Wiring a plug or wall socket is one of the most common DIY electrical tasks, and also one where small mistakes -- a crossed terminal, a loose screw -- have serious consequences. This guide covers the wiring of a 3-pin plug and a wall outlet/socket: the terminal assignments, wire colors, and fuse ratings for both the UK (BS 1363) and US (NEC) conventions, since the terminology "plug socket" covers different hardware depending on where you are.
UK 3-Pin Plug Wiring (BS 1363)
The UK uses one of the safest plug standards in the world. The BS 1363 plug has three large rectangular pins: a longer top pin (earth) and two shorter bottom pins (live and neutral). Every BS 1363 plug contains a fuse -- this is unique to the UK system and provides per-appliance overcurrent protection at the plug itself.
UK Wire Colors (Post-2004)
Since March 2004, UK and European harmonized wiring uses:
- Brown: Live (L)
- Blue: Neutral (N)
- Green/Yellow stripe: Earth (E or PE)
Older UK wiring (pre-2004) used red for live and black for neutral -- if you are working on old wiring, treat any red wire as live and any black wire as neutral.
UK 3-Pin Plug Terminal Assignments
[E -- top pin, longest]
/
/ [L -- bottom right pin]
\ [N -- bottom left pin]
\
Looking at the face of the plug with the earth pin at the top:
| Terminal | Wire Color | Pin Position |
|---|---|---|
| E (Earth) | Green/Yellow | Top (longest pin) |
| L (Live) | Brown | Bottom right |
| N (Neutral) | Blue | Bottom left |
Wiring a UK BS 1363 Plug -- Step-by-Step
Safety: Always disconnect from the mains before opening any plug or socket. Verify with a voltage tester.
- Unscrew the large central screw on the back of the plug to open it.
- Loosen the cable clamp screws at the bottom of the plug. The cable clamp must grip the outer insulation -- not the individual cores.
- Strip approximately 40 mm of outer sheath. Strip 8 mm of insulation from each core.
- Brown wire: Screw into the L terminal (bottom right). No loose strands.
- Blue wire: Screw into the N terminal (bottom left).
- Green/Yellow wire: Screw into the E terminal (top). The earth core should be slightly longer inside the plug so it is the last to disconnect if the cable is yanked.
- Check the fuse rating matches the appliance:
- 3A fuse (red): Appliances up to 700W (table lamps, phone chargers, shavers)
- 13A fuse (brown): Appliances 700W to 3000W (kettles, irons, vacuum cleaners, microwave ovens)
- Tighten the cable clamp firmly on the outer sheath.
- Close the plug and tighten the central screw.
UK Wall Socket Wiring
A UK 13A double socket (BS 1363) has the same terminal labels:
- L: Live -- brown or red (old)
- N: Neutral -- blue or black (old)
- E: Earth -- green/yellow
At the socket, the cable entry is from behind via a metal box (single gang, double gang). Standard single sockets serve one outlet; double sockets serve two. Each socket has its own L, N, and E terminals, though a ring main feeds both from a single cable loop.
Ring main wiring: In a UK ring circuit, two cables arrive at each socket -- one from the previous socket, one continuing to the next. Both live wires connect to the L terminal (using a connector block or by doubling under the same terminal screw), both neutrals to N, and both earths to E. The outer sheath of each cable must be identified with its cable number for future reference.
US 3-Prong Outlet Wiring (NEC)
The US uses NEMA 5-15 (15A, 120V) and NEMA 5-20 (20A, 120V) receptacles for standard residential and commercial outlets. Unlike UK plugs, US outlets do not contain a fuse -- overcurrent protection is at the circuit breaker in the panel.
US Wire Colors (NEC)
- Black: Hot (ungrounded conductor)
- White: Neutral (grounded conductor)
- Bare copper or green: Equipment grounding conductor (EGC)
On 240V circuits: black is one hot, red is the second hot, white is neutral, green/bare is ground.
