Every outdoor socket needs 30 mA RCD additional protection under BS 7671 Regulation 411.3.3, and it needs it at the socket or upstream, not on a plug-in adaptor that the customer can leave in the drawer. The rest of an outdoor socket job is about the environment: an enclosure that keeps water out with the plug in, a cable that survives sunlight and spades, and, on a PME supply, thought about whether the earth you export to the garden is one you want out there. This guide covers the regulations, the cable and enclosure choices, Part P, and what goes on the Minor Works Certificate or EIC.
- 30 mA RCD protection is mandatory for outdoor sockets (411.3.3); type A is the sensible minimum.
- Choose an IP66 enclosure that stays at least IP44 with a plug inserted, and mount it where hoses and sprinklers cannot reach.
- Twin and earth is for the through-wall run only; SWA or cable in suitable conduit for anything exposed or buried.
- On a TN-C-S supply consider whether the PME earth should be exported; for a socket on the house wall it normally is, for a socket at the far end of the garden think about TT.
- Test and record Zs, insulation resistance, polarity and the RCD trip times at the new outlet.
What does BS 7671 require for an outdoor socket?
The relevant regulations for a socket on the outside of a dwelling:
| Regulation | Requirement |
|---|---|
| 411.3.3 | Additional protection by 30 mA RCD for sockets up to 32 A and for mobile equipment used outdoors up to 32 A |
| 512.2 | Equipment selected to suit the external influences (water, UV, impact, temperature) |
| 522 | Cables selected and installed for the environment: UV (522.11), mechanical damage (522.6), water (522.3) |
| 522.8.10 | Buried cables: armoured, or in earthed metal conduit, or in ducting with mechanical protection, with route marking |
| 542, 544 | Earthing and bonding; for outbuildings and TT islands, an electrode to 542.2 |
| 411.4 | On TN-C-S, the risk from a broken PEN to a person outdoors in contact with earth |
| 553.1 | Socket outlets to BS 1363 or, for outdoor and commercial use, BS EN 60309 |
Note what is not required: there is no rule that an outdoor socket must be on its own circuit, must be switched, or must be at a particular height. Those are design choices.
Which RCD arrangement is right?
Three ways to meet 411.3.3:
- RCBO at the consumer unit protecting the whole circuit. Cleanest, protects the cable in the wall as well (522.6.202), and no extra device outside. Preferred on a board change or new circuit.
- RCD fused connection unit indoors feeding the outdoor socket as a spur. Good on an older non-RCD board where a spur is being taken from a ring final. Puts the test button where the customer can reach it in the dry.
- RCD-protected outdoor socket (a socket with an integral 30 mA RCD). Common and compliant, but the RCD lives in the wet, the test button is outdoors, and the cable from the board to the socket is unprotected if the circuit has no RCD.
Whichever is chosen, the residual current type matters. Garden equipment increasingly means battery chargers, pressure washers with electronic controls, pond pumps with inverters and EV charging leads plugged into a 13 A socket. Regulation 531.3.3 requires the RCD type to suit the load; type A is the sensible minimum, and an EV charging cable with a 13 A plug needs its own protective measures under Section 722 if it is to be used regularly. See RCBO vs RCD Split-Load Boards: Which to Fit and Why for the type A, F and B distinctions.
What enclosure and IP rating?
BS 7671 leaves the IP rating to the designer's assessment of external influences under 512.2 and Appendix 5, so the numbers below are industry practice rather than a regulation:
| Location | Suggested rating |
|---|---|
| On a house wall under an eave, plug in for short periods | IP44 minimum with plug inserted; IP66 lid closed |
| Exposed wall, near a hose or sprinkler | IP66 lid closed, IP55 or better in use |
| Freestanding post in a lawn or border | IP66, on a rated post with a cable gland below ground level |
| Inside a garage or outbuilding | Standard indoor accessories acceptable |
Look for BS 1363-2 sockets inside an enclosure tested to BS EN 60529 for the IP rating, with a hinged cover that closes over a plug and a lockable option where children or the public have access. Mount the socket high enough to clear standing water and splashing from paths, and low enough to reach without a lead trailing up the wall. A common failure on EICRs is an IP-rated enclosure with the cable entering through an unglanded hole at the top; water follows the cable in.
Which cable?
