Insulators are materials which prevent the flow of heat (thermal insulators) or electric charge (electrical insulators). The opposite of electrical insulators are conductors and semiconductors, which permit the flow of charge (Note: a semiconductor is strictly speaking also an insulator, since it prevents the flow of electric charge at low temperatures, unless it is doped with atoms that release extra charges to carry the current). An electrical insulator may sometimes be known as a dielectric.
A perfect insulator is impossible to achieve due to the second law of thermodynamics. However, some materials (such as silicon dioxide) are very nearly perfect electrical insulators, which allows flash memory technology. A much larger class of materials, e.g. rubber and many plastics, are "good enough" insulators to be used for home and office wiring (into the hundreds of volts) without noticeable loss of safety or efficiency.
High voltage insulators used for high voltage power transmission are either porcelain insulators or composite insulators. Porcelain insulators are made from clay, quartz or alumina and feldspar. Alumina insulators are used where high mechanical strength is a criterion. In recent times there is a shift towards composite insulators which have a central rod made of fibre reinforced plastic and outer weathersheds made of silicone rubber or EPDM. Composite insulators are less costly, light weight and have excellent hydrophobic capability and hence can be used in polluted areas.
Collectible insulators
Glass insulators were, and in some places are still used to mount electricalpower and signalling lines used for telephone, telegraph, fire, and other electrical applications. Colors and design details varied widely because many of the insulators were made by small, local manufacturers. Clear and blue-green insulators are the most common.
Collecting insulators became a widespread hobby starting in the late 1960s. Since then, many people have joined the hobby, and there are many places to ask questions, trade or just talk to collectors. Collectors classify insulators according to CD numbers (Consolidated design number system develpoed by N.R. Woodward) with the shape, size, wire groove location and inner skirt all taken into account.
Electricalinsulation is the absence of electrical conduction.
Electricalpower cables may be insulated with polyethylene, PVC, rubber (natural or synthetic), impregnated paper, teflon, or even compressed inorganic powder, depending on the application and voltage class.
Flexible insulating materials such as PVC (polyvinyl chloride) or neoprene are used to insulate the circuit and prevent human contact with a 'live' wire.
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