Light, heat and power
Electricity is converted into light or heat by being directed along a wire too small for the flow of electrons. This gets hot and glows. The intensity of light or heat depends on the wire or element.
To provide power, an electric motor rotates. Motors are of two basic types-the brush motor and the induction motor. The brush motor is made up of two sets of electro-magnets, an outer set, called the stator or field coil, and the inner, which revolves, called the armature. The shaft which works the appliance is connected to the armature, and revolves when this spins.
Whenis switched on, the coils of the stator and those of the armature become poles-north and south. North poles attract south and a motion is set up. This type of motor can be used with either AC or DC current.
Induction motors work on AC, which automatically reverse flow many times a second, reversing the current flow when a north and south pole come together.
Electricity enters the home by means of a service cable terminating at a sealed company fuse box. This cable has three conductors-two plastic-sheathed ones-red for live and black for neutral-and a bare, or earth, wire. Electricity flows along the red wire and returns along the black. All fuses should be placed in the live side of a line or cable.
The electricity company’s fuse box contains a fuse of high amperage, 60 amps, and is designed to protect its supply cables and the local transformer from damage.
This box should never be tampered with. The electricity board alone must deal with faults at the company fuse box and back from it.
Some homes have an additional meter. This is coloured white and records the consumption of off-peak electricity, used with electrical storage heaters and immersion heaters.
The fuse box or consumer unit, fulfils two purposes. It is a safety as well as a control point for the household electricity. It enables the electricity, entirely or in part, to be shut down, and it provides master fuses.
The fuse is a vital part of the electrical system. It is usually housed in porcelain or bakelite ‘carriers’ on fuse boxes. It contains a piece of wire thinner than the rest of the circuit, which melts and breaks the circuit if the circuit becomes overloaded or a short circuit develops.
On modern fuse boxes there is usually one fuse for each circuit, rated in accordance with the load it has to carry.
Another type of unit is called a miniature circuit breaker. This does not carry fuses, but if a fault develops the unit shuts off and cannot be switched back on until the fault has been corrected. The domestic fuse box is connected to the company’s equipment by means of heavy-duty cable, called ‘tails’.
On fused plugs the fuse is in the form of a ceramic cartridge.
In early days of electricity fires were common, caused by overloaded wiring, because fuses were not generally used.
In older installations, the mains switch may be separate from the fuse box. If the switch is part of the fuse box, this points to the fact that m modern wiring is probably installed.
Supply needs to the home are generally grouped as follows:
• Upstairs lighting • Downstairs lighting (including porches)
• Upstairs power points
• Downstairs power points
• Cooker (where fitted)
• Garage and workshop
Sometimes upstairs and downstairs lighting are grouped on one circuit and the domestic power on another. With larger properties, it is usually desirable to use the separate circuits. Lighting circuits are rated at 5A. Many houses have more than one circuit, since the maximum current is 12kW at 240V.
Modern lighting is either of the junction box or loop-in variety. The junction box is used as a connector to feed various lights individually. The loop-in principle takes electricity from light to light in turn.
Older power circuits consisted of radial wiring, each fed back to the fuse box and individually fused, usually at 15A. Modern practice is to use a ring main.
As the name suggests, all the points are linked as one circuit or ring; this spreads the electrical load over the whole circuit. The rating is 30A and the maximum load for a ring is 7-2kW. Fuses may not blow, however, until twice this load has been attained.
Spur points, individually fused, can be taken from a ring circuit. These should not exceed 50 per cent of the total number of outlets. Fused, flat, three-pin plugs and matching sockets are used on ring circuits. These can, if chosen, be individually switched off, though this does not affect the circuit operation.
Many homes have too few power points and rely on a single centre light for each room. It is a good rule to have points distributed at intervals of about 1830mm; this reduces the amount of running flex when appliances are plugged in.
Rooms are better and more pleasingly lit by a variety of lights: wall lights, standard or table lamps and more than one ceiling light.
These can also be coupled with dimmer switches to control light intensity. This not only conserves the life of the lamp but cuts the electricity bill.
Electrical wiring falls into two categories – fixed and flexible. Fixed wiring consists of three conductors, two sheathed and coloured red (live) and black (neutral) with an unsheathed earth. Flexible wiring is brown (live), blue (neutral) and green and yellow (earth).
Modern cable is sheathed in PVC and has an indefinite life. In the course of any rewiring you may have to connect metric cable to existing imperial cable. This will set no problem, provided the slight difference in amperage rating is borne in mind and the new wiring is still within the current-carrying capacity of the circuit.
You will need a basic number of tools. These should include at least two sizes of screwdriver, both with insulated handles and one with a small blade and the other a larger blade, a small pair of pliers for nipping the wires of cables and a cable stripper.
A, for drilling into walls, a hammer and bolster for chasing out walls would also be useful.
10. November 2011 by admin
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