An Introduction To Electrical
Electricity is accepted as a normal part of everyday life and every year we put more and more appliances to use in our homes, some of them simple, like the kitchen toaster and some complex, such as a TV or a computer. Being a cheap source of energy, the demand for electricity has more than tripled over the past three decades. South Africa has one of the most sophisticated energy transmission systems in the world. Various types of processes may take place to provide us with this energy. The more obvious method is by burning material such as coal in a furnace, heating up water in a boiler into super heated steam, forcing the blades of a turbine into rotation and coupling this mechanically to a generator providing electricity. We see coal fired power stations all around the country with their tall cooling towers pouring out steam. Other methods include hydro-electric schemes which make use of gravity to force water through turbines. Solar and wind power, as well as nuclear power stations, all strive to provide one thing – electricity. Very often the electrical distribution in a home is neglected and left up to the electrician to decide where a light fitting should be placed or a plug point be positioned. Although his advice is invaluable and his knowledge of the regulations surrounding such installations necessary, input from the owner is very important.
Good planning and forethought on the number and nature of appliances to be used in the home becomes important information to the electrician when he sits down to design an efficient layout of the various circuits that will conduct electricity to appliances. The electrician on the other hand should not neglect the fact that the needs of the user should be taken into account wherever possible. A good working relationship with the owner is vital in order to minimise assumptions which always lead to disappointments later. All electrical appliances convert electrical energy into useful work. Proper distribution planning will ensure that every appliance is placed and operated correctly in the home.
Unit used as the measure of electrical pressure Symbol - V Analogous to Kpa pressure in water pipe. In South Africa the single phase voltage available for domestic use is 220 Volts (Between neutral and a phase). Normally appliances sold on the market are manufactured to operate at this voltage. Sometimes appliances have settings for various different voltage operations for use in other parts of the world – make sure that the setting is suitably adjusted for this country.
Unit used as the measure of electrical rate of flow. Symbol – A. Analogous to litres per minute in a water system.Each and every appliance connected to an electricity supply system will draw a certain amount of current in Amps when in operation. A toaster makes use of this current flow through a filament to generate heat in order to brown the toast. The light bulb is similar except that the heat generated is so high that light energy is given off.
Unit which shows the current drain of consumption of an appliance connected to a circuit. Symbol – W. Most appliances are rated in Watts. It is a very useful unit to determine the size and rating of a conductor for a particular appliance. A variation of the Watt is the Watt-hour and this unit shows the electrical consumption over a fixed period, in this case 1 hour. The electrical supply utility (In South Africa, Escom) makes use of this unit to charge for the use of electrical energy
A circuit may be described as a conductor (Copper wire) connected in such a way that electrical energy is allowed to flow through it. In household wiring there are normally two conductors that make up a circuit,one will be the live conductor and the other the neutral. Very often they will be colour coded to make identification of the type of circuit and conductor easy. A third conductor (normally a non insulated copper wire) is provided for an earth return, this is a safety feature should the insulation or proper connection of live conductors fail.
A Safety device which breaks the flow of electricity whenever a circuit is overloaded. Modern installations do not use fuses as safety devices any more, although in older installations they may still be seen. Each circuit will have a current rating. Should that current rating be exceeded, it becomes dangerous and may cause a fire, injury or even death. To prevent this, a fuse is placed in line with this circuit, always on the source side, and breaks the flow of electricity by overheating and melting. A fuse is chosen with a rating always slightly less than the maximum current rating of a circuit. Fuse wire is still readily available and is rated in Amps. More commonly, fuses will be found in some electrical and many electronic appliances to protect them from possible internal faults that may occur and cause large current flows that result in serious damage.
This is a device for breaking the flow of current. Switches come in various shapes and sizes but all operate on the same principle.An important factor when choosing a switch is its rating. A reputable manufacturer will always indicate the operating voltage and current rating. For instance, a light switch must not be used as a stove isolation switch, simply because the rating of the light switch will be too low for the stove current drain, causing it to overheat and fail.
Performs the same function as a fuse, but needs only to be reset, not replaced. These have now replaced the traditional fuses, and are chosen and connected into a circuit in exactly the same way. They are also known as contact breakers or trip switches.When the current flow in a circuit exceeds the rating of the breaker it will simply trip, cutting off the electricity supply to that circuit, protecting it from damage. Once the fault has been cleared, the circuit breaker is reset, thus restoring the supply. They are located in the distribution box of the house and also in the utility supply meter box. Every breaker should be clearly marked in order for faulty circuits to be easily identified and isolated.
Earth leakage unit
This device is able to detect small imbalances between the earth conductors and the supply, indicating leakage of electricity down to earth. A small test button is provided and should be used to test the unit periodically. It is a vital safety feature for any installation and should be installed.
Where the electrical supply is distributed from within the building. It usually houses all the contact breakers, earth leakage unit and may house items such as a door bell transformer and timers. Various sizes of distribution boxes are found, the main distribution box being in the house, and smaller boxes, together with contact breakers and possibly earth leakage units, at other points, such as swimming pool pumps, motors of gates and outbuildings.
A device may be used to switch the electrical supply on and off at predetermined times over a 24 hour period. The better known timer is the pool pump timer set at certain intervals to switch the pump on and off, filtering the water at regular intervals. This useful service alleviates the task of doing it manually and keeps it consistent.
If a voltage other than the mains voltage (220 Volts) is needed to supply electricity to an appliance, a transformer is necessary to step this voltage up or down. Low voltage lighting, as its name suggests, needs 12 Volts in order to operate safely and correctly; a transformer may be used to step the mains down to this level. A door bell transformer works on exactly the same principle. On the other hand, industry sometimes needs higher voltages than can be supplied by the Utility and uses transformers to step up to the required level.
AC, is the abbreviation for alternating current and DC for direct current. AC is the type of electricity supplied by the electricity supply utility to our industry and homes. DC is the type of electricity that would be supplied by a battery or an appliance such as a car battery charger where the voltage and current are constant. All the appliances found in our homes that operate on the mains supply are designed to work with AC. Some appliances however need batteries, such as portable radios: these work on DC.
Single phase denotes an electrical system or apparatus that has or uses only one alternating voltage. A polyphase system has more than one alternating voltage and three phase is a common system seen in larger domestic and industrial installations. Three phase being three alternating voltages displaced in phases relative to one another. If it is known that large loads are going to be required from an electrical source, for example a large house may need three 250 litre geysers apart from all the other appliances, a three phase installation will allow the various circuits to be shared between the phase, making it more efficient. For the average size dwelling however,a single phase installation is usually more than adequate.Your electrician will be able to advise you on the correct system for your needs. Bear in mind that there is a limit to the amount of current that is supplied to each user, this varies from area to area and the electrical supply utility or your electrician will be able to advise you.
The electricity meter is a very sensitive device that measures consumption in units of 1000 watts per hour and is expressed in kilowatt-hours. In modern installations,it will be located in a weather-proof housing just outside the yard and will more than likely have a peep hole so that the meter reader can take readings without having to open it. Older installations have been mounted on the same board that houses the contact breakers and/or fuses inside the building. This device makes it possible for the electricity supply utility to charge for the amount of electricity used over a period of time. The more electricity used, the more units indicated by the meter. The rate per unit will be multiplied by the total number of units for the period measured,giving a total value for the amount consumed.
In an effort to save energy, it has become common practice for many municipal supply utilities to install in residences a relay unit that is remotely controlled to switch off the geyser during a period when there is little or no demand. This has little effect on the individual household since the off time is relatively short but cumulatively, a sizable saving is achieved. The location requirements for these units does vary from area to area and where required must be installed.