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 type enclosed bus duct with plug-in junction boxes at regular intervals,or a feeding type enclosed bus duct without a junction box in the middle.In the power supply system of high-rise buildings,the power and lighting lines are often set separately,and the bus duct is installed vertically along the wall in the electrical shaft as the main power supply line.

　　The manufacturing process of high-strength enclosed busbar trunking is not limited by sheet metal,and the shell is made into a tile groove form,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.

　　The surface treatment of the conductive enclosed busbar shell is an important task,which includes processes such as acid washing,phosphating,drying,powder coating,and curing.The shell coated with polyester epoxy powder has strong surface adhesion and can maintain insulation for a long time.Conductive copper bars are composed of pure copper bars,and the surface of the conductive copper bar joints should be uniformly plated with tin or silver.The insulation material is composed of high-strength insulating plastic blocks made of polytetrafluoroethylene and polycarbonate.Fixed bolts,insulation sleeves,and cover plates.The installation site for enclosed busbars should not exceed an altitude of 2000m.The surrounding air temperature should not exceed+40℃or-5℃,and the average temperature within 24 hours should 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.

　　The enclosed bus duct adopts a non-magnetic material aluminum alloy shell with good conductivity as the protective ground wire,which is surrounded by the conductive busbar.Due to its proximity to the three-phase busbar as much as possible,it can achieve low reactance,and the distance between the protective ground wire and the three-phase busbar is equal,with the same reactance.In this way,whether it is a short-term or continuous relative ground short circuit fault,this grounding method is better than setting up a separate PE row.Therefore,the International Electrotechnical Commission has announced and advocated the use of enclosures as grounding conductors for electrical busbars(bus ducts).The traditional protective earth wire PE line is placed on one side of the bus duct.Due to electromagnetic induction,the fault current induced on the protective earth wire is 50%higher than calculated by actual measurement.At the same time,the distance between the three-phase conductive rows and the PE line is uneven,and the inductance is also uneven.When the line is long,the three phases are severely unbalanced under fault current.