These operate at elv (extra low voltages) between 3 and 12 V. The single bell, buzzer and many models of chimes are powered by dry batteries but the more powerful chimes and intricate bell systems have to operate from mains transformers. Usually a transformer is preferable for any bell or chimes. Where an illuminated bell push is used a mains transformer is essential as the lamp of the push would exhaust a battery in a day or so. 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 »
Some fluorescent fittings have no starter switch(s) for the tubes. Instead there is S transformer to provide the prewarming and the tube itself has a metal stripe running throughout its length from one lamp cap to the other. The lamp caps are earthed at the lampholders.
This assists in the starting of the electron flow and, as there is no starter to operate, the lamp strikes without the characteristic delay of the switch-start type.
A fluorescent tube has an expected life of 5000 to 7000 light hours or up to seven times that of an electric light bulb. 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 »
Formerly imperial ratings were used for fuses and circuit breakers, but the international Renard ratings have now been added and will supersede them.
Fuse manufacturers are still using the imperial sizes while circuit breaker manufacturers have mostly changed to the new ratings. An equivalence chart is shown above.
The miniature circuit breaker (MCB) is now widely used and overcomes all the problems associated with ordinary fuses. It is a small, sophisticated unit affording a much higher level of protection than an ordinary fuse. It is tamper-proof and the unit involved is easily identified when one has tripped (the switch moves to the ‘off’ position). Most importantly, MCBs cannot be reset if the fault still exists; this eliminates the foolish and highly dangerous practice of putting in the wrong fuse wire or cartridge just to get things ‘conveniently’ working again for the time being. Read the rest of this entry »
A basic understanding of electricity is essential, even for those who do not intend to carry out any repairs or servicing of appliances. Ignorance is no protection against your own or someone else’s errors and oversights, whether with repairs, servicing or installation.
Power is supplied to an electricity substation at a very high voltage — 400,000 volts — in three-phase form. There it is converted, via a transformer, to 230 volt single-phase for distribution to our homes. In normal circumstances, current flows from the live supply of the substation’s transformer, through the electrical appliances used in the house and back via the neutral conductor (cable) to the substation transformer’s neutral pole (a closed loop). Read the rest of this entry »
The earth path of an appliance can be checked easily using a simple test meter. Remember, path of low resistance is required from all items within a appliance that are linked into the earth path via the yellow and green cable.
The earth path of an appliance from its exposed metal parts to the earth pin of the plug should be a maximum of 1 ohm (BS3456).
Checking the earth path of a socket requires an earth loop test meter which needs to be operated correctly. This is an expensive item and, moreover, problems may be encountered with distribution boards fitted with an RCD. It is, therefore, advisable to have these tests done by a qualified electrical contractor. Read the rest of this entry »
Problems with electrical appliances may not always result from a failure of the equipment itself. They can be caused by the failure of electrical supply to the appliance via the socket. A three-pin socket must have a live supply, a neutral return and a sound earth path. When a plug from an appliance is inserted, firm contact must be made at all three points. If the live or neutral pins of the plug or connection point within the socket fail to make adequate contact or are free to move, localized heating will occur within the socket. Typical signs of this problem are listed below.
There are various reasons for such problems. They may be caused by one or a combination of any of those listed here. Read the rest of this entry »
When an appliance is in use small sparks are generated at mechanical contacts, such as those found in switches and the junction between motor brushes and commutator. This results in the emission of spurious radio waves that can be heard as crackles on radio or television receivers or that are passed down the mains circuit to audio equipment. The suppressor is designed to eliminate the formation and transmission of these spurious radio waves. They are also known as mains filters. Read the rest of this entry »
