IP Electricity and energy © Oxford University Press 2011 Electricity and energy

IP Electricity and energy © Oxford University Press 2011  When an electrical charge flows through a resistor, the resistor gets hot.  Energy has been transformed from electrical energy into heat energy.  This heating effect occurs in all types of resistance not just resistors. Therefore the cables themselves and all electrical devices generate heat depending on their resistance.

IP Electricity and energy © Oxford University Press 2011  Normally this heating effect is unwanted and causes devices to be less efficient.  Filament lamps transfer a much higher percentage of electrical energy to thermal energy than compact fluorescent lamps do.  When you are buying new devices you can check how much energy they waste by looking at the efficiency rating label on the packaging. A device which wastes less energy will have a higher rating. The most efficient devices are rated A++.

IP Electricity and energy © Oxford University Press 2011  The heating effect can have much more drastic consequences. A fuse is a safety device that melts and breaks the circuit if the current is too high in a circuit.  A fuse is simply a piece of wire in a cartridge. Think of what would happen if there were too much current going through the wires in the cables connecting devices or in the wires inside the devices themselves. These cables would melt or catch fire.  Using the correct size wire is important for the amount of current in each application and device.  Those with very low currents can be much smaller (like this cable of data communication wires) than ones with higher current (like the cables for a domestic electrical appliance cord). Mains cables into your house need to be much larger as they carry an even higher current.