Electricians in London

Electricians in London

Lighting

How much light do you need?

The various activities carried out in the average home require not only different types of lighting, but also different amounts of light. In technical terms the requirements are expressed in lumens per square metre. (To convert them to lumens per square foot, divide by 10.) For general use a living room should have a light intensity of 100 lumens per square metre (10 per square foot). Light reading requires 200, prolonged reading (or studying) 400. Sewing or close work calls for 600 lumens per square metre.

You could achieve this necessary versatility by having a ceiling light fitting which provides sufficient light for general purposes, supplemented by spots or table lamps. Additional light will be needed near or above chairs or work surfaces. The average requirements for other rooms are kitchens-200 lumens per square metre (particularly over work surfaces); bedrooms about 50 lumens per square metre with provision for a 200 lumens headboard light for the late night reader.

Most other rooms including landings and halls need about 100 lumens. Stairs, at their treads, ought to have 50-100 lumens to be absolutely sale with control switches at both the top and bottom of the staircase. It is simple to calculate the wattage required to provide these standards of lighting as long as you know the efficiency with which the lamp converts electrical energy into light-in other words, the number of lumens per watt. A fluorescent tube provides about 50 lumens per watt. So, for example, if the light intensity needed in a kitchen is 20 lumens per square foot the wattage required using a fluorescent tube will be 20 + 50 =0.4 watts per square foot. Thus, one 40 watt fluorescent lamp will provide the equivalent of 20 lumens per square foot over an area of 100 square feet (0.4 x 100). Metallic filament bulbs are far less efficient than fluorescent lamps, producing approximately 12 lumens per watt. Daylight has hundreds of lumens per square foot but it is generally easy on the eye because it is so evenly distributed.

Ceiling lights

Fittings that are mounted on the surface of the ceiling, or even recessed into it are a comparatively modern development. They can be spotlights, or more conventional fittings with diffusing glass or louvres which are excellent for general lighting. Spots are ideal for reading because they provide beamed, concentrated light; the light shines directly onto the book and the reader is not sitting in his own shadow. These lights can be grouped to provide high light intensity where it is needed, giving reflected light throughout the rest of the room. Not many people will want to start cutting holes in their ceilings to accommodate recessed light fittings.

A less messy and inconvenient alternative would be the installation of a false ceiling beneath the existing one. This may be worth considering if your present ceiling is either badly cracked or very high (more than 2.5m). Tackling a whole ceiling can be an ambitious project, but you may be able to fit a false ceiling across part of a room. This is particularly easy in a house that has a reinforcing beam in some of its ground floor ceilings, supporting a bay or ground floor extension. This would enable you to fit a false ceiling to the depth of the beam. With two or three concealed lights built into your new ceiling, there would be no ugly cables showing and there would be the effect of softly diffused light. Try to forget about the traditional habit of placing a light in the centre of the ceiling. Several lights dotted all over the room are more interesting than a single fitting, although an off centre ceiling light can only be really efficient if other lights are available to illuminate the rest of the room. Greater flexibility can also be achieved with ceiling lights if they are fitted with a dimmer switch. These simply replace your present switch and enable you to raise or lower the level of lighting by simply turning a dial. In this way, you can, for example, tone down powerful reading lights for relaxing.

New ideas

Even in the more conventional lighting fields such as ceiling mounted or suspended fittings, there is a wide range of choice and something to suit every taste. The bayonet-type fitting, remains the most popular. Designs are available to suit the mood of every room and they have the advantage of being extremely diverse.

Rise and fall units ceiling suspended lights which are height adjustable-are also useful and versatile. When used in the ‘up’ position they provide general lighting. In the ‘down’ position they throw a pool of light into a limited area, creating an intimate atmosphere. They are most commonly used for dining table fittings and are particularly suitable for this, although they could also be used over a desk top or sewing machine, for example. Many people choose a standard lamp for a reading light or to cut down glare when watching television. These will be more efficient if fitted with a large shade, which gives a wide pool of light. Small shades also tend to make bulbs overheat, thus shortening their lives, because they prevent the free circulation of air around the bulb.

