How do I know if a socket is on the ring or already a spur?

Open the back box. A socket on the ring final circuit has two cables in it. A spur socket has one cable. You may only spur from a socket that has two cables (i.e. is on the ring itself).

Is adding a spur socket notifiable under Part P?

Adding a spur to an existing ring final circuit in a standard room is generally not notifiable under Part P Building Regulations in England. However, any new work in a kitchen, bathroom, outdoors or within 3 metres of a bath or shower zone is notifiable and must be carried out by a Part P registered electrician or notified to Building Control.

What cable do I need for a spur socket?

Use 2.5mm two-core-and-earth cable throughout, the same size as the ring itself. Do not use 1mm or 1.5mm for socket spurs — those sizes are only adequate for lighting circuits.

Can I have more than one socket on a spur?

A single fused spur (via a fused connection unit) can supply more than one socket, but an unfused spur from the ring is limited to one single or double socket outlet. If you need more sockets in that area, a fused spur to a local spur board is the correct approach.

How to Add a Spur Socket to a Ring Main (UK)

Helpful video reference. John Ward of Flameport Electrical, Poole, demonstrates extending a ring final circuit in his video "How to Add more Sockets to a ring Circuit". John is one of the most respected UK electrical educators online, and his explanation of the ring final circuit — what distinguishes a ring socket from a spur socket, and how to make the connection correctly — is well worth watching before you start.

Before you start. Turn the ring final circuit off at the consumer unit and confirm dead with an approved voltage tester at the donor socket. This is not optional. Also read step 1 carefully before touching anything: running a spur from a socket that is already a spur is a wiring defect that your MCB will not protect you from. Check the number of cables first.

1. Identify a suitable donor socket on the ring

The donor socket — the one you will take the spur from — must be on the ring itself, not on an existing spur. Open the back box and count the cables.

Two cables in the back box — the socket is on the ring. This is a valid donor.
One cable in the back box — the socket is already a spur. You cannot take another spur from here.

Under BS 7671, only one unfused spur is permitted per socket outlet on the ring. Connecting a spur to another spur creates a defect and can result in a socket that is inadequately protected against overload.

2. Plan the cable run

Use 2.5mm two-core-and-earth cable for the entire run from donor socket to new socket. Do not use 1.5mm or 1mm — those are lighting sizes. The cable must be clipped at regular intervals, run in conduit in solid walls, or otherwise mechanically protected throughout.

Where the cable runs through a wall, a short length of oval conduit is the neatest solution. Through timber-framed walls, drill through the studs and sleeve the cable where it passes through the plasterboard.

3. Isolate the circuit and confirm dead

Switch off the ring final circuit breaker at the consumer unit. Label the breaker so nobody switches it back on while you are working. Go to the donor socket and test every slot with an approved voltage tester. All should read zero. Now you can unscrew the faceplate and take a clear photo of the existing wiring before disconnecting anything.

4. Fix the new back box and run the cable

Fit the new back box in your chosen location. Chase out the wall, or clip the cable on the surface if you prefer a visible conduit run. Feed the cable into the donor socket back box and into the new back box, leaving enough length at each end to work comfortably — about 150mm of cable protruding from each box is right.

If you are chasing a solid wall, strip the cable sheathing back to the wall surface only. Leaving sheathed cable inside the chase reduces heat dissipation and is not best practice.

5. Wire the new socket

At the new socket end, the wiring is simple — only one cable. Strip the conductors, sleeving the bare earth with green and yellow sleeving:

Brown conductor to the L terminal
Blue conductor to the N terminal
Green/yellow earth to the E terminal

If the back box is metal, add a short earth fly lead from the E terminal on the faceplate to the earth screw on the box. Tighten all terminals firmly and refit the faceplate.

6. Connect the spur at the donor socket

At the donor socket, you will have three sets of conductors after this step: the two ring cables already there, plus the new spur cable. Each terminal will take three conductors.

Add the spur's brown conductor alongside the two existing browns at L
Add the spur's blue conductor alongside the two existing blues at N
Add the spur's earth alongside the existing earths at E

Tighten each terminal firmly. Three 2.5mm conductors in a standard socket terminal is tight but correct — check the socket manufacturer's instructions to confirm it is rated for this. If not, a suitable connector block inside the back box may be needed.

7. Restore power and test

Refit the donor socket faceplate and return to the consumer unit. Switch the circuit back on. Test both sockets with a plug-in socket tester: it will confirm correct polarity and the presence of an earth. A green light on both sockets means the job is done correctly.

Stop and call an electrician if: you find the donor socket has already been used as a spur (one cable in the back box); the cable insulation in the wall is rubber or cloth-braided; the MCB or RCD trips when you restore power; the socket tester shows incorrect polarity or a missing earth; or you realise you need more than one extra socket in that area (at which point a fused spur board or a dedicated radial is the right answer).

When to call us

A single spur in a standard room is a reasonable DIY job for someone who is comfortable working with electrical cables. If you need multiple sockets, if the work is in a kitchen, bathroom or outdoors, or if the existing wiring raises any doubt, that is a job for a registered electrician. In Sandwich and east Kent, Richard can add sockets cleanly on a small-jobs visit.

Need extra sockets in Sandwich?

Richard can add sockets, install fused spur boards and advise on the best approach for your layout. Small jobs at £10 per 10 minutes.

Contact Richard

How to add a spur socket to a ring main