How to Wire a Plug: UK and US Guide
Wiring a plug is one of the few pieces of electrical work most people can do safely at home, but the details are not universal. A UK BS 1363 plug and a US NEMA 5-15 plug use different wire colors, different pin layouts, and one of them has a fuse built into the plug body while the other does not. Mixing up the two systems -- for example wiring a UK plug with US color assumptions -- is how appliances end up with live and neutral reversed.
This guide covers both regions in full. If you are in the United Kingdom (or anywhere else that uses the BS 1363 three-pin plug -- Ireland, and various Commonwealth and Gulf countries use compatible or near-identical standards), read the UK sections. If you are in the United States wiring a NEMA 5-15 replacement plug, skip to the US sections. Each section is clearly labeled so you can jump straight to the one that matches your plug.
Which Plug Do You Have: UK or US?
Before you start, confirm which standard you are working with. A UK BS 1363 plug is rectangular, has three flat rectangular pins in a triangular arrangement, and -- critically -- has a small fuse holder built into the plug body near the base of the live pin. A US NEMA 5-15 plug is smaller, has two flat parallel blade pins plus a round ground pin below them, and has no fuse holder anywhere in the plug.
If your plug does not match either description -- a European Schuko plug or an Australian AS/NZS plug, for example -- the "UK" color codes below (brown/blue/green-yellow) usually still apply, since most of the world uses the same IEC wire color standard, but the pin layout and fuse arrangement will differ. This guide only covers BS 1363 and NEMA 5-15 in detail.
UK BS 1363 Plug: Wire Colors and Pin Layout
UK flex (cable) uses three standard wire colors:
- Brown = live (L) -- carries current from the supply.
- Blue = neutral (N) -- carries current back to the supply.
- Green-and-yellow = earth (E) -- a safety conductor that carries fault current to ground if something goes wrong.
Hold the plug with the cord entering at the bottom and look at the back of the plug, where the terminals are. The three pins are arranged as follows:
- Earth pin -- top center. This is the largest of the three pins, and it is longer than the other two so it makes contact first when you insert the plug into a socket.
- Live pin -- bottom right.
- Neutral pin -- bottom left.
This layout is fixed by the BS 1363 standard, so every compliant plug and socket uses the same arrangement. The earth pin being both the largest and the longest is a deliberate safety feature -- it connects before the live and neutral pins make contact, and it disconnects last when you pull the plug out.
UK BS 1363 Plug: The Fuse and How to Choose the Right Rating
A feature unique to the UK system (and a few other countries that adopted BS 1363) is that the fuse sits inside the plug itself, in a small cartridge fuse holder built into the live pin. This is different from the US system, where NEMA plugs have no fuse at all and the branch circuit breaker in the consumer unit or panel is the only overcurrent protection.
The logic behind the plug fuse is that it should protect the flexible cable (the flex) running from the plug to the appliance, not just the appliance itself. UK ring main circuits are typically protected by a 30A or 32A breaker at the panel, far too high a rating to protect a thin appliance flex if a fault occurs. The plug fuse fills that gap by matching the rating closely to the appliance's actual running current.
Work out the right fuse using the standard power formula, P = IV (power = current times voltage). Rearranged, current I = P / V. On UK mains at 230V, a 700W appliance draws roughly 700 / 230 = 3.04A, and a 3000W appliance draws roughly 3000 / 230 = 13.04A. UK plug fuses are only commonly available in two standard household ratings -- 3A and 13A -- so you round up to whichever one comfortably covers the appliance's running current without being oversized.
| Appliance wattage | Typical appliances | Fuse rating |
|---|---|---|
| Up to about 700W | Lamps, phone and laptop chargers, radios, small electronics, string lights | 3A |
| About 700W to 3000W | Kettles, toasters, irons, space heaters, vacuum cleaners, hair dryers | 13A |
If you are not sure of an appliance's wattage, check the rating plate or label on the appliance itself -- it is usually printed near the power cord entry or on the base. When in doubt between the two ratings, use the 13A fuse only if the wattage genuinely calls for it; fitting an oversized fuse on a low-power appliance means the fuse will not blow quickly enough if the flex itself develops a fault, since the fuse is sized to protect the cable, not just to keep the appliance running.
