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IV

The frequency of the alternating current in most parts of
Europe is 50 cycles. In North America it’s 60 cycles. Very high
frequencies are used in radio communication, sometimes several
million cycles.
Electricity can be very dangerous if it is carelessly used. A
faulty installation or a defective piece of equipment can cause a
serious fire and there is also the danger of an electric shock, with
possibly fatal consequences. Many precautions are taken and
safety devices are used to minimize these dangers. Insulation,
earthing, fuses and automatic cutouts are among the most
common safety devices.
Insulating is the converting of a conductor with a non-
conducting material to prevent it from touching another conductor.
The material used vary according to the nature of the conductor
and the condition in which it is used. It may have to withstand
extremes of temperature and resist corrosion. The insulation of
power leads to portable appliances must be flexible and also very
strong.
Any piece of electrical apparatus which has a metal body or
frame, especially portable appliances such as electric irons, kettles
and power tools, must be earthed as a safety measure. Farthing is
brought about by connecting the metal body or frame directly to
earth with thick conductor brings about earthing. In a three-pin
power plug the thickest pin is always the earth connection.
If a fault should develop inside the apparatus or if the
insulation on a flexible lead should break down, any possibility of
a person getting an electric shock by touching the apparatus will be
avoided because the current will take the easier path back to earth.
As an additional precaution the handles of all such
appliances are made of an insulating material such as rubber or
moulded plastics.
The most common safety device and one that is used in every
household installation is the ordinary fuse. This is simply a piece
of wire that is connected in series in the circuit. It is of such a
resistance that it will melt and therefore break the circuit if the

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