Few household jobs are as quick, or as easy to get wrong, as wiring a 13-amp plug. Do it properly and it will quietly outlast the appliance it serves. Do it badly and you end up with something that runs warm, blows fuses, or gives the next person to pick it up a shock. The good news is that a British three-pin plug is a forgiving piece of design: the fuse sits in the live conductor, the cord grip takes the strain off the terminals, and everything is reachable with one screwdriver. Get the stripping and the terminations right and there is very little left to go wrong.

Before you start: tools, plug and fuse

Everything you need fits in a shirt pocket, but the right versions matter. A plug that complies with BS 1363, with sleeved live and neutral pins, is the standard item sold in every DIY shop. Check the body for cracks before you start. A cracked plug goes in the bin, no debate.

• A small flat-blade screwdriver that genuinely fits the terminal screws. Too big or worn, and you will chew the screw heads and round them off.
• Wire strippers, or a sharp knife and a steady hand. Side cutters alone tend to nick the copper, which weakens the core exactly where the flex bends.
• A BS 1362 cartridge fuse of the right rating. 3A suits lamps and small appliances up to roughly 700W. 13A suits kettles, heaters and irons. If the manufacturer's instructions specify a rating, follow them.
• Good light, and somewhere safe to put the cover screw where you will find it again.

Fuse ratings are not a place to improvise. The fuse protects the flex as well as the appliance, so fitting a bigger fuse because the 3A one keeps blowing is how cables overheat. Match the fuse to the load, not to your patience.

Unplug the appliance before you touch anything. If the flex runs from a spur or a fixed connection rather than a plug, isolate the circuit at the consumer unit and confirm it is dead before you start. Nobody should be working on a live conductor for a job like this.

Live, neutral and earth: knowing which core is which

Modern flex uses harmonised colours, and there are only three to learn.

• Brown — live, which goes to the terminal marked L.
• Blue — neutral, which goes to N.
• Green and yellow — earth, which goes to E, usually marked with the earth symbol.

Older flex, and anything still lurking in a drawer from the 1990s, may use the old colours: red for live, black for neutral, and plain green for earth. If the colours are faded, or the flex has clearly been repaired before with tape, replace the flex rather than guessing.

Some double-insulated appliances are supplied with two-core flex and no earth at all. That is normal, and the earth terminal is simply left empty. Never link the earth terminal to the neutral to "make it work".

Opening the plug and stripping the flex

Open it up

Undo the single screw in the centre of the cover and lift it off. The three terminals are now visible, along with the fuse. Keep the cover screw somewhere safe. A plug refitted without its screw is a plug that will eventually come apart in your hand.

Strip the sheath, not the copper

Cut the end of the flex square with side cutters, then remove the outer sheath. A sensible length is around 30 to 40mm, but the reliable method is to hold the flex against the plug: the sheath needs to reach the cord grip, and the cores need to reach their terminals with a little slack and no more.

Strip about 6 to 8mm of insulation from each core. Use strippers set to the right size. If you use a knife, score lightly round the insulation and pull it away, working away from your fingers and never cutting through to the copper. A ring of nicked strands under the insulation is where a flex breaks six months later.

Twist each bunch of strands gently in the direction they already lie. Leave the earth core a few millimetres longer than the live and neutral, so that if the cord grip ever fails, the earth is the last connection to be pulled out.

Do not tin the ends with solder, and do not fold the strands back on themselves to make the core look thicker. Both are old habits that produce a poor, unreliable connection under a screw.

Terminating each core

Hold the plug with the earth pin uppermost. The earth terminal is at the top, next to the earth pin. Most plugs have the letters L and N moulded into the plastic beside the other two terminals, and they are there for exactly this reason. If yours does not, follow the fuse: the live terminal is the one connected through it.

1. Screw the green and yellow core into the earth terminal first. It sits at the top, and getting it out of the way makes the other two easier to reach.
2. Take the brown core to L, the terminal wired through the fuse. Route it tidily, without crossing over the other cores.
3. Take the blue core to N.
4. Check every termination: all the strands inside the terminal, no whiskers straying towards a neighbouring terminal, no insulation trapped under the screw, and no bare copper poking out beyond the clamp. A single stray strand can bridge live and neutral, or live and earth, and that is a short circuit at best.
5. Tighten each screw firmly. Firm is enough. Plastic threads strip easily, and a stripped terminal will not hold.

Fuse, cord grip and closing up

Fit the correct fuse into its clips and check it seats properly at both ends. Then bring the cord grip into play. The clamp must close on the outer sheath, not on the individual cores. Tighten it, then give the flex a firm tug and a gentle twist. It should not slide or rotate. If it does, the grip is clamping the cores instead of the sheath, and the terminals are taking the strain. That is exactly the wrong way round.

Refit the cover, start the screw by hand so you do not cross-thread it, and tighten it down. Before you do, look at the terminals one last time from the side. Nothing should be touching anything it should not be.

Testing it, and knowing when to stop

Plug it in and switch on. If the appliance runs, the job is almost certainly fine. If the fuse blows straight away, unplug it and look for a fault: a stray strand, a core in the wrong terminal, or a fault inside the appliance itself. Do not answer a blowing fuse with a bigger one.

After a few minutes of use, feel the plug. A little warmth from the appliance is normal. A plug or flex that becomes noticeably hot, smells, or shows discoloured plastic needs attention immediately. Check the flex regularly for cuts, and replace any plug whose body is cracked or whose pins are bent.

Wiring a plug is not notifiable building work, and plenty of people do it perfectly well at the kitchen table. Fixed wiring is a different matter: sockets, circuits and consumer units fall under the building regulations and, in most cases, should be left to a registered electrician. So if a fuse keeps blowing, if you find scorched or damaged wiring, or if anything about the job feels uncertain, stop and call someone qualified. A plug is a small, inexpensive part. The consequences of getting it wrong are not.

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