UK BS 1363 Plug: Step-by-Step Wiring
Tools needed: a small flathead or Phillips screwdriver (check which your plug uses), wire strippers, side cutters.
- Unplug the appliance and make sure the cord is not connected to any power source before you begin.
- Unscrew and remove the plug's cover, usually held by a single large screw or two smaller screws.
- Loosen the cord grip (the clamp that holds the outer cable sheath) and slide the cable in far enough that each of the three inner cores can reach its terminal with a little slack -- do not pull it tight, since a taut wire strains the terminal screws over time.
- Strip back the outer sheath to expose the three inner cores (brown, blue, green-and-yellow), leaving enough sheathed cable inside the plug for the cord grip to clamp onto later.
- Strip roughly 10 to 12mm of insulation from each individual core -- enough for the bare wire to seat fully in its terminal with no bare copper left exposed once tightened.
- For screw-post terminals, twist the strands of each core tightly and loop the bare end clockwise around the post, or push it fully into the terminal hole for shuttered terminals.
- Connect the brown (live) core to the live terminal at the bottom right pin.
- Connect the blue (neutral) core to the neutral terminal at the bottom left pin.
- Connect the green-and-yellow (earth) core to the earth terminal at the top center pin.
- Tighten each terminal screw firmly, then gently tug each wire to confirm it is held securely.
- Fit the correct fuse (3A or 13A, per the table above) into the fuse holder in the live pin.
- Position the cable so the cord grip clamps the outer sheath only, never the bare conductors, so pulling strain never reaches the terminal screws.
- Tighten the cord grip screws.
- Replace the plug cover and its screw(s).
- Check that no bare wire is visible outside any terminal, and that the cover sits flush, before use.
US NEMA 5-15 Plug: Wire Colors, Screw Colors, and Polarity
US NEMA 5-15 plugs are used on standard 120V household appliances and extension cords. Cable typically uses these colors:
- Black = hot -- carries current from the outlet.
- White = neutral -- carries current back to the outlet.
- Green (or bare copper) = ground -- a safety conductor.
Replacement and molded plugs identify their terminals by screw color rather than pin position:
- Brass or gold screw = hot terminal -- connects to the black wire.
- Silver screw = neutral terminal -- connects to the white wire.
- Green screw = ground terminal -- connects to the green or bare wire.
NEMA 5-15 plugs are polarized: the neutral blade is wider than the hot blade, and the outlet's slots are sized to match. This means the plug can only be inserted one way, which keeps hot and neutral consistently oriented inside the appliance. Getting the wiring backward at the plug defeats this protection even though the plug will still physically fit the outlet, since a miswired plug simply reverses which blade carries which conductor.
Unlike UK plugs, NEMA 5-15 plugs have no user-replaceable fuse. Overcurrent protection for the branch circuit comes entirely from the circuit breaker in the panel, which is sized for the wiring in the wall, not for any individual appliance cord.
US NEMA 5-15 Plug: Step-by-Step Wiring
Tools needed: a small Phillips or flathead screwdriver, wire strippers, side cutters.
- Unplug the cord from any outlet and confirm the appliance is not connected to power before you start.
- If replacing an existing plug, cut the damaged plug off the cord, leaving as much cord length as possible.
- Unscrew and open the new plug body, or remove the cover on a quick-connect style plug.
- Strip about 3/4 inch (roughly 19mm) of outer jacket if the cord is not already jacket-stripped, exposing the black, white, and green (or bare) conductors.
- Strip roughly 5/8 inch (about 15mm) of insulation from each individual conductor.
- Feed the cord through the plug's strain-relief opening before connecting any wires.
- Twist the strands of each conductor tight, then hook or loop each one clockwise so tightening the screw draws the wire in.
- Connect the black (hot) wire to the brass or gold screw.
