In electrical power distribution, a bus bar is a strip or bar of copper, brass or aluminum that conducts electricity within a switchboard, distribution board, substation, battery bank or other electrical apparatus. Its main purpose is to conduct electricity. The cross-sectional size of the bus-bar determines the maximum amount of current that can be safely carried. A bus duct is metal bar that supports and contains a group of electrical bus bars. The duct comes in standard 10 foot lengths. The greatest advantages of the bus ducts is that they are capable of adding or removing a branch circuit without removing voltage from the whole duct.