Single-Phase Socket Outlet Wiring
Ring finals vs radials, correct terminations, spurs, and the checks before you screw it back to the wall.
BS 7671:2018+A4:2026IET On-Site Guide
Socket circuits are the bread and butter of domestic work, and also where small mistakes: a loose cpc, a broken ring, an over-loaded spur: cause the most call-backs. This covers the two circuit types, how to terminate correctly, and the rules for spurs.
Ring final vs radial
| Circuit | Cable | Protective device | Notes |
|---|---|---|---|
| Common ring-final example | 2.5 mm² T&E | 32 A | Both ends return to one protective device; the complete Appendix 15 conditions and actual installation factors must be checked. |
| Common radial example | 2.5 mm² | 20 A | One outgoing path; current capacity, voltage drop, fault protection, grouping, insulation, and route govern suitability. |
| Larger radial example | 4 mm² | 32 A | Not a universal prescription; verify every design factor and accessory/device rating. |
A correctly designed ring final provides two conductor paths back to one protective device. An open conductor changes current sharing and can leave part of the circuit carrying more current than intended without operating a 32 A device. Ring continuity and conductor-relationship tests are therefore essential before energization and after relevant alterations.
Terminating a socket
1
Prepare the conductors
Strip only as much insulation as the terminal needs; no bare copper should show below the terminal. Sleeve every cpc in green/yellow: bare cpcs in a back box are a common fail.
2
Match by function, not colour habit
Brown line → L, blue neutral → N, green/yellow cpc → E. On a ring, two conductors go into each terminal: make sure both are captured and tight.
3
Torque the terminals
Tighten to the maker's figure. Under-tight terminals arc and overheat; over-tight can shear a stranded conductor. Give each conductor a gentle tug to confirm it's held.
4
Dress and fit
Fold conductors neatly into the box without trapping them behind the screws or the accessory. Check the earth tail to the box (metal boxes) is connected.
Protective continuity to metalwork
Exposed-conductive-parts require reliable protective continuity. For a metal back box, verify the approved connection arrangement, fixed-lug/contact path where applicable, accessory manufacturer instructions, and continuity. A separate protective fly-lead may be required or adopted by specification; do not infer continuity from fixing screws alone without verification.
Spurs: the rules people break
- Use the current BS 7671 Appendix 15 arrangements and the circuit design when adding a spur; do not treat a remembered socket count as the complete rule.
- A non-fused spur is limited by the connected accessory/load arrangement and conductor capacity. Confirm the point of connection and that the ring itself remains continuous and correctly loaded.
- A suitably selected fused connection unit can limit the downstream load and protect the downstream cable, but its fuse rating, cable size, accessibility, and isolation function still require design.
- Do not extend an unfused spur into an uncontrolled chain. Trace the existing circuit first because undocumented spurs, junctions, and broken rings are common alteration risks.
Before you sign it off
- Ring continuity: prove the ring is unbroken (the three-step r1/rn/r2 method).
- Insulation resistance: dead test, ≥ 1 MΩ.
- Polarity: line to the switched/fused terminal everywhere; no reversed L–N.
- Zs and RCD operation: confirm disconnection times and 30 mA additional protection.
Reference material for competent electrical work. Use the sources and jurisdiction stated in this guide, and always confirm the current rules, equipment instructions, and site conditions before relying on a value or procedure.