Introduction: How to Wire / Terminate a UK 13A 3 Pin Plug
Here is my very first Instructable. Being an electrician and having bought an import item with a foreign plug on it, I thought I would make this Instructable to set out the Do's and Dont's for terminating cables into a 13A 3 pin plug.
It's a sad fact that a lot of people simply don't know where to start in tackling this task. I myself used to do this when I was a child, using a butter knife as a screwdriver and my teeth as wire strippers but I now use propriety tools that make the job a lot easier.
To complete this task with the upmost ease, four tools are needed;-
A small to medium (around 6-8mm across) flat blade screwdriver.
A terminal screwdriver (around 3-5mm across).
All these tools come in many forms and shapes. If you're going to be doing this task a lot then I recommend buying quality tools. CK, Knippex, Facom and Bahco are all great names and quality you can trust but come with a price to match. If you are only going to do this now and then, cheap basic tools will be fine.
Step 1: Inspect Item to Be Terminated.
Give the power cord a quick once over to check for damage. There is no point putting a new plug on a power cord that is damaged.
The item I have is brand new and free from any damage. The next step is to remove the old plug. The plug I have is a moulded case Chinese 3 pin plug, so my only option is simply to cut it off with my wire cutters. I am making sure to cut the cable as close to the plug as possible as to keep the power cord as long as possible. The cable is the same from appliance to plug so you can cut where ever you like but obviously, the closer to the appliance you cut the cable the shorter the cable will be.
Step 2: Strip Back the Outer Sheath / Insulation
The next step is to remove the outer sheath that surrounds the inner insulated wires. About 50mm should be removed. An easy way to know how much should be removed is to hold it up to the back of the new plug that the power cord is going to be terminated into. The amount removed should be the same as the length of the back of the plug.
The removal of the outer sheath can be done in many ways. Luckily for me I can simply use my automatic wire strippers but another way to do it is to gently score around the circumference of the cable with a stanley knife about 50mm from the end (taking extra care not to cut through the insulation of the inner wires), then bend the wire until it separates from its self, then slide off the sheath that is to be removed.
Step 3: Dismantle the New Plug
Next is to dismantle the new plug that the power cord is going to be terminated into. As I do a lot of PAT testing I happen to have a lot of brand new ones lying around but you can purchase them at lots of places including Wilkinsons for around £1-£2. Or you can take a plug off an old appliance that you no longer use, providing it is not a moulded case plug.
One matter of great importance is to make sure it is fitted with a correctly rated fuse. Not having the correct fuse could lead to the appliance being damaged by excessive current. The way to decide what fuse to be fitted is fairly simple. Firstly check the power consumption of the appliance in Watts, then divide that value by the supply voltage. The appliance I have has a maximum power consumption of 600W and the supply voltage in the UK is 230v. I simply divide 600 by 230 which is a rough answer of 2.61. Therefore a 3A fuse is required for this plug. Always use a fuse that is as close to but over the rating in Amperes of the appliance. Using a fuse that is less then the rating will just blow as a soon as it is powered up.
The three main fuses used in the UK are 3A(red), 5A(black) and 13A(brown) although fuses of many different ratings can be found.
All British Standard 13A plugs that are not moulded have three screws on the pin side. A large centre screw and two smaller screws underneath. The large centre screw is the case release screw and the two smaller screws are the cord grip screws. Loosen the centre screw using the larger screwdriver until the plug separates in to two halves. Then loosen the the two lower screws just enough to allow enough room for the power cord to be able to slide in. Try not to over loosen the lower screws too much as to separate them from the cord grip as this is not necessary and leads to more effort having to be put in to reassemble the plug.
Step 4: Identify the Cores, Cut to Length and Strip Back Insulation
The next step is a very crucial one. This is where most people get it wrong and can often lead to dangerous terminations of power cords.
In the UK and harmonised throughout the EU, core colours are brown for the live, blue for the neutral and green and yellow for the earth. These three coloured wires are found in CAT I appliances, only brown and and blue are found in CAT II appliances. CAT II appliances are 'double insulated' throughout the appliance which means an earth wire is not needed. CAT II appliances are signified by the 'square inside a square' symbol.
A lot of people assume that all three wires should be the same length inside a plug. This is a common error and can lead to dangerous terminations, trapped wires and excess wire outside of the plug.
Firstly, lay the power cord over the plug to get an idea of the amount of cable to be cut off. An old school way of remembering which colour goes where is bRown right, bLue left and earth in the middle.
Then form the wires to where they shall rest inside the plug making sure to leave enough to reach right through to the other side of the screw terminal. Notice how the brown wire is a lot shorter then the other two. This is important and is actually a safety feature. Should the cable receive a sharp enough tug as to pull the cable out of the plug, the brown wire will be pulled out first as it is the shortest and removed any danger of electric shock. If it was the other way round, the live would still be connected and a loose neutral would be sticking out causing a very dangerous situation.
Then strip off the insulation. Strip off an amount equal to the depth of the screw terminal. If the conductor size is small, 0.75mm or less, double the amount that is stripped and then double over the end of the copper to get a good, secure termination.
Twist the copper to form a tight thread and place in to the terminals and tighten the screws until the copper is secure.
Tighten the cord grip screw to secure the power cord in place and then replace the plug top and tighten the centre screw.
Sit back and admire your work.