A busbar is a strip or bar of copper, brass, or aluminium that conducts electricity within a switchboard, distribution board, substation, battery bank, or other electrical apparatus in power distribution. Its primary function is to conduct electricity, not to serve as a structural member. The maximum amount of current that can be safely casted is determined by the cross-sectional size of the busbar. Busbar can have a cross-sectional area as small as 10 mm2, but electrical substations may use metal tubes with a diameter of 50 mm or greater as busbar. Large busbar will be used in an aluminium smelter to carry tens of thousands of amperes to the electrochemical cells that produce aluminium from molten salts.