The first thing to learn about electricity in the home is how it works and what it does. Having grasped the basic principles, most of the work you may want to tackle will be that much easier to understand and carry out correctly.
Find out where electricity comes from and where it goes and know the various types of cable and flex and what they are used for.
Check your own consumption so you can work out where savings can’be made. Save time and money by being able to diagnose the fault, whether you repair it yourself or call in the expert. And check on the major danger area of the home — the bathroom.
Basics of electricity
Electricity is the source of energy for heating, lighting and powering many appliances in your home. In knowing all about it, you can tackle all sorts of repairing and fitting jobs safely.
Rather like the water supply, electricity comes into most homes from some unknown outside source: but how does it arrive and what is it? Pushing down a switch gives immediate light and power to drive fans, cleaners and kitchen equipment; it also provides gradually increasing heat in kettles, cookers. Fires, immersion heaters and central heating. But beyond this point electricity is to most people a mystery, and to many something to be feared. Some people even think that electricity leaks out of every power socket without a plug in it, or lamp-holder that does not have a bulb in it. An understanding of the simple principles of how electricity works can help to remove the fear.
Although it may help you to understand electricity by comparing it with the water supply, it is important to remember that this is only an analogy; the electricity supply is in some ways similar to the water supply, but it is quite wrong to suppose it will continue to behave like water in every respect. Electricity will only flow in a conductor; you can compare this to water flowing in a pipe. But while water will keep flowing out of a broken pipe, electricity will not continue flowing out of a broken wire unless there is some other conductor — a screwdriver, a hacksaw blade, some other metal or wet material — to conduct it away. The reason is that electricity does not really ‘flow’, it is much more like the hydraulic fluid that operates the brakes of a car or the big jacks used in constructional engineering.
Hydraulic fluid transmits pressure along a pipe from one place to another and if the pipe is cracked, or there is not enough fluid, the system will not work. In the same way, electricity supplied to the home at a certain ‘pressure’ is used to do the work of driving motors, or making heat and light.
The earth will conduct electricity very easily. The human body will not conduct it so easily, but easily enough. If you touch the bare end of a ‘live’ wire, or the contacts in a lamp-holder when the switch is on, the electricity will be conducted through your body to the earth. If you are lucky, the electricity will make your arm muscles jerk away as soon as you touch the wire, and you will only suffer an electric ‘shock’. If you are unlucky, the electricity will make your finger muscles clamp onto the wire so that you cannot let go. You may die by electrocution or at the least be badly burned and anyone who tries to help you by touching you will suffer the same. In this situation the helper must switch off the electricity or, failing this, try sharply jerking the afflicted person away with a rope, tea towel or scarf, or anything non-conducting (that is, not metal or a wet material) like a broom.
DC or AC
Electricity can be supplied in two ways in domestic circumstances: as direct current (DC) or as alternating current (AC). All batteries — the lead battery of a car, the ‘dry cell’ of an electric torch or transistor radio, or the rechargeable battery of certain pieces of portable electronic equipment — supply DC. So do many private domestic generators, such as used to be installed in houses and farms far away from public supplies. The national electricity grid now provides AC supply to all but the most remote areas of Great Britain. Light bulbs and simple heaters will work equally well on DC or AC supply, but most modern electrical equipment is made to operate on AC only, and needs special modification for DC supply.
This term denotes the pressure exerted by the electricity supply. So a torch battery, at 1.5 volts, will give you no more than a tiny tingle if you put your wet tongue across the contacts; but don’t try the same thing with your home supply at 240 volts!
It is easy to understand how the electricity from a DC source such as a battery can be imagined as exerting this pressure; but what about AC? In an AC supply the ‘direction of flow’ of electricity changes backwards and forwards, usually 50 times every second. The ‘mains supply’ enters your home as two wires: a ‘live’ wire (L) at a pressure of 240 volts, and a ‘neutral’ wire (N), which is connected to the earth. The live wire is coloured red and the neutral wire black.
The ‘earth’ wire
Why, then, is there a separate earth wire inside the home? The reason is that the neutral wire is only conducting to earth while everything is working properly. If a live wire works loose, or its insulation is worn away, it may touch the outside casing of an appliance; this is why any metal part of an appliance that can be touched, switch plates, lamp-holders etc. should be independently connected directly to earth by means of the earth wire.
Current and resistance
To understand a little more about electric current. You have to go back to comparing it with water flowing in a pipe. Suppose there is a pump A, which drives water through the pipe B. The
system will only work if there is a complete circuit back to A. The pump A can be thought of as the electricity source, and it will only drive the turbine D if the tap C is open. So C is equivalent to a switch in an electrical circuit, and D is any appliance put into the circuit.
The flow of the water round the pipe circuit is like the ‘flow’ of electricity in an electrical circuit. As more water per second flows through D, so it will do more work. In the same way, the greater the quantity of electricity flowing each second in the circuit, the more work it will do. The quantity of electricity per second, called current, is expressed in amperes (or amps for short). But here, once again. You must remember that electricity is not really like water. For instance, if you consider the statement ‘more water is flowing per second’, you think of it as flowing faster; but electricity always ‘flows’ at the same speed, and it is the amount of work it is capable of doing that changes. Imagine instead that the water is always flowing at the same pressure and the same speed, but being pumped through pipes of bigger bore.
You can also see that if the pipes were made narrower, it would become more and more difficult to get the water to flow, until eventually the pipe was so narrow that the pressure would not be sufficient to drive the water through. At all. The narrow bore of the pipe is therefore exerting resistance. In the same way, part of an electrical circuit can be a resistance. In passing this resistance, the electricity does work. The work may consist of driving a motor or be in the form of heat or light. If there is no resistance to the electric current, electricity will flow through the circuit in such quantity that it is as if a pipe has burst: it can (almost literally) ‘drain’ the supply. This is why fuses are put into every part of the home electricity supply. If there is a ‘short circuit’, the large current flowing through the thin wire of the fuse heats it up and causes it to melt — breaking the circuit and stopping the flow.
Volts, amperes, ohms and watts
Resistance is measured in ohms. The relationship between volts, amperes and ohms is very easily expressed: volts = amperes x ohms.
As the domestic AC supply is at about 240 volts, and the safety limit for ordinary appliances is set at 13amps, you can calculate that the minimum resistance a circuit can offer is about 18 ohms.
The work that the electricity does is measured in watts. If you look at the manufacturer’s plate on any electric appliance you will see that it is rated at so many volts (220-240 volts, AC 50 cycles) and so many watts. The relationship between watts, volts and amperes is: volts x amperes = watts. The pressure of the electricity supply — its voltage — does not normally change. The working appliance consumes electricity at a fixed rate. If the domestic supply is at 240 volts, and the appliance is rated at 960 watts, it will be consuming current at the rate of 4amps, which is within safe limits. If the total ‘load’ of appliances on any one domestic circuit adds up to more than 7200 watts, the current will exceed 30amps and the consumer unit fuse may ‘blow’.
One thousand watts equal one kilowatt (kW) and electricity consumed over a period of one hour is called a kilowatt-hour (kWh), or one ‘unit’ of electricity. Electrical consumption is measured and charged for on this basis.