The through-wall run from an indoor spur or the board to a socket on the same wall is normally twin and earth in a sleeve or short length of conduit, with the hole sealed. Beyond that:
| Route | Cable |
|---|---|
| Along an external wall, exposed | SWA, or T&E in UV-resistant conduit; flat T&E clipped direct is not acceptable (522.11) |
| Along a fence or pergola | SWA; fences move and rot, so avoid if possible |
| Buried | SWA at a depth that avoids disturbance (commonly 500 mm minimum, with marker tape), in accordance with 522.8.10; or cable in ducting with warning tape |
| Overhead span | Catenary wire with cable supported, or SWA self-supporting for short spans |
| Feeding an outbuilding | SWA sized for the load and the length; see the outbuilding guide |
SWA glands need to be the correct type for the armour and the enclosure, and where the armour is used as the CPC (or as a parallel path) its continuity must be tested. A 2.5 mm² three-core SWA with the armour as CPC is normal for a garden socket radial; using the third core as CPC and earthing the armour at the supply end only is also common and avoids exporting a PME earth via the armour, but the design must be recorded. Outbuilding and Garden Supply: SWA, TT or PME Earth? goes into the armour-as-CPC question in more detail.
Should the PME earth be taken into the garden?
On a TN-C-S (PME) supply the installation's earth is the supply neutral. If the PEN breaks, the earth rises towards line voltage. Indoors, bonding keeps everything equal. Outdoors, someone holding a metal-cased hedge trimmer plugged into the socket, standing on wet grass, is between the raised earth and true earth. BS 7671 does not prohibit PME earths on outdoor sockets, and for a socket on the wall of the house it is universal practice. It does restrict PME for EV charging (722.411.4.1), caravans (708) and swimming pools and hot tubs (702), and it asks the designer to consider the risk (411.4).
Practical guidance most electricians follow:
- Socket on the house wall, normal garden use: PME earth, RCD protection, no further measures.
- Socket at the end of a long garden, on a post, or in an outbuilding with a lot of metalwork: consider a TT island with a rod, an RCD at the origin of the outdoor circuit, and no PME earth exported (the SWA armour earthed at the house end only or the cable in plastic conduit).
- Socket that will supply an EV charger or hot tub: follow Section 722 or 702; a 13 A socket is not the right answer for either. See EV Charger Installation Certificate: Section 722 and the EIC.
If the supply is TN-S or TT the PEN risk does not arise, but a TT installation's outdoor circuit still needs RCD protection and the electrode resistance still governs. Earthing Arrangements Explained: TN-S, TN-C-S and TT covers the identification.
Is it notifiable under Part P?
In England, since 6 April 2013 the notifiable list is: a new circuit, replacement of a consumer unit, and work in a special location (rooms containing a bath or shower, swimming pools, saunas). A garden socket spurred from an existing ring final is therefore not notifiable. A new radial from the board to the garden is. In Wales, the pre-2013 list still applies, which includes work outdoors, so most outdoor socket work is notifiable there. In either country, non-notifiable work still has to comply with BS 7671 and be certificated. See Part P notification: when and how electricians notify building work.
What do you test and certify?
For a spur from an existing circuit, a Minor Electrical Installation Works Certificate is the right document; for a new circuit, an EIC. Either way, the tests and results at the new outlet:
| Test | What to record |
|---|---|
| Continuity of CPC (R1+R2) and of SWA armour if used as CPC or parallel path | Ohms |
| Insulation resistance of the new cable | MΩ at 500 V |
| Polarity | Confirmed |
| Zs at the socket | Ohms, against the device maximum (and the RCD figure if the RCD provides fault protection) |
| RCD operation at IΔn and 5×IΔn, both half-cycles | ms; test button confirmed |
| Ze and earthing arrangement of the installation | Recorded on the certificate |
On a Minor Works Certificate the existing circuit's protective device, the earthing arrangement and whether the existing installation's earthing and bonding are adequate must be confirmed; a missing main bond found while adding a garden socket needs to be recorded and the client told, even though it is not part of the job. Minor Works Certificate: When to Use It (and When Not To) covers the boundary between Minor Works and EIC, and RCD Testing Explained: Types, Test Currents and Trip Times the trip-time sequence.
What do you look for on an EICR?
Outdoor sockets are a reliable source of observations. The usual findings and codes, following Best Practice Guide 4: no RCD protection, C2; twin and earth clipped along an external wall or fence, C2 where damaged or C3 where intact and out of reach; a socket enclosure with a broken lid or water inside, C2; SWA with the armour not earthed at either end, C2 where the armour could become live; a garden socket on a PME earth feeding a hot tub, C2 with reference to Section 702. A well-installed IP66 socket on an RCBO with SWA correctly glanded gets no observation at all, which is the aim.
How Certio helps
Certio produces the EICR, EIC, Minor Works certificate and PAT records on the BS 7671 model forms and turns them into branded PDFs. Photograph the consumer unit and the circuit schedule drafts itself; point the phone camera at a Megger MFT-X1 and the reading goes straight into the schedule of test results, or dictate it while your hands stay on the probes. Suggested observation wording with the regulation reference is there for you to check and confirm. The judgement stays yours; the typing goes. Starter is free for 7 days, then £5 a month.