Flourescent lights

Fluorescent tubes are often considered boring, dazzling and useful only for garages. This need not necessarily be the case. They can have many effective and efficient uses in the home and are always worth considering because of their cheapness to run. The slightly chilling effect they sometimes have can be eliminated by using one of the warmer shades such as ‘De luxe warm white’. ‘Warm white’ provides a high light output (measured in lumens per 305mm and is very efficient in large kitchens. It is ‘sharp’ enough for work surfaces where efficiency is important, and yet warm enough to be comfortable to work in. ‘Natural’ is closest to day-light but is probably the least acceptable for domestic use since it gives a cool, blue-white appearance. Daylight itself reflects ‘true’ colours because it contains all the colours in the spectrum: red, orange, yellow, green, blue, indigo and violet. Artificial light, in general, contains a much narrower range of colour, which is why fabric shades, for example, look so different under department store lights. Artificial light gives either a cold or a warm effect and you must know what is best for your needs. Candlelight or firelight contains more natural red/orange and gives people a healthy, flattering glow. Fluorescent blues tend to have bluey tones which give a colder effect. This is why they are often recommended for use in purely service rooms where you need a good light rather than an intimate atmosphere. Despite its occasional chilliness, fluorescent light has much to recommend it. Because the length of tube eliminates light shadows, a 40 watt tube gives approximately the same amount of light as a 150 watt metallic filament bulb and spreads the light over a wider area. And with an estimated life of 7,500 hours, a tube lasts at least seven times longer than a bulb.

Another advantage is that the tube never gets overheated; you can even fix one behind a pelmet with no danger of your curtains catching fire. Fluorescent tubes are available in a range of lengths from 30cm to 244cm and your choice of length depends on the output needed. For example, a 15 watt l5in. tube would be ideal for lighting a bathroom mirror, and a 40 watt, 1.2m tube would be fine for a small kitchen. The installation of fluorescent fittings presents no particular difficulties. The body of the unit is screwed to the wall or ceiling through distance pieces, designed to provide a space of about 6mm between the back of the unit and the surface to which it is fitted.

This is to allow some circulation of air round the tube. The wiring is equally straightforward, being clearly marked on the terminal block fitted inside the unit. Some fittings have push-button switches so that they need not have a switched electrical supply and these are particularly useful for fitting over a bedhead. While unshielded tubes are ugly, they have a stark, utilitarian air, and you may prefer to use them only in less sophisticated areas, such as a workshop or kitchen. The tubes can be made more attractive, however, by fitting them with diffusers, although some output efficiency may be lost as a result. There is a wide range to choose from: extruded reeded plastic, natural raffia, and various fabric finished diffusers. They are designed to give a soft upward light, with a stronger downward light to illuminate areas of special interest. Diffusers usually clip to the tube itself, or to the fitting, and are easily removed for cleaning.

Spotlights

Although a new lighting scheme has ultimately to be planned for the whole house, it can be tackled gradually. One of the easiest, cheapest and most effective experiments you can try is to purchase and place a spotlight. Theatrical designers and shop window dressers have realized-and exploited- the dramatic potential of spots for many years. A figure on the stage, or a garment in a shop window, can be made arresting and dominating by the simple expedient of focusing spotlight on to it. Spotlights are now supplied specifically for the home and, used with a little imagination, they can do much to enliven a room. Because they are fully adjustable, both vertically and horizontally, even one lamp, carefully placed, can be used to illuminate a favourite painting, for example, and then turned to throw intense local light on a work surface such as a desk.

Apart from wall fittings, they can be placed on the floor as elegant uplighters, flitted to standing frames or ceiling tracks, or clamped to a bedside fitment for a reading lamp. Domestic spotlights are mostly small, neat and unobtrusive. The light and not the lamp catches the eye or should if it is properly placed. As well as ensuring that they do not give a blinding light, spots must also be positioned away from fabrics or any inflammable materials as they produce a considerable heat.

