Ordinary bus duct is a transmission and distribution system with electrical continuity formed by wrapping several conductors in a metal shell through a reasonable and safe structure.Ordinary bus ducts are generally divided into two types:dense insulation type and air insulation type.Air insulation type has a simple structure and can transport large currents;The dense insulation structure is compact and has good heat dissipation capability.They all have the characteristics of strong overload capacity,convenient tapping,and small space occupation.

　　Cables are divided into single core cables and multi-core cables.Single core cables mainly use various insulation materials,with multiple strands of copper wire wrapped in insulation layers as a current conductor for a certain phase.A multi-core cable is a complete cable formed by twisting multiple insulated wire cores together and wrapping them with an outer sheath.The number of insulated cores in power cables is usually 1,2,3,4,5,as well as 4+1 and 3+2 cores.The main advantages of cables are flexible selection and strong environmental adaptability,but they also have inherent limitations.The cable tray is relatively large and commonly used between floors and various distribution rooms in general buildings,while the trunking is relatively small;The turning radius of the bridge is relatively large,and most of the cable trays turn at right angles;The span of the bridge is relatively large,and the cable tray is relatively small;And the fixing and installation methods are different.In some places,cable trays are uncovered,and most of the cable trays are covered and sealed.

　　The bridge 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 wire and the three-phase busbar is equal,with the same reactance.This also avoids long-term corrosion at the connection between the shell and PE.Bus duct tapping is convenient,and the so-called plug-in bus duct refers to its use of plugging to tap the power supply of the main line to the branch line,making tapping very convenient.The disadvantage of cables is that they need to be customized from the factory.The strong overload capacity of the bus duct depends on the high working temperature of the insulation material used.The insulation material used for the bus duct is made of materials with a working temperature of 105℃.Radiation cross-linked flame-retardant winding tape(PER)and radiation cross-linked hydrocarbon heat shrink tubing with a working temperature of over 140℃have been developed.The insulation material used in cables generally operates at temperatures of 95℃and 105℃,so the overload capacity of bus ducts is much greater than that of cables.

　　The outer shell of the bus duct is made of steel and will not burn.Even if the insulation material of the copper bar burns,the flames will not spread outside the bus duct.The insulation layer and outer skin of ordinary cables will burn,and flame-retardant cables will also burn under flames.They only do not burn after the flame has left,while fire-resistant cables will not burn,but they are expensive.Only fire-resistant cables are used for power supplies that are not allowed to be cut off,such as firefighting.The insulation materials of cables(core insulation and outer insulation)are both insulation materials and thermal insulation materials.Therefore,when laying power cables in cable trays,it is allowed to lay two more layers,and the reason for this is to consider heat dissipation.Bus ducts utilize air conduction for heat dissipation and dissipate heat through closely contacting metal shells.Therefore,their heat dissipation performance is average compared to cables.