A closed busbar duct is a busbar system composed of metal plates(steel plates or aluminum plates)as protective shells,conductive bars,insulation materials,and related accessories.It can be made into a plug-in enclosed busbar with plug-in junction boxes at regular intervals,or a feeding enclosed busbar without a junction box in the middle.In the power supply system of high-rise buildings,power and lighting lines are often set separately,and enclosed bus ducts are installed vertically along the wall in the electrical shaft as the main power supply line.

　　Bus ducts are generally composed of starting bus ducts,straight through bus ducts(with and without sockets),L-shaped vertical(horizontal)bent busbars,Z-shaped vertical(horizontal)offset busbars,T-shaped vertical(horizontal)three-way busbars,X-shaped vertical(horizontal)four-way busbars,variable capacity bus ducts,expansion bus ducts,terminal heads,terminal junction boxes,plug-in boxes,related accessories and fastening devices of bus ducts according to their purposes.Bus ducts can be divided into three types according to insulation methods:air type plug-in bus ducts,dense insulation plug-in bus ducts,and high-strength plug-in bus ducts.According to its structure and purpose,it can be divided into dense insulation,air insulation,air additional insulation,fire-resistant,resin insulation,and sliding contact busbar trunking;According to its shell material,it is divided into steel shell,aluminum alloy shell,and steel aluminum mixed shell bus duct.

　　Air type plug-in bus ducts are rarely used in the south due to the use of copper sheet soft connections between the joints of the busbars.In humid weather in the south,oxidation is prone to occur between the joints,resulting in poor contact between the joints and the busbars,making the contacts prone to heating.And the volume between the joints is too large,the horizontal bus segment size is inconsistent,and the appearance is not aesthetically pleasing.Dense insulation plug-in bus duct(CMC).Its moisture-proof and heat dissipation effects are poor.In terms of moisture prevention,the busbar is prone to moisture and water leakage during construction,causing a decrease in insulation resistance between phases.The heat dissipation of the busbar mainly relies on the shell.Due to the compact arrangement and installation between wires,the heat dissipation of L2 and L3 phases is slow,resulting in a high temperature rise in the busbar duct.The dense insulation plug-in bus duct is limited by the shell plate and can only produce horizontal sections no larger than 3m.Due to the small air gap between the busbars,a strong electric force is generated when the busbars pass through high currents,causing the magnetic oscillation frequency to form a superimposed state and resulting in excessive noise.

　　High strength enclosed bus duct(CFW).Its manufacturing process is not limited by sheet metal,and the shell is made in the form of tile grooves,which increases the mechanical strength of the busbar.The horizontal section of the busbar can be produced up to 13m long.Due to the shell being made in the form of a tile groove,the position of the groove intentionally separates and fixes the busbars,with a spacing of 18mm between the busbars.The ventilation between the lines is good,which significantly improves the moisture-proof and heat dissipation functions of the busbar trough,making it more suitable for the southern climate;Due to the gap between the wires,the temperature rise of the wires decreases,which increases the overload capacity and reduces magnetic oscillation noise.But the stray current and inductance generated by it are much larger than those of dense bus ducts,so when comparing with the same specifications,its conductive busbar cross-section must be larger than that of dense insulated plug-in bus ducts.Plug in busbar trunking belongs to the trunk system,which has the advantages of small volume,compact structure,reliable operation,high transmission current,easy tapping and feeding,convenient maintenance,low energy consumption,and good dynamic and thermal stability.It is widely used in high-rise buildings.