In the electrical equipment of engineering projects,the distribution main line,which is equivalent to the main artery of ten people,occupies an extremely important position.Once the distribution main line malfunctions,it will cause all bus ducts to malfunction.When using bus ducts as distribution main lines,the protection level of the bus duct enclosure becomes very important.Bus ducts that operate in normal environments can also experience faults,which are unavoidable.One of the common faults in bus ducts is short circuits.Once a short circuit occurs and the bus duct cannot be immediately disconnected,the distribution main line will inevitably experience overload.Therefore,even distribution lines operating in normal environments must have the ability to withstand overload.

　　In practice,the ideal working environment should not be considered as a normal working environment when designing distribution lines.The so-called ideal environment refers to an environment that is dry,free from water leakage,and does not experience short circuits in the load.Obviously,such an environment does not exist.The ideal working environment,combined with the potential environmental changes that may occur in this environment,constitutes a normal environment.Even within the same building,the so-called normal environment is different.The normal humidity in the basement environment is higher than that on the ground;The normal environment of the distribution main line located next to the water pipe and in the fire sprinkler area is more susceptible to the danger of water spraying than the surrounding environment without water pipes;Individual bus duct short circuits causing overload of distribution lines are within the normal operating range of distribution lines.

　　Bus duct wiring should be installed openly in indoor dry and less susceptible to mechanical damage environments under normal conditions,but should not be used in places where the bus duct is severely corroded.All phase and neutral wires of the unified circuit should be laid in the unified bus duct.A line without anti-interference requirements for a unified path can be laid in a unified trunking,and the number of current carrying wires should not exceed 30.The lower limit of the number of wires or cables used for control,signaling,or similar circuits.When installing the bus duct vertically or obliquely,measures should be taken to prevent wires or cables from moving inside the duct.Wiring methods such as metal pipes,hard plastic pipes,semi-rigid plastic pipes,metal hoses,or cables can be used for the lines led out from the bus duct.Wires or cables must not be damaged in the outgoing section.The wire groove should be flat,without distortion or deformation,and the inner wall should be smooth and free of burrs.Bus ducts should be reliably grounded or zeroed,but cannot be used as grounding conductors for equipment.The occurrence of fires and human damage in the working environment resulting in power outages in the distribution main line is considered an abnormal working environment.When designing electrical systems,it is necessary to consider both the reliability of the distribution main line operating in normal environments and the occurrence of abnormal working environments.