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 »
Don’ts
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 »
All the mains appliances featured here have some kind of mains cable. Problems with the electronic cables of portable appliances are quite common, especially those that are moved around constantly while in use, such as vacuum cleaners and hedge cutters.
The problems can range from a simple break in one or more of the conductors, which would render the appliance open circuit, to the breakdown of the cable’s insulating properties caused by damage, fatigue or neglect, leading to the risk of electric shock or fire. Electronic cables and extension leads must be checked regularly and thoroughly.
There are several different types of flexible electronic cable in two-core and three-core configurations on the appliances shown here. It is important to remember that two-core electronic cable is used only on double insulated appliances; three-core electronic cable is used on all items requiring an earth connection. Read the rest of this entry »
The term ‘harness‘ is used for all of the wires that connect the various components within an appliance. In large appliances they are usually bound or fastened ‘together in bunches to keep the wiring neat and safely anchored. Smaller appliances, however, may sacrifice neatness for safety and route the wiring to avoid contact with heat or sharp edges. The correct positioning of wiring also contributes to the double insulation of an appliance, so no alterations whatsoever should be made to the routing or position of the wiring in double insulated appliances.
When you first take a look at it, the harness may seem like a jumble of wires thrown together, but if you take the time to inspect it, you will find that each wire is colour-coded or numbered either on the wire itself or on the connector at each end. This allows the engineer to follow the wire through the appliance easily. With a little practice, any wiring or coding can be easily followed. 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 »
A huge variety of household appliances contain heating elements. The two basic types are the exposed single-wire element, most often used in hairdryers, fan heaters and toasters, and the metal-sheathed element used in ovens, grills, iron sole plates and immersion heaters.
This type of element is simply an exposed length of conductor which heats up when a current is passed along it due to the resistance properties of wire. As it is an exposed conductor, it must be housed and supported in a way that avoids accidental contact which could cause electric shock or burns. It must also be housed in a way that allows the heat generated to dissipate and do the job intended. For instance, a toaster needs a large aperture in which to place the bread so that it rests near the exposed element for it to function correctly. Read the rest of this entry »
Capacitors used for motor starting may have metal or plastic outer casings with an insulated top with two terminals. Internally the two terminals are connected to two sheets of metal foil with an insulator between. This package of large surface area is rolled into a cylinder which fits into the shell of the capacitor. As the voltage supplied to one terminal is alternating (at 50 times per second), so does the polarity of its connected foil. An opposite movement of electrons is induced in the other foil, even though they are insulated electrically. This causes a delay in the electrical path, and this, in the case of an asynchronous induction motor, gives the outof-phase feed to the start winding. Read the rest of this entry »