), green/yellow is Earth (E). In older wiring: red is Line, black is Neutral, bare copper or green is Earth. The bare earth must always receive a green/yellow sleeve before refitting.

5. Fit the new back box (if needed)

If you are fitting a deeper or wider box in solid plaster, chisel the recess to the new size with a cold chisel. A double back box is typically 147 mm wide by 87 mm tall. Fit the new box with screws into plugs or into the masonry, or use adhesive plaster to set it flush. Make good around the edge with filler before the faceplate goes on. On a surface-mount job, fix the pattress to the wall with two screws and feed the cables through the knockout hole.

6. Connect to the new double faceplate

A double gang socket has the same three terminals as a single — Line, Neutral and Earth — wired once to feed both outlets. Connect each conductor to its correct terminal: brown (or red) to L, blue (or black) to N, green/yellow to the earth terminal. Tighten each screw firmly until the conductor cannot be pulled free with a light tug. Avoid over-tightening on plastic-bodied faceplates.

If the back box is metal, a short earth tail (green/yellow sleeved, minimum 2.5 mm²) must run from the box earth terminal to the faceplate earth terminal. This is easy to forget and important.

7. Dress the cables and refit the plate

Fold the conductors carefully into the box so no insulation is pinched under the edge of the faceplate. Press the plate home and fit the two fixing screws evenly so the plate sits flush and square. Do not overtighten — the plastic bosses inside a plastic faceplate can crack.

8. Restore power and test

Back to the consumer unit — switch the circuit on. If the RCD or MCB trips immediately, switch off again and check your work. Usually a conductor has touched something it should not. If everything stays on, test both outlets with a socket tester (the type with three LEDs) or by plugging in a lamp. Both sockets should read correct polarity with no fault indication.

When to call us

A straightforward single-to-double upgrade on a modern ring is within reach for a careful homeowner. The moment you find the cables are old, there is no earth, or the box is in an awkward position near a water source, call a qualified electrician. Richard covers Sandwich, Deal, Dover and east Kent for small socket jobs at the £10 per 10-minute rate.