When you buy an electrical appliance in the UK, it should come with a plug already fitted - either directly connected to the appliance, or as a power lead which just needs plugging in. However, you may have an appliance at home which you haven't used for a while - and hasn't got a plug attached.

The Basics of Wiring

Before trying to fit a plug, it is worth understanding a little of the design of a British plug, and the flex that will be connected to it.

You should also note that the official voltage for mains electricity in the UK is 230V, although it is often referred to as 240V. This brought the UK into line with the rest of Europe, which uses 230V electricity¹. However, there is a tolerance range which power companies may operate within, so many have chosen to continue to supply 240V electricity.

The Flex

A length of flex will usually consist of three insulated conductors², encased in an insulating sheath. Each of the conductors will have a different colour insulation, according to the terminal it should be connected to:

• Brown - Live
• Blue - Neutral
• Yellow and green - Earth

If you have any old style appliances, they may well have different colours:

• Red - Live
• Black - Neutral
• Green - Earth

This colour scheme was changed because people suffering from red-green colour blindness³ could not distinguish between the Live and Earth wires, with disastrous consequences.

Note that appliances which are double-insulated may not have an Earth wire, and some appliances (such as doorbells or fairy lights) may have flex consisting of two uncoloured wires.

The Plug

A standard plug consists of a plastic casing, with three 'pins' protruding, which make the electrical connection. There will also be a screw which can be undone, allowing the plug to be taken apart.

When buying a new plug, you should ensure that the Live and Neutral pins are part insulated - the shanks should be plastic (usually black), with only the tip of the pins exposed metal. This will reduce the risk of touching a 'live' circuit when inserting or removing the plug.

Inside the plug will be three connectors to connect the flex to, two clips for holding a fuse⁴ and a flex clamp. The connectors will be one of two types: post connectors, and clamp connectors.

Post connectors have a small hole in the side, near the top, and a screw on top. They can usually be pushed completely out of the plug. Clamp connectors have a screw top which is used to clamp the wire in place.

The connectors should also be marked - they may have the words Live, Neutral and Earth (or just the letters L, N and E) or have brown, blue and green coloured markings. You may also see a symbol used for Earth.

Fitting the Plug

Ensure that your appliance is in no way connected to the mains electricity and unscrew the plug. Remove the fuse (if one is fitted) by pulling it out from the clips.

Take the flex, hold the end next to the Earth terminal of the plug, and follow the path to the outlet of the plug. Mark the point on the flex just before it would pass through the flex clamp and remove the flex from the plug. Using a sharp knife, carefully remove the outer sheath from this portion of the flex. One technique is to cut along the flex, alowing you to open it out. The excess sheath can then be cut off. Be careful not to cut through the insulation of any of the individual wires!

You now need to measure the individual wires. Position the flex in the plug, with the sheathed section just being held by the flex clamp. Each wire should be long enough to connect firmly to the connector, but not so long as to require folding back on itself when the case is put back on the plug. Note that each wire must follow the sunken path within the plug. Cut each wire at the appropriate point.

The next step is to strip a little insulation off the end of each wire. It is recommended that you use wire strippers for this, although you can do it with a sharp knife. You should remove no more than 1cm of insulation from each wire. When you have stripped a wire, carefully twist the strands of copper wire together.

Now we are ready to start connecting the flex. Position the flex in the flex clamp, so that the sheathed section is just held by the clamp⁵. You may just have to push the flex into the clamp, or unscrew the clamp, place the wire in, and replace the clamp.

Taking each wire in turn, connect it to the correct connector (see above). If the plug has post connectors, fold the exposed copper wire in half, to give a double thickness. Loosen the screw in the connector, insert the wire, and tighten the screw. If the plug has clamp connectors, unscrew the top of the connector, bend the copper wire into a hook, and wrap it around the exposed terminal. Replace the top and tighten, being careful not to clamp the plastic insulation.

If the flex clamp is a screw type, tighten the screws, making sure that the portion of flex held has the outer sheath on it. None of the coloured wires should be visible outside the clamp.

You now need to check what kind of fuse your appliance requires. Every electrical appliance sold in the UK should have a label on it showing its power rating. Some will also give the current rating - so you don't need to do this calculation at all⁶.

There are two numbers you need to know - the voltage (230V⁷) and the maximum power usage (in Watts). Divide the maximum wattage by the voltage, and you will have the Amperage.

For example, a kettle may use 2,200 Watts, running on 230V mains electricity. 2,200 ÷ 230 = 9.6.

The fuse you need will be the next highest rating - in our example, 13 Amps. If you attempt to use a lower rated fuse, it will blow. However, you should certainly not use a 13A fuse for everything - doing so would not provide the correct protection. The most common fuses are 3A (red), 5A (black) and 13A (brown), although others may be available.

Carefully snap the fuse into the two fuse clips of the plug.

Make sure all your connections are secure and that the cover will not crush any of the wires, then replace the cover and tighten the screw.

Congratulations! You have just fitted a plug!