Busbar

In electric power distribution, a busbar (also spelled bus bar, or sometimes as buss bar or bussbar, with the term bus being a contraction of the Latin , "for all", or buss being short for buttress) is a metallic strip or bar (typically copper, brass or aluminium) that conducts electricity within a switchboard, distribution board, substation, battery bank, or other electrical apparatus. Busbars are used to carry substantial electric currents over relatively short distances; their greater surface area (compared to a wire of the same weight) reduces losses due to corona discharge. Busbars are not normally structural members.

The material composition and cross-sectional size of the busbar determine the maximum amount of current that can be safely carried. Busbars can have a cross-sectional area of as little as 10 square millimetres (0.016 sq in), but electrical substations may use metal tubes 50 millimetres (2.0 in) in diameter (20 square millimetres (0.031 sq in)) or more as busbars. An aluminium smelter will have very large busbars used to carry tens of thousands of amperes to the electrochemical cells that produce aluminium from molten salts.

Busbars are produced in a variety of shapes such as flat strips, solid bars and rods, solid or hollow tubes, and braided wire. Some of 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 millimetres (0.31 in) thickness inefficient, so hollow or flat shapes are prevalent in higher current applications. A hollow section also has higher stiffness than a solid rod of equivalent current-carrying capacity, which allows a greater span between busbar supports in outdoor electrical switchyards.

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