3.3 Selection of busbars in the cabinet
In the normal project design, several main circuits in the low-voltage switchgear cabinet are connected to the busbar. The expected maximum current through the busbar at any time is the sum of the rated currents of all the main circuits connected to it multiplied by the rated dispersion factor (see Table 2). The specifications of the bus bar are selected according to the maximum current expected to pass. See Table 3 for the selection of the specifications of the vertical bare copper busbar of the feeder cabinet and the corresponding rated ampacity.
Table 2: Rated dispersion coefficient value (reference standard GB 7251.1-2005 Article 4.7 Table 1)
Number of main circuits
Rated dispersion coefficient
Table 3: Rated ampacity table of vertical bare copper bus（Phase spacinga=80）
3.4 Selection of other copper busbars in the device
The selection of the branch bus of the incoming line or the contact switch takes into consideration the rated current of the system and the frame current of the switch. When the rated current of the system is greater than the frame current of the switch, the branch bus selects the rated current of the frame switch; otherwise, the rated current of the system is selected. The connecting bus of other components is selected according to the frame current of the components. The selection of copper bar specifications will give priority to the use of common copper bar specifications in the K3 system. The use of uncommon copper bar specifications must be approved by the mechanical branch manager. The rated current carrying capacity of other copper busbars in the device is shown in Table 4.
Table 4: Rated ampacity table of other copper busbars in the device (design selection)
Rated current carrying capacity (A)