US Outlet Terminal Assignments
A standard duplex NEMA 5-15R receptacle has:
| Terminal | Color | Wire |
|---|---|---|
| Brass (gold) screws | Black | Hot |
| Silver screws | White | Neutral |
| Green screw | Green/Bare | Ground |
The narrow slot (hot) is on the right side of each outlet face. The wide slot (neutral) is on the left. The round hole at the bottom is the ground.
Wiring a US Duplex Outlet -- Step-by-Step
Safety: Turn off the circuit breaker and verify the outlet is dead with a non-contact voltage tester before touching any wires.
- Strip approximately 3/4 inch (19 mm) of insulation from each conductor.
- Black wire: Wrap clockwise under the brass (hot) screw. Tighten firmly.
- White wire: Wrap clockwise under the silver (neutral) screw. Tighten firmly.
- Bare or green wire: Connect to the green screw (ground).
- If the outlet has a break-off tab between the two brass screws (split-circuit outlet), verify whether it needs to stay intact or be removed for your application. A standard outlet keeps the tab in place -- both outlets share the same hot and neutral.
- Fold the wires carefully into the box. Push the outlet into the box and secure with the two mounting screws.
- Install the cover plate.
- Restore power and verify with a plug-in outlet tester (a 3-light tester is adequate).
GFCI Outlets
GFCI (Ground Fault Circuit Interrupter) outlets are required by NEC 210.8 in wet or damp locations: kitchens within 6 feet of a sink, bathrooms, garages, outdoors, crawl spaces, unfinished basements, and near pools. A GFCI outlet has LINE and LOAD terminals:
- LINE: The incoming hot and neutral from the panel.
- LOAD: Connects to any downstream outlets that the GFCI protects.
Wire colors are the same -- black to hot (LINE), white to neutral (LINE), ground to green. Do not reverse LINE and LOAD -- the GFCI will not function correctly.
Common Mistakes in Plug and Socket Wiring
- Reversed live and neutral (UK): The plug will work for many appliances, but the appliance body may be at live potential when the switch is off.
- Live and neutral reversed at a US outlet: Polarized plugs (where one prong is wider) will not fit, and table lamp sockets will have a live shell instead of a live center contact.
- Loose cable clamp (UK plug): The cable can pull out of the plug, leaving the earth disconnected first and exposing live terminals.
- Strand bridges (both systems): A stray strand of copper touching an adjacent terminal causes a short circuit or shock hazard.
- Wrong fuse rating (UK): A 13A fuse in a lamp plug provides essentially no protection for a 60W lamp's wiring.
- No ground connection: Connecting only hot and neutral and leaving the ground unconnected means the appliance frame is unprotected in a fault.
Create Your Own Plug and Socket Wiring Diagram
Whether you are documenting a custom installation or teaching wiring conventions, having a clear diagram prevents terminal confusion. With CircuitDiagramMaker, you can:
- Draw both UK BS 1363 and US NEMA outlet pinouts with correct terminal labels
- Show wire color coding for both pre- and post-2004 UK conventions
- Illustrate ring main and radial circuit connections for UK sockets
- Add safety notes and fuse ratings directly to the diagram
- Export a reference diagram for installation or training documentation
Create your own plug and socket wiring diagram -- free
Key Takeaways
- UK BS 1363 plugs: brown = live (L), blue = neutral (N), green/yellow = earth (E). Earth pin is the longest and connects top.
- Every UK BS 1363 plug contains a fuse -- 3A for appliances under 700W, 13A for up to 3000W.
- US NEMA outlets: black = hot (brass screws), white = neutral (silver screws), bare/green = ground (green screw). Hot is always the narrow slot.
- Neither live/neutral nor hot/neutral should be reversed -- polarity matters for safety even in resistive loads.
- The cable clamp in a UK plug must grip the outer sheath, not the individual cores.
- US outlets in wet/damp locations must be GFCI protected per NEC 210.8.
- Always verify dead with a voltage tester before opening any outlet or plug.
Originally published at https://circuitdiagrammaker.app/blog/plug-socket-wiring-diagram.
