Different types of cameras use different methods to focus their lenses, but with the common aim of providing the photographer with a sharp image on the film.
Focusing is either done by guessing or actually measuring the camera-to subject distance using a rangefinder. The lens is then set manually to the correct distance, or in some cameras the range finder is coupled to the focusing mechanism. In other focusing systems the image is seen through a ground-glass screen and the lens moved until the image is sharp. Read the rest of this entry »
A wall light is fixed by its baseplate either to a box sunk into the wall or it is fixed direct to the wall. The box, termed ‘BESA’ box, is a termination box to contain the ends of the circuit wires from which the sheath is removed, and a flex connector which joints the wires to the flex of the fitting.
Only wall lights having a baseplate with 50 mm (2 in) fixing centres to match the lugs in the box can be mounted on this circular box. Most wall lights have other types of baseplate of which there are many shapes and sizes. Read the rest of this entry »
There are two principal methods of wiring a lighting circuit, the loop-in system and the joint box system. In practice a circuit is often a mixture of both methods, the principal sections being loop-in with some lighting points being wired in conjunction with joint boxes to save cable and to facilitate the wiring. For both methods twin-core and earth PVC sheathed cable is used.
In the loop-in system, ceiling roses combine the functions of ceiling rose and joint box as the circuit wires are jointed at the ceiling rose terminals. The flexible cord of the pendant is connected to the rose terminals. Read the rest of this entry »
Socket-outlets situated off the main route of the cable do not have to be connected to the actual ring cable. Instead they are usually supplied from spur cables branching off the ring. These spurs are wired in the same size cable as that used for the ring.
Fixed appliances which may be connected to a ring circuit include skirting heaters, wall heaters, small water heaters and any non-portable electrical appliances having individual loadings of not more than 3000 W(13 A approx.). Read the rest of this entry »
A radial power circuit is the name given to a circuit supplying a number of 13 A socket-outlets and fixed appliances using one cable which is not wired in the form of a ring but terminates at the last outlet.
The permitted number of socket-outlets (and fixed appliances) depends on the current rating of the circuit which can be either 20 A, wired in 2.5 mm2 cable, or 30 A wired in 4 mm2 cable. The number of socket-outlets and fixed appliances which can be served by a 20 A radial circuit depends also on the location of the circuit and whether the outlets are confined to one room. Read the rest of this entry »
Of the two principal types of cooker control unit, the type incorporating a kettle socket-outlet is the more popular. Since, however, it is important that the kettle is not used on the cooker hob where its flex would trail over a switched-on boiling plate it is better to have the unit without a socket where it has to be fixed immediately above the cooker. Read the rest of this entry »
Electric heating of water can be carried out in a variety of ways. These include small capacity heaters fitted above the sink, instantaneous sink heaters or immersion heaters in the hot water tank.
Small storage water heaters fitted over the sink or washbasin having capacities of up to about 3 gallons and electrical loadings of 1 to 3 kW are usually supplied from the ring circuit by means of a spur. Except in a bathroom, the outlet can be a fused plug and switched socket-outlet, preferably with neon indicator. Read the rest of this entry »
Joint boxes are usually circular and for part of the circuit wiring. They are fix permanently to the house structure are used principally in lighting circuits. Join boxes are available in 4- 5- and 6-terminal versions.
A 3-terminal joint box of 30 A current rating is used for ring circuits to connect spur cables to the ring cable, as shown the illustration. Read the rest of this entry »
Take particular care in the bathroom where special regulations apply.
Do not install a socket-outlet in the bathroom other than an approved shaver supply unit for a mains voltage shaver.
Do not make provision for using a mains voltage portable appliance. For example do not run a portable electric heater from a socket-outlet situated outside the bathroom i.e. on the landing or in an adjacent bedroom. If the tank cupboard opens into the bathroom and the tank has an immersion heater do not supply it from a socket-outlet (not a good method in any case) which could be used for plugging in a portable appliance. Read the rest of this entry »
Many household appliances have some means of governing the temperature at which they operate. Examples include the regulation of high temperature ovens and heaters by switching elements on or off and, at the other end of the scale, the control of low temperatures in refrigerators and freezers by turning the compressor motor on or off.
A thermostat is an automatic device for regulating temperature. They range in type from the simple single action switch, which turns off or on at one pre-set temperature, to the fully adjustable type, which can be adjusted within a given range. Read the rest of this entry »
