Wiring a UK Plug Correctly and Safely - A Pictorial Guide
British BS1363 Standard Plug
The BS1363 standard 3-pin plug is used in the UK, Ireland, Malayasia, Saudi Arabia and several other countries. The plug incorporates several safety features including a fuse to protect the power cord and equipment, and also shrouded pins to prevent inadvertent finger contact with the live or neutral pins during insertion and removal. By law in the EU, new appliances must be fitted with a non re-wireable plug, however occasionally you may need to fit a plug to an older appliance.
This guide shows you how to specifically wire a UK plug to a domestic appliance. However the same basic principles of wiring a BS1363 plug can be applied to wiring plugs from other countries, the main difference being that the colour coding of wiring is different.
If you don't feel confident about doing this, then don't do it!!! If you get the wire colours mixed up, and connect them to the wrong terminals, it can cause power to shut off, or worse still, electrocute you or someone else using an appliance
Wiring Colours in the EU
The Safest Plug in the World?
The BS1363 Plug is undoubtedly the safest plug in the world and has the following features:
- Fused The function of the fuse is to protect the power cord/flex from overheating and possibly catching fire. In a short circuit situation, a distribution circuit will supply current greater than a power cord/flex is capable of carrying (possibly tens of thousands of amps). The fuse in the plug will blow to protect the cord and may also protect wiring/components within an appliance. A fuse will also blow when more moderate overloads occur (e.g. attempting to power too many appliances from an extension reel)
- Insulated Pins This protects inadvertent contact with live pins during insertion and removal of the plug
- Shuttered Outlets on Sockets This prevents children from inserting pins, nails or other metal items into socket outlets
- Polarized The plug cannot be inserted upside down, reversing the live and neutral
The BS1363 plug has other salient features such as a long earth pin which ensures that appliances are earthed during plug insertion, before the two power pins make contact.
Plugs normally have grips at the edges to facilitate easier removal.
The flex exits from the bottom of the plug to discourage removal by pulling on the plug.
Doubly Insulated or Plastic Cased Appliances
Some appliances either have plastic, non conductive casings or are doubly insulated. A double insulated appliance has a casing which although it may still be metal, is sufficiently separated and insulated from internal live parts that there is no danger of it becoming live. These appliances are not earthed and only have a brown and blue core in their flex. i.e. no earth.
Double insulated appliances are either marked "double insulated" or more usually the symbol below is printed on the info label.
Cores or Conductors in a PVC Insulated Flex
Inside a Plug
Screw terminals are provided inside a plug for connection of the wires of a power cord, also known as a flex. A plug has 3 pins, live, neutral and earth as shown below. The terminals are clearly marked with the letters "L", "N" and "E".
Live and Neutral These 2 pins carry power to the appliance
Earth Under normal conditions, no current flows through this pin. However in the event of a fault in an appliance causing the metal casing to become live, this pin acts as a "bypass", shunting current away from the user. This trips the RCD and/or MCB at the electrical panel, shutting off power. The fuse in the plug may also blow (although the RCD may trip before this occurs). The earth pin also pushes open the safety shutters covering the live and neutral entry holes in a socket outlet when the plug is inserted.
When wiring a plug, it is essential to tighten the screws firmly down onto the bared wires of each conductor. This prevents arcing, overheating and potential fire.
Fuse A BS1363 plug is also fitted as standard with a ceramic, high rupturing capacity fuse. This protects the power cord and also the connected appliance from overload due to a fault. Plugs are usually supplied as standard with a 13A fuse. This is the maximum current that the plug can supply, and if an appliance tries to draw in excess of this current, the fuse will eventually blow. Fuses don't instantly blow once their current rating is exceeded. Instead they have a characteristic such that large overloads (e.g. due to a short circuit) will cause the fuse to blow in fractions of a second, whereas small over currents could take minutes to blow the fuse.
13A is equivalent to a load of almost 3kW at 230 volts, 50 Hertz (Hz), the EU standardised voltage and frequency.
Fuses should be replaced by BS1362 standard ceramic types. These fuses have a ceramic body which can withstand the likely high current (potentially > 1000A, depending on how far away you are from the supply transformer in the street) and energy dissipated as heat during a fault. Fuses shouldn't be replaced by types with glass bodies which can rupture.
If a lower powered appliance is connected to a plug, the fuse should be replaced by a lower rating fuse to suit the cord and appliance. 3A and 5A fuses are widely available corresponding to about 700W and 1150 watt respectively.
Strain Relief A strain relief clamp or cable grip is also provided, this must be screwed down onto the outer sheath or insulation of a cable, not the inner cores. Strain relief prevents tension on the cord during normal use from pulling wires out of the screw terminals.
Terminals in a Plug are Marked L, N and E
You will need:
- A flat bladed screwdriver. A phase tester is ideal and is a useful tool to have in your home toolbox. It has an internal neon bulb which can be used for detecting the presence of high voltage at socket or lighting outlets
- A wire snips (side cutters). You could also probably use a scissors
- A sharp knife
These tools should form part of your home tool kit. For more ideas on selecting tools for basic home maintenance or DIY, see this article: Selecting tools for DIY
Remove the Outer Sheath of the Power Cord
About 5cm or 2 inches of the sheath or outer insulation of the power cord must be removed. It is very important not to damage the insulation of the inner cores. You can snip down along the sheath if you have a snipe nose snips, alternatively score the sheath with the knife. Again you must be careful not to cut right through.
Scoring the Outer Sheath
Bend the Flex
Remove the sheath
Shorten the Live (Brown) Wire
Remove the Insulation from the Inner Cores
Remove the insulation from each conductor or core of the flex, about 10mm or just less than half an inch should be fine. You can either do this with a knife or use the snips. A snips is perfectly good as a wire stripper. With a bit of practice, all you need to do is grip the conductor, while cutting slightly through the insulation, and pull. Try this on some scrap flex first. Whichever way you bare the insulation, it's important to avoid breaking any strands of the copper conductor.
Strip the Insulation
Twist the Strands and Double Them Over
Twist the strands of each core of the flex and double them over. This keeps them together and stops them spreading out when the terminal screws are tightened. Doubling over the ends also ensures the screw has more wire to tighten down on. This is particularly important if the flex is light gage, in which case the screw may push the conductor out of the away as it is tightened, and only catch the edge of it.
Twist the Strands
Double Over the Ends
Loosen the Screws on the Strain Relief (Cable Grip)
When you feed the bared wires into the screw terminals, make sure they go all the way in and are caught properly by the screws. Screws should then be well tightened.
Feed the Brown Wire into the L (Live) Terminal
Connect the Green/Yellow Earth Wire into the E (Earth) terminal
Make Sure the Wires Are Caught by the Screw
Finally Connect the Blue Wire to the N (Neutral) Terminal
Tighten the Strain Relief and Replace the Cover
Checking the Fuse in a Plug
You can check whether the fuse in a plug is ok using a multimeter. In fact it's a good idea to have one of these in your home toolkit if you do any basic DIY. The DMM below is manufactured by Fluke, a reputable American manufacturer of electronic test equipment.
Checkout my guide to using a multimeter here:
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