Normally, spotlights are fitted with special, internally silvered reflector lamps, but you can also buy general service lamps adapted with clip-on auxiliary reflectors. Versatility is the great merit of spotlights. Installation is simple: they screw into place, and are wired like any other wall or pendant light. Some have push button switches, so they can be wired into an unswitched circuit, without the need to run new cables back into the switch for other lights in the room. If you want to flt them to the ceiling, spotlights should be sited one to two feet from the wall. Placing them depends on what you want to illuminate. Spotlights should ‘spot’ something-be planned to pick out one area or object. Installed at random, much of their effect is lost.

Lighting design

Lighting can be fun, formal, and flattering. Experimenting with it is fun, too, but the secret often lies in simplicity. A single spotlight focused on a favourite picture is a simple idea, but can be more effective than a dozen badly placed standard lamps. Planning lighting carefully can give your home a new dimension. Because of the technicalities involved, many people tend to fight shy of making drastic changes to the lighting in their homes, preferring to leave it to the experts.

But traditional lighting in the home is usually conservative, and often inadequate. By exploiting the potential of the many different fitments that are readily available, you will be able to achieve both effect and efficiency in your lighting system-and without completely rewiring your home. Unless you are lucky enough to be in on the planning stage of building a new house, you will probably find that your home has been wired unimaginatively. Builders tend to be conventional and provide only the standard lighting points in the traditional positions-a centre ceiling light, two wall plugs per room, and perhaps a couple of wall light outlets on either side of a fireplace or in an alcove. It is all too easy to allow your choice of lighting to be moulded by what is there-and obvious rather than plan out exactly what each individual room needs.

After all, planning takes time and energy. But if you can find enough of these to bother, the rewards will be considerable. When choosing your lighting fitments, try to decide what you want before you go shopping. Department stores tend to be discouraging to new ideas. Their lighting departments are usually a blaze of fittings, all switched on at once, with tittle attempt to demonstrate individual effects. It is hard to visualize what a specific fitment will look like away from all the others in the shop and hanging in your home. Confused and unsure, one can so often end up with buying the same style fitment or lights as before, with the feeling that it is better to be sale than sorry.

Home wiring circuits

The various circuits in a dwelling are detailed below.

Lighting circuits
A lighting circuit is wired in either 1.0mm2 or 1.5mm2 cable using either of two methods. One is the loop-in system where the cable from the 5A fuse runs to each ceiling rose or other lighting fitting and terminates at the last on the circuit. From each light a cable is run to its switch which if a 2-way switch, a 3-core and earth cable is run from this switch to the second 2-way switch. The other method is the joint-box system where each light and its switch requires a separate 4-terminal joint-box. The cable from the 5A fuse runs to each joint-box in turn and terminates at the last joint-box in the circuit. From each joint-box a cable is run to the light and another cable to the switch. A lighting circuit may supply up to a maximum of 10 lighting points which is the equivalent of about 1200 watts.

Ring circuits
A ring circuit is wired in 2.5mm2 cable. The cable starts from the terminals of a 30A fuse, runs to each socket outlet it is to supply and returns to the consumer unit where it is connected to the same terminals as the first end of the cable. Cables termed spurs may branch off the ring cable at socket outlets or joint-boxes to supply remotely positioned outlets. A ring circuit may supply an area of up to 100 square meters or 7200 watts maximum load.

Socket outlet circuit
The maximum load for this type of wiring is 3000 watts.

Spur on a ring circuit
This type of wiring is effectively a branching off a ring circuit and the maximum load is the again 7200 watts.

Single appliance circuit
This type of wiring is necessary for power hungry appliances, for example electrical showers, cookers, electrical heaters.

House and flats wiring cables

The fixed wiring in a house or flat supplying the various circuits is usually flat, twin-core and earth PVC sheathed with some sections of a lighting circuit such as 2-way switching being wired in flat 3-core and earth PVC sheathed cable. The sheath is either grey or white. Within the sheath of twin-core and earth cable are two PVC insulated, current-carrying, copper conductors: one red, one black and an uninsulated copper conductor positioned between them.

