For safety reasons, all new electrical appliances purchased in the UK should have a plug fitted, however, if you have some older appliances a plug would not have been fitted at that time.
The flex that fits into and connects the plug electrically will usually have three insulated wires (conductors). Each has a different coloured insulator or plastic cover; Brown, Blue and Yellow and green. All three are further insulated by what is known as the sheath, which is the outer plastic cover.
Before we continue the process of fitting the flex to a plug, it is important to understand some basic requirements, or electrical rules regarding what these colours stand for.
The [brown] insulator is the ‘Live’ conductor.
The [blue] insulator is the ‘Neutral’ conductor.
The [yellow] and [green] insulator is the ‘Earth’ conductor.
Please note that in this article the wires covered in the brown, blue, and yellow and green plastic insulator will be referred to as ‘Conductors’.
Before new regulations were introduced in the 2004 the insulator colours were red for ‘Live’, black for ‘Neutral’ and green for ‘Earth’.
The casing of the plug is made of plastic, and has three protruding metal 'pins' two of which (Live and Neutral) should be partially insulated to reduce the risk of touching a 'live' circuit when inserting or removing the plug. These pins are what make the electrical connection when the plug is pushed into the wall socket. When the casing screw is removed and the cover of the plug removed, the tops of these pins can be seen. These are known as the terminals to which the flex conductors are attached. You will notice too a fuse (or the clips to accept a fuse) on the right hand side of the plug.
The terminals are made in two forms, either stud terminal which clamps down onto the conductor, or the post connectors which have a small hole to receive the conductor with a small screw at the top which secures the conductor in place.
It follows then that the three terminals of the plug are designed to receive the three conductors of the flex, and if you examine the plug closely it will be seen that each terminal is identified with the letter L, N and E, (Live, Neutral and Earth) on the plug. You will also see a symbol used for Earth. The ‘Earth’ is situated at the top, the ‘Live’ goes to the right and connected to the fuse clips, and the ‘Neutral’ is on the left (viewed inside with the cover of the plug removed with the Earth at the top).
At the point where the flex enters the plug there will be a cord grip which secures the flex so that if it is accidentally tugged it does not put strain on the conductors. The retention method on your plug will be one of the two types used, screw down retention bar as shown here (above left), or a plastic jaw (as shown in the bottom righthand image on the page).
After removing the cover from the plug, place the flex over it so that it extends beyond the earth terminal, and mark the sheathing at the entry point (beyond the cord grip). The sheathing will now need to be removed up to this point. To do this, bend and nick the sheathing with a utility knife without penetrating the individual insulated conductors beneath it where the tension of the bend will split and enlarge the nick. Repeat this process around the sheathing until the cut goes all around. Remove the sheathing to expose the three insulated conductors.
Because of the arranged position of the terminals, each conductor will need to be cut to different lengths so as to reach the corresponding terminal comfortably. To do this, reposition the flex over the plug so that the sheathing is just beyond the flex clamp and the coloured wires extend beyond the earth terminal. Position each conductor towards its corresponding terminal following the channels in the plug. The Brown conductor which goes to the right hand side that is connected to the fuse should be cut to a length that comfortably reaches the terminal without being taught. The Blue conductor should be to a length that it has a gentle bend as it enters into the terminal, and the earth conductor should be slightly longer than required. Don’t forget to allow for the portion of the conductor that enters into the terminal, or as in the case of the stud terminal, the amount of the conductor required to be hooked around the stud.
The image on the right shows the conductors fitted with the Earth slightly longer. The reason for this is that in the event that the flex receives a severe tug resulting in the live conductor being pulled out of its terminal, the longer Earth conductor is less likely to become detached because of having more slack, thereby maintaining an earth connection in the event of a short.
The insulation can now be removed from the end of each conductor, using wire-strippers or a sharp utility knife, and the amount removed depends on the type of terminal used. In the case of the pillar terminal about 10mm should be sufficient where as with stud terminal 12mm may be required. When the insulating material has been stripped back, twist the inner strands of copper conductor together.
Now the flex can be permanently fixed to the plug. First position the flex in the flex clamp so that the end of the sheathed section is within the clamp area, and screw down the crossbar onto it. In the case of the jaw system, simply push the sheathing between the jaws ensuring that there is a good portion of the sheathing available within the plug in both cases.
Connect each conductor to the correct terminal. With the pillar terminals, fold the exposed copper conductor in half so that it is a double thickness, loosen the screw and insert the conductor and tighten the screw to secure. In the case of the stud terminals, unscrew the nut and captive washer, bend the copper wire into a hook shape and wrap it around the stud in a clockwise direction and tighten.
Fit the correct rated fuse into the fuse clips, replace the plug cover and secure it in place with the screw provided with the plug.
Congratulations, your plug is now ready to use.