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In electric power, a bushing is a hollow electrical insulator that allows an electrical conductor to pass safely through a conducting barrier such as the case of a transformer or circuit breaker without making electrical contact with it. Bushings are typically made from porcelain, though other insulating materials are also used.
The enclosure may also include fuses, isolating switches, load-break bushings, and other accessories as described in technical standards. Pad-mounted transformers for distribution systems typically range from around 100 to 2000 kVA, although some larger units are also used.
A padmount or pad-mounted transformer is a ground-mounted electric power distribution transformer in a locked steel cabinet mounted on a concrete pad. Since all energized connection points are securely enclosed in a grounded metal housing, a padmount transformer can be installed in places that do not have room for a fenced enclosure.
A grounding electrode conductor (GEC) is used to connect the system grounded ("neutral") conductor, or the equipment to a grounding electrode, or a point on the grounding electrode system. This is called "system grounding" and most electrical systems are required to be grounded.
Insulating supports are required at the points where they are supported by utility poles or transmission towers. Insulators are also required where wire enters buildings or electrical devices, such as transformers or circuit breakers, for insulation from the case. Often these are bushings, which are hollow insulators with the conductor inside them.
Sometimes the fittings are considered sufficiently conductive to bond (electrically unite) the metal conduit to a metal junction box (thus sharing the box's ground connection); other times, grounding bushings are used which have bonding jumpers from the bushing to a grounding screw on the box.
Arcing horns protecting bushings on a distribution transformer. Arcing horns form a spark gap across the insulator with a lower breakdown voltage than the air path along the insulator surface, so an overvoltage will cause the air to break down and the arc to form between the arcing horns, diverting it away from the surface of the insulator. [3]
Bushing (bearing), a type of plain bearing; Bushing (electrical), an insulated device that allows a conductor to pass through a grounded conducting barrier; Bushing (isolator), a mechanical device used to reduce vibrational energy transfer between two parts; Drill bushing, a tool used to guide the placement of a hole when drilling in a workpiece