The red conductor is normally used as the live and the black as the neutral, but the return wire from a switch to the light of a lighting circuit although live when the switch is’ON’is a black wire which needs a red sleeve slipped over each end. The uninsulated wire is the earth conductor and its bare end within a switch or any other accessory must be enclosed in a green yellow PVC sleeve, so that it does not make contact with a current carrying terminal. Core colours of a 3-core and earth cable are red, yellow and blue, and when used in a switch circuit the,ends of the blue and yellow conductors must be enclosed in red sleeving. Sizes of cables used in home wiring are 1.0mm2, 1.5mm2, 2.5mm2, 4mm2, 6mm2 and 10mm2.

Mending fuses in a fuse box

Always have a card of fuse-wire available, these cover the most popular current ratings: 5, 15 and 30 amps. Make sure you rewire a fuse with the correct size fuse wire using the colour code as a guide to the size required. For cartridge fuses, always have at least two spares of each current rating in the consumer unit. Locate the ‘blown’ fuse and remove the fuse holder. Take out the bits of old fuse wire or the old cartridge and insert the new one, taking care not to stretch the fuse wire on tightening the terminal screw, as this would decrease the current rating, lead to heating of the wire and premature failure. Before replacing the fuse holder in the consumer unit try and find out why the fuse ‘blew’. If the new fuse blows immediately there is a fault in the circuit which requires attention.

Miniature circuit breakers

(MCBs) An MCB is simply a single pole switch which automatically trips (switches-off) when there is a fault in the circuit or serious overloading. To restore the current you simply switch on the MCB but if there is a fault in the circuit it is impossible to close the circuit breaker until the fault is rectified. MCBs can also be used to switch off individual circuits when required, or leave a circuit supplying a freezer or refrigerator switched on when leaving the house for an extended period.

Home wiring

In older electrical installation, the wiring is divided into a number of circuits each having a specific current rating. The current ratings are determined by the current ratings of the circuit fuses or MCBs in the consumer unit and protecting the circuits. There are five old standard ratings: 5, 15,20,30 and 45 amps but rarely does a consumer unit include all five ratings. Some homes only have 5A circuits, for lighting only, but most have 5A. and 30A fuses: the 30A being for ring circuits supplying 13A socket outlets, and a separate 30A fuse for the cooker and another 30A fuse for the instantaneous shower unit. Immersion heaters are usually supplied from either a 15A or 20A fuseway and night storage heaters from 20A fuse usually from a separate consumer unit under times witch control set for the overnight cheap rate. Where the cooker is of extra large size it is supplied from a 45A fuse.

Circuit fuses
Circuit fuses are in two types: rewirable, using fuse wires, and cartridge type where the fusing element is enclosed in a cartridge similar to but physically larger than the fuse in a 13A plug. The cartridges are of different dimensions according to their current rating. This, unlike a rewirable fuse makes it impossible to uprate a fuse by inserting one of higher rating which could lead to overloading the circuit wiring, which in turn could result in a fire. The fuse units of both types are colour coded according to their current rating. The old colours are: white (5A); blue (15A); yellow (20A); red (30A);and green (45A).

Electrical terms

Although there are numerous terms used in electrical engineering those which really concern the householder are volts, amps and watts. A volt is the unit of electrical pressure which as already explained is standard at 240Y in the UK from the mains supply.
Apart from being lethal this comparatively high voltage makes it essential that all ‘flexible cords, cables, switches, socket outlets and other accessories used in home installations are of the correct type designed for 24OV , working without any likelihood of leakage of dangerous currents which would result in fire and shock. In addition it is imperative that electrical work is done properly and is correctly maintained by qualified electricians to prevent leakage of dangerous currents,

The amp is the unit of current, and this determines the sizes of flexible cords and cables and the current capacity of electrical wiring accessories, that is, switches and socket outlets. The watt is the unit of power and represents the electrical loading of a lamp or appliance and therefore the current consumption. The watt is the product of the voltage and current; multiply the volts by the current and the result is the wattage. 1000 watts equal 1 kilowatt. A 1KW appliance switched on for one hour consumes 1KWH (1 unit) of electricity. Electrical appliances are usually rated in watts (or KWs). To calculate the current in amps when the wattage is known, so that the correct size of flexible cord or cable is chosen, divide the watts by the voltage. For example, a 2-bar electrical fire having a loading of 2000 watts consumes 2000W / 240Y =8.4 A.