Zero line configuration of phase power supply
For a switching power supply with a power factor of 0.4 - 0.6, when a multiple power supply is balanced in a three-phase four wire system, the current of the zero line can not offset due to the distortion of the input current waveform. Therefore, in general, it is recommended to set the specifications of the zero line as 1.5 to 2 times the phase line, and to configure the maximum measured current.
Why does the zero line of the three-phase four line lighting line be insure (air switch), and the single phase double line lighting circuit must be insured (air switch)?
In a system of three-phase four line 380/220 volt neutral grounding, if the zero line is insured, if the insurance is broken, if the three-phase load is not balanced on the line behind the breakpoint, a relatively high voltage will appear in a phase with less load, thus causing accidents to burn out the equipment, especially when the single phase is generated. So the zero line is not allowed to install an insurance device.
For the real 220 double line lighting power supply lines, most people are not familiar with the electrical contact, and sometimes repair and extend the line, often the line and the zero line. In addition to this line, the zero line is broken, and the accident of the burning electrical equipment is not caused, so fuse is installed on the zero line.