Bus ducts are the main power lines,and any problems can have a significant impact.It involves issues such as energy loss,voltage drop affecting equipment,and potential safety hazards.So quality control of bus ducts is very important.The selection and application of bus ducts in different environmental conditions should consider selecting bus ducts of different types and materials.In addition,for various bus ducts,the bus duct section should usually be selected according to the long-term working current.

　　At present,most projects only have three-phase four wire or three-phase five wire current.Some projects have added IP protection levels,and important safety technologies should be clearly written on the drawings as much as possible in the design process to prevent difficulties caused by technical parameters in project settlement and reduce safety hazards.The quality control audit of production,including the inspection of conductors,whether there are instruments for measuring the resistivity of conductors in bus ducts,whether there are voltage withstand test equipment for busbars,whether there are temperature rise test equipment for the current interception capacity of bus ducts,and whether there are test equipment for protecting circuit continuity,all have a direct impact on the qualification rate of production enterprise products leaving the factory.These testing equipment are necessary to ensure that the quality assurance of the company's factory products can provide effective basis.

　　Due to factors such as the resistance of conductors and the AC current meter effect when multiple conductors approach each other,heating can occur when current passes through the bus duct.The allowable temperature for heating during long-term operation of copper and aluminum bus ducts is 70℃,but when there is a reliable coverage of tin at their contact surfaces,the temperature can be increased to 85℃.Due to the limitation of the allowable temperature for continuous heating,bus ducts of different materials and cross-sections are given corresponding long-term allowable current values.When selecting the section of the bus duct,the actual long-term operating current of the bus duct should be lower than the long-term allowable current value of the selected section of the bus duct.In situations where the average annual load is high and the conductors and bus ducts are long,the bus ducts are usually selected using the economic current density method.Economic current density refers to the current that flows through a unit cross-sectional area of a bus duct,taking into account the losses of the bus duct and the annual maintenance and depreciation costs of the bus duct and its ancillary equipment.The cross-sectional area of the bus duct is obtained by dividing the economic current density by the long-term operating current without considering overload.The cross-sectional area of the bus duct selected by the economic current density method is generally larger than that selected by the long-term working current.