- Connect the white (neutral) wire to the silver screw.
- Connect the green (or bare copper) wire to the green screw.
- Tighten every terminal screw firmly and tug each wire gently to confirm it is secure.
- Tighten the strain-relief clamp onto the outer jacket, not onto the bare conductors, so the terminals bear no pulling force.
- Reassemble the plug body and its cover screws.
- Confirm no bare copper is visible outside any terminal before plugging the cord in.
Testing Your Work: Polarity and Earth/Ground Checks
After wiring either type of plug, test it before relying on it.
Plug-in socket tester (recommended for both regions): insert the finished plug into a plug-in outlet tester -- a small device with indicator lights that plugs directly into a socket. Its lights indicate a correctly wired plug, a reversed live/neutral (or hot/neutral), or a missing earth/ground. These testers are inexpensive and the fastest way to confirm your work.
Multimeter continuity check (works with no power connected): with the plug assembled and disconnected from any power source, set a multimeter to continuity or resistance mode.
- Touch one probe to the live/hot pin and the other to the live/hot terminal to confirm continuity only on that path.
- Repeat for neutral, confirming the neutral pin connects only to the neutral wire.
- Repeat for earth/ground, confirming that pin connects only to the green-and-yellow (UK) or green/bare (US) wire.
- Confirm there is no continuity between live/hot and neutral, or between either and earth/ground -- unexpected continuity suggests a short or a stray strand bridging two terminals.
This confirms correct polarity and a solid earth/ground path, which a visual check alone cannot guarantee.
UK vs US Wire and Terminal Reference Table
| Conductor function | UK wire color | UK pin position | US wire color | US terminal screw |
|---|---|---|---|---|
| Live / Hot | Brown | Bottom right | Black | Brass or gold |
| Neutral | Blue | Bottom left | White | Silver |
| Earth / Ground | Green-and-yellow | Top center (largest pin) | Green or bare copper | Green |
Safety Warnings
- Never wire a plug with the appliance connected to power. Unplug the cord from the wall before you open the plug body or touch any conductor.
- Check the cord for damage before rewiring. A cracked, nicked, or brittle outer sheath means the cable itself may need replacing, not just the plug.
- Do not bypass the earth or ground conductor. Skipping it removes the fault path that protects you if the appliance develops an internal short to its casing.
- Do not fit a UK fuse rating higher than the appliance needs. An oversized fuse will not react quickly enough to a developing fault in the flex.
- On metal-cased appliances, confirm the earth/ground wire is intact all the way through, not just at the plug -- a broken internal ground wire is invisible from outside the plug.
Common Mistakes
- Reversing live/hot and neutral. The single most common wiring error in both regions. Double-check terminal position (UK) or screw color (US) before tightening any screw, not after.
- Letting the cord grip or strain relief clamp the bare wires instead of the outer sheath. If the conductors take the mechanical strain, the terminal connections loosen over time and can eventually arc.
- Stripping too much insulation off individual conductors, leaving bare copper exposed where it can touch an adjacent terminal or the plug casing.
- Fitting the wrong UK fuse rating -- guessing without checking the appliance's actual wattage, or reusing whatever fuse was in a drawer.
- Leaving strands of wire loose or frayed at a terminal, which can work free and bridge two terminals together.
- Assuming a cord is dead because the appliance is switched off. Many appliance switches interrupt only one conductor; treat the whole cord as live until it is unplugged and tested.
