When do I need an RCD socket rather than a standard socket?

You need an RCD socket when the circuit feeding it has no 30 mA RCD protection upstream. This applies in older homes with Type A (pre-RCD) consumer units, garage sub-boards without RCD coverage, and any outdoor socket. From the 17th Edition (2008), BS 7671 has required 30 mA RCD protection for all 13A socket outlets in domestic premises — an RCD socket provides this locally when the board cannot.

What is the difference between an RCD socket and an RCBO?

An RCBO is fitted in the consumer unit and protects the entire circuit. An RCD socket protects only the socket it is fitted at, plus any sockets connected downstream on the Load (Out) terminals. For one or two sockets needing protection in an old installation, an RCD socket is simpler than changing the consumer unit breaker. For whole-circuit protection, an RCBO is the cleaner solution.

Do I need to press the Reset button before use?

Yes. All RCD sockets come in the tripped state from the factory. Before the socket will supply power you must press the Reset button on the face of the socket. If the socket does not supply power after wiring and energising, always check the Reset button first.

How to Fit an RCD Socket Outlet (UK)

Helpful video reference. We use Eastway Electrical's "Fitting RCD Sockets" as the video reference here. Eastway Electrical is a London-based electrical contracting firm and their video demonstrates the practical process of swapping standard sockets for RCD-protected ones in a real UK domestic installation, including the terminal connections and the built-in test procedure.

Before you start. Switch off the circuit at the consumer unit, not just at the socket switch. Confirm dead with a voltage tester on every outlet you plan to open. If the cables inside the back box are rubber-insulated or cloth-sheathed, or if there is no earth conductor present, stop and call an electrician before going any further.

1. Work out whether an RCD socket is actually what you need

First check whether the circuit already has RCD protection. Open the consumer unit cover (with the mains off) and look at the breaker for the circuit in question. If it is an RCBO, the circuit is already protected and a standard socket is fine. If the board has a master RCD covering a bank of MCBs, those circuits are also protected.

An RCD socket is the right choice when:

The circuit MCB is a plain MCB with no RCD coverage (common in older Type A boards from before 2008).
You are fitting a new outdoor socket where a dedicated RCD circuit from the board is not practical.
You are fitting a socket in a garage, workshop or outbuilding that runs off a plain MCB with no RCD.
You want added protection at a specific socket without changing the consumer unit.

In a fully modern board (post-2008, with RCBOs or a split-load arrangement), every socket circuit should already have 30 mA protection and an RCD socket adds nothing meaningful.

2. Buy the right socket for your back box depth

This is the step that catches most people out. A standard 13A socket can sit in a shallow 25 mm back box. Most RCD sockets are significantly deeper inside and need a minimum box depth of 35 mm. A few models need 47 mm. Measure your back box before you buy.

If the box is too shallow, you have two options: fit a surface-mount back box over the existing flush box (adds about 16 mm to the face), or replace the back box with a deeper one. Replacing the box in plasterboard is straightforward. In a solid masonry wall it means chipping out more depth, which is more involved.

Also check whether you want a single or double gang RCD socket. Double gang versions allow two outlets both protected by the single RCD mechanism. Single gang versions are common for outdoor use.

3. Isolate the circuit

At the consumer unit, switch off the MCB for the circuit. Confirm dead at the socket face with a voltage tester before unscrewing anything. Test both the live slot (the long slot on the left) and the neutral slot (long slot on the right). A neon screwdriver is not a reliable voltage tester. Use a two-pole or solenoid type.

4. Remove the existing socket and photograph the connections

Unscrew the faceplate, ease it out, and take a clear photo of the existing connections before you disconnect anything. On a standard single socket you will have live (brown), neutral (blue) and earth (green and yellow). If there are two sets of cables, the socket is mid-run in a ring or daisy chain and both cables need to transfer to the new terminals.

5. Connect the wires to the correct terminals

An RCD socket has two pairs of line and neutral terminals, marked differently depending on the manufacturer. The naming varies but the principle is consistent:

Line In / Neutral In (or Supply, or Unprotected): this is where the incoming cable from the consumer unit connects.
Line Out / Neutral Out (or Protected, or Load): this is where any outgoing cable to further sockets connects.

If there is only one cable, it connects to the In (Supply) terminals. Earth connects to the single earth terminal regardless of which set it comes from.

Getting the terminals swapped (putting supply on the Out terminals) means the RCD mechanism is not in the correct position in the circuit. The socket may appear to work but the RCD will not provide protection correctly. Check the instruction sheet that comes with the socket before connecting.

6. Press the Reset button before closing up

All RCD sockets are supplied in the tripped (open) state for safety. Before you fold the cables back into the box and screw the faceplate down, press the Reset button on the face. You will feel or hear it click in. If you do not reset it now, the socket will not supply power even after the circuit is energised and you will spend ten minutes wondering why.

Fold the cables gently back into the box without trapping any insulation under the plate edge. Tighten the two faceplate screws evenly.

7. Restore power and test thoroughly

Switch the MCB back on. Plug a plug-in socket tester into the new RCD socket. A healthy reading confirms correct polarity, live, neutral and earth connections. If it shows a fault, switch off and recheck the wiring.

Once the tester shows correct, press the T (Test) button on the socket face. The socket should go dead immediately. Remove the tester, press Reset, reinsert the tester and confirm it reads correctly again. This verifies the RCD mechanism is working.

Test both outlets if you fitted a double gang socket. On most double gang RCD sockets, the Test and Reset buttons operate both outlets simultaneously.

Stop and call an electrician if: the socket tester shows a fault after wiring (reversed polarity, missing earth), the RCD mechanism does not trip when you press the T button, the back box is clearly too shallow but you cannot replace it easily, there is no earth conductor in the box and no confirmed reason why, or the cables are old rubber or cloth insulation.

When to call us

Swapping a socket like-for-like is well within the scope of a careful homeowner. Where it steps over the line is when the existing installation has problems: missing earths, incorrect polarity in the existing socket, a shallow box in a solid wall, or old wiring that needs assessing. Call before the work gets complicated.

Need a socket swap or RCD upgrade in east Kent?

Richard carries RCD sockets and socket testers and can sort a like-for-like swap on a small local job at the £10 per 10-minute rate.

Contact Richard

How to fit an RCD socket outlet in a UK home