Enclosed bus duct,abbreviated as bus duct,is a bus system composed of metal plates(steel or aluminum plates)as the protective shell,conductive bars,insulation materials,and related accessories.The enclosed busbar duct can be made into a plug-in type enclosed busbar with plug-in junction boxes at regular intervals,or a feeding type enclosed busbar without a junction box in the middle.Enclosed busbars can be divided into dense insulated busbars and air insulated busbars,suitable for three-phase four wire or three-phase five wire power supply and distribution lines with a rated working voltage of 660V,a rated working current of 250-2500A,and a frequency of 50Hz.Enclosed busbars have a series of characteristics such as compact structure,high insulation strength,large transmission current,good interchangeability,stable electrical performance,easy installation and maintenance,and long service life.Closed mother troughs are widely used in power supply and distribution systems in industrial and mining enterprises,high-rise buildings,and public facilities.

　　Enclosed bus ducts(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;Divided by purpose 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;According to the structure,it is divided into starting busbar duct,straight through busbar duct(with and without sockets),L-shaped vertical(horizontal)bent busbar,Z-shaped vertical(horizontal)offset busbar,T-shaped vertical(horizontal)three-way busbar,X-shaped vertical(horizontal)four-way busbar,variable capacity busbar duct,expansion busbar duct,terminal head,terminal junction box,plug-in box,busbar duct related accessories and fastening devices,etc.

　　The installation site for enclosed busbars should not exceed an altitude of 2000m;The ambient air temperature shall not be higher than+40℃and not lower than-5℃;Within 24 hours,its average temperature does not exceed+35℃;The relative humidity of the air should not exceed 50%at 40℃and 90%at 20℃;The surrounding air is clean and free of corrosive and insulating gases from Egypt.There are not only differences in concept and scope of use between enclosed busbars and enclosed bus ducts,but also other differences.The difference between enclosed busbars and enclosed bus ducts is quite significant,and the scope of bus ducts is obviously much larger than that of busbars.The bus duct system is a complete three-phase three wire,three-phase four wire,or three-phase five wire feeding and distribution system composed of more than ten types of bus duct unit structures,plug-in boxes,and other supporting components.And enclosed busbar only refers to the busbar units in the busbar trunking system.