Troubleshooting
| Symptom | Likely Cause | Fix |
|---|---|---|
| Appliance does not power on | Loose or missing connection at one terminal, most often live/hot or neutral | Open the plug, confirm each wire is fully seated and tight, and recheck with a continuity test |
| Fuse blows immediately after rewiring (UK) | Live and neutral, or live and earth, are crossed, or a strand of wire bridges two terminals | Turn off power, open the plug, verify brown is on the live pin and blue on neutral with no stray strands, then refit a correctly rated fuse |
| Socket tester shows reversed polarity | Live/hot and neutral wires are connected to the wrong terminals | Open the plug, swap the two conductors onto their correct terminals, and retest before use |
| Plug feels warm or loose during use | A terminal screw is undertightened, or the cord grip is not clamping the sheath, so the connection is making poor contact under load | Turn off power, retighten every terminal, and confirm the cord grip clamps the outer sheath, not the bare wires |
| Socket tester shows no earth/ground continuity | Earth or ground wire is disconnected, on the wrong terminal, or broken inside the cord | Check the earth/ground terminal first; if it is correctly wired at the plug, the fault is further up the cord and the cable should be replaced |
| Appliance trips the breaker instead of blowing the plug fuse (UK) | The 13A fuse did not clear the fault before the breaker did, often from a direct short rather than an overload | Do not simply reset the breaker and keep using the appliance -- inspect the flex and appliance for a short first |
Key Takeaways
- UK BS 1363 plugs use brown (live), blue (neutral), and green-and-yellow (earth), with the earth pin at top center, live bottom right, neutral bottom left.
- UK plugs house their own fuse in the live pin -- use 3A for appliances up to about 700W and 13A for appliances from about 700W up to 3000W.
- US NEMA 5-15 plugs use black (hot), white (neutral), and green or bare copper (ground), wired to brass/gold, silver, and green screws respectively.
- NEMA 5-15 plugs are polarized with a wider neutral blade so they can only be inserted one way -- there is no fuse in the plug itself, only the branch circuit breaker.
- Strip individual UK conductors to roughly 10-12mm, and always let the cord grip or strain relief clamp the outer sheath, never the bare wires.
- Test every finished plug with a socket tester or multimeter continuity check before relying on it, confirming correct polarity and a solid earth/ground path.
- Never wire a plug while it is connected to power, never skip the earth/ground conductor, and check the cord for damage before you start.
Frequently asked questions
What fuse should I use in a UK plug for a kettle?
Kettles typically draw between 2000W and 3000W, which works out to roughly 8.7A to 13A on 230V mains. That falls within the 13A fuse range, so fit a 13A fuse rather than the 3A fuse used for low-power devices like lamps or chargers.
Which wire goes on which screw in a US plug?
Connect the black (hot) wire to the brass or gold screw, the white (neutral) wire to the silver screw, and the green or bare copper (ground) wire to the green screw. This color-coded screw system is standard on nearly all US replacement and molded plugs.
Which pin is earth on a UK three-pin plug?
The earth pin is the top center pin when you hold the plug with the cord entering at the bottom. It is also the largest and longest of the three pins, so it makes contact first and disconnects last as a built-in safety feature of the BS 1363 standard.
Why can a NEMA 5-15 plug only be inserted one way?
NEMA 5-15 plugs are polarized: the neutral blade is wider than the hot blade, matching correspondingly sized slots on the outlet. This physically prevents the plug from being inserted backward, keeping hot and neutral consistently oriented inside the connected appliance.
Why does a UK plug fuse blow immediately after rewiring?
An immediate blown fuse after rewiring almost always means live and neutral, or live and earth, are crossed at the terminals, or a stray strand of wire is bridging two terminals. Turn off power, reopen the plug, and check each connection before fitting a fresh fuse.
Do US replacement plugs have a fuse inside them?
No. NEMA 5-15 plugs have no user-replaceable fuse of any kind. Overcurrent protection comes entirely from the branch circuit breaker in the electrical panel, which is sized to protect the building wiring rather than any individual appliance cord. If an appliance needs finer protection, it is built into the appliance itself.
Interactive diagrams for this guide
- Wiring A 3 Pin Plug
- 3 Pin Plug Wiring Diagram
- Diagram Of A Plug
- 3 Pin Plug Socket Wiring Diagram
- Three Pin Plug Diagram
- 3 Prong Plug Wiring Diagram
- Three Prong Plug Wiring Diagram
- 2 Prong Plug Wiring Diagram
- Plug Wire Diagram
- Extension Cord Plug Wiring Diagram