Two types of wiring are used in the domestic electrical circuits. Fixed cables are normally concealed, and carry electrical current to switches, ceiling lights, and socket outlets. Flexible cords (flexes) connect portable appliances and light fittings to the fixed wiring.
This consists mostly of PVC-sheathed cable containing three copper conductors (cores). The core insulated in red PVC is the ‘live’ and the one in black the ‘neutral’ though in lighting circuits in the cable to the switch both the black and red are live. (The black core is required to have a piece of red sleeving on it to indicate this, although this is often omitted by incompetent electricians. Cables having two red conductors are made for contract work, but rarely stocked and sold retail). The third core is the earth and this is uninsulated, but when exposed after the sheathing is removed ready for wiring up it must be sleeved in green/yellow striped PVC before being connected to the earth terminal. In some wiring circuits PVC-sheathed cables having one core only are used, for example, where a live core is looped out of a switch or a neutral core is looped out of a light, to supply an additional light or lights. Three-core and earth cable is used for two-way switching. The conductors are insulated in red, blue and yellow; the colour coding is for purposes of identification only.
Flexible cords are made in various sizes and current ratings and the types you’ll most often come across are: and Each conductor is made up of a number of strands of copper and it is this which gives the cord its flexibility.
The insulation used round the conductors now conforms to an international colour coding standard.
– brown denotes the live wire, blue the neutral, and green/yellow the earth, when it is part of the flex.
Transparent or white insulation is used for a flex that carries a low current and where it doesn’t matter which wire is connected to the live and neutral terminals of an // appliance. It is used mainly for table lamps that need no earth. ‘blows’ and cuts off the current flow.
The earth conductor links socket outlets and appliances (via their plugs) and is connected to a main earthing terminal at the house fuse box or consumer unit. This is usually connected to the outer metal sheath of the underground supply cable.
All metal pipework in the house is also earthed by being connected to the earth terminal – this is called ‘cross bonding’.
Wire. These insulating materials deteriorate with age (about 25-30 years) so the wiring can become dangerous. Therefore it really does need to be replaced with modern PVC-sheathed and insulated cable
Cables for fixed wiring
Most domestic wiring is now supplied in metric sizes which refer to the cross-sectional area of one of the conductors, whether it is composed of one or several strands of wire. Most common sizes of cable are 1.0mm2 and 1.5mm2 used for lighting, and 2.5mm2 used for power circuits.
Cable with grey sheathing is intended to be concealed in walls or under floors; white sheathing is meant for surface mounting.
Safety with electricity.
– never work on a circuit with current on. Turn off at mains and isolate circuit by removing relevant fuse. Keep this with you until you restore supply.
– never touch plugs and sockets with wet hands
– remove plugs from socket when working on appliance
– always use the correct fuse wire when mending a fuse The importance of earthing
Earthing is an essential safety feature of all wiring systems. To complete a circuit, electricity either flows down the neutral conductor of the supply cable or it flows to earth. That is why you get a shock if you touch a live wire. The idea of earthing is to connect all metal fittings and appliances in the house with a good conductor – the ‘earth wire’ in cables and flexes. If a fault occurs that makes this metal live, the presence of the earth wire prevents the voltage from rising much above earth voltage. At the same time, the fault greatly increases the current being drawn to the metal via the supply conductor, and this current surge is detected by the circuit fuse, which
Some old installations may still be using lead-sheathed or tough rubber-sheathed (TRS) wiring, with the conducting wires insulated in vulcanized rubber, or vulcanized rubber insulated, taped and braided
The right connection
The plug is the vital link between any electrical appliance and the mains and must be connected up correctly if it is to do its job properly. With flex in the new colour codes, connect the Brown core to the Bottom Right terminal, the Blue core to the Bottom Left one and the green-and-yellow core (if present) to the top terminal. With cores in old colour codes, Red goes to the bottom Right terminal, Black to Bottom Left and green to top.
Old colour codes
Before the introduction of new international colour codes, flex used red insulation to denote the live conductor, black for the neutral and green for the earth.
Warning: Electricity is dangerous
In some countries, including Australia, West Germany and the USA, regulations stipulate that all home electrical work must be carried out by a qualified electrician.