Insulator
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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). The term electrical insulator has the same meaning as the term dielectric, but the two terms are used in different contexts.
A perfect thermal 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, for example, 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.
Among naturally-occurring substances, mica and asbestos have performed well as both thermal and electrical insulators, until the advent of better synthetic (man-made or man-modified) products.
See also: insulation
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High voltage insulators
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 electrical power 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. Green or aqua insulators are the most common due to the iron content of the sand used in making glass, but the most popular colors among collectors come in various shades of purple and amber. Insulators made of clear glass typically indicate a more recent manufacturing date. Most insulator manufacturers stopped making glass insulators in the late 1960's, switching to ceramic materials. Collectors classify insulators according to CD numbers (Consolidated design number system developed by N.R. Woodward) with the shape, size, wire groove location and inner skirt all taken into account.
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. The National Insulator Association is a non-profit educational and scientific organization, created to encourage insulator collecting and to protect the interests of its members and collectors. It has established standards and ethics by which its members may fairly deal with each other.
See also
External links
- http://www.myinsulators.com/downtownseattle/ — one person's obsession with telephone pole insulators
- Transcontinental Telegraph Insulators, 1867 (http://CPRR.org/Museum/Ephemera/Brooks_Insulator.html)
- www.insulators.com
- www.insulatorscanada.comda:Isolator
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