bus bar

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1500 ampere busbars within a power distribution rack for a large building

In electrical power distribution, a busbar is a thick strip of copper or aluminium that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus.

The size of the busbar is important in determining the maximum amount of current that can be safely carried. Busbars can have a cross-sectional area of as little as 10 mm² but electrical substations may use metal tubes of 50 mm in diameter (1,963 mm²) or more as busbars.

Design and placement

Busbars are typically either flat strips or hollow tubes as these shapes allow heat to dissipate more efficiently due to their high surface area to cross-sectional area ratio. The skin effect makes 50–60 Hz AC busbars more than about 8 mm (1/3 in) thick inefficient, so hollow or flat shapes are prevalent in higher current applications. A hollow section has higher stiffness than a solid rod of equivalent current-carrying capacity, which allows a greater span between busbar supports in outdoor switchyards.

A busbar may either be supported on insulators, or else insulation may completely surround it. Busbars are protected from accidental contact either by a metal enclosure or by elevation out of normal reach. Neutral busbars may also be insulated. Earth busbars are typically bolted directly onto any metal chassis of their enclosure. Busbars may be enclosed in a metal housing, in the form of bus duct or busway, segregated-phase bus, or isolated-phase bus.

Busbars may be connected to each other and to electrical apparatus by bolted or clamp connections. Often joints between high-current bus sections have matching surfaces that are silver-plated to reduce the contact resistance. At extra-high voltages (more than 300 kV) in outdoor buses, corona around the connections becomes a source of radio-frequency interference and power loss, so connection fittings designed for these voltages are used.

Gallery

Bus duct penetration, awaiting firestop.

Electrical conduit and bus duct in a building at Texaco Nanticoke refinery in Nanticoke, Ontario, 1980s.

Bus duct section subsequently used in fire test of a firestop system, achieving a 2 hour fire-resistance rating.

See also

• Electrical bus

References

• Walter A. Elmore. Protective Relaying Theory and Applications. Marcel Dekker Inc.. ISBN 0-8247-9152-5. 

External links

Wikimedia Commons has media related to: Bus Duct

• Paschal, John (2000-10-01). "Ensuring a Good Bus Duct Installation". Electrical Construction & Maintenance. http://ecmweb.com/mag/electric_ensuring_good_bus/. Retrieved 2009-04-06.