In this article I will explain the skeleton of how a home electrical installation works. The content of this article is very basic. It is not for technicians or engineers. It is for those people who have been using electricity all their lives without knowing at all how it works, how it causes fire or how it kills people.
The electrical current that goes into our homes come from the electricity supply company's distribution network, usually in the form of overhead cables running on concrete poles or using cables buried one meter below the ground. When the cables reach a residential house, they usually enter the house through the front entrance and connect to a meter panel. Together with the meter on the panel is also a cut-out fuse. The meter and the fuse usually belong to the supply company. From the meter panel the electrical cables go to the home distribution panel. On the panel are usually an isolation switch, a leakage protection circuit breaker and a few outgoing fuses or outgoing circuit breakers. From the outgoing fuses or circuit breakers the wiring cables run above the ceiling, inside or on the surface of the wall, or concealed inside the concrete floor to go the lamps, ceiling fans, socket outlets and other equipment like the toilet exhaust fans in our homes.
When a home user connects an electrical appliance to a socket outlet, the connection is usually made by the use of an electrical cord. One end of the cord has a plug unit (sometimes the plug unit contains a fuse) that is inserted to the power socket (i.e.wall plug). The other end will be plugged to another socket already built-in on the appliance. Now and then the location of the electrical appliance need to be quite a few meters away from the wall socket outlet. The electrical cord provided with the appliance is usually between one to one and a half meters long. In these cases home users usually purchase an extension cord to connect between the wall socket and the appliance's electrical cord.
From the viewpoint of the electrical current flow, the supply uses only two wires. That is why in some countries or regions we can see only two big wires coming down from the electric pole to a house. One of them is called the live wire, "hot" wire or phase wire. It is this wire that is "dangerous". The second wire is called the neutral wire or the "return" wire. The electric current flow into the house will come out again (i.e. return) in the same magnitude and goes back into the supply company's transformer or generator. This electrical path forms a complete "loop", like a circle. The continuous and circulating flow of this electrical current is what makes the filament inside the house incandescent lamp burns and produce light that brightens our house. This behaviour of the home electrical system brighten and enrich our lives. When used and handled properly, electricity is very useful and friendly. It is however very powerful and dangerous, and therefore must be treated with respect.
With the two wires described above, we can have electricity in our home that can keep our food fresh in the refrigerator and replace the candles to light up the house during the night. However with just these two wires, it is like driving an car at high speed without the brake. Driving the car without a brake is extremely dangerous even on an empty freeway that has no traffic light for hundreds of kilometers at three in the morning. As in driving, we need to step on the brake now and then to slow down, or during an emergency.
In a home electrical system, this braking is accomplished through a third wire, the earth wire. Many electrical terms are commonly used for this wire such as earthing wire, ground wire, chasis wire or protective wire. In a house, this earth wire is almost always colored green or green with yellow stripes. The wire connects the metal casing of the electrical appliance in our homes to the "earth body". (Really, it is actually connected to the huge mass of the earth.) When the "hot" or live wire somehow come into contact with the outer metal casing of your washing machine, for example, then the fuse at the distribution board will immediately blow, stopping the current flow to the metal casing of the washing machine so we do not get the shock, a fatal shock actually. Where the distribution board uses a circuit breaker instead , the circuit breaker immediately trips, cutting off the supply just like the fuse does.
If the green wire is broken, or it does not connect properly along its path to the earth body, then the electrical power has no brake. The person touching the washing machine's metal casing can get electrocuted.
So do treat the electrical wiring and electrical appliances in your home with respect. Safety comes first. In future articles I will explain more on the "earth wire" and I will also give more tips and techniques on how to make sure your home electrical installation is safe for you and your family.