1. The neutral conductor should have the same cross section as the phase conductor when:

1) Single-phase two-wire circuit of any cross section;

2) In three-phase four-wire and single-phase three-wire circuits, the phase conductor cross section is not more than 16mm2 (copper) or 25mm2 (aluminum)

2. In the three-phase four-wire system, if the phase conductor cross section is larger than 16mm2 (copper) or 25mm2 (aluminum) and all of the following conditions are met, the neutral conductor cross section may be smaller than the phase conductor cross section:

1) During normal operation, the expected maximum current of the neutral conductor is not greater than the allowable current carrying capacity of the reduced neutral conductor section.

2) For TT or TN systems, where the neutral conductor cross section is smaller than the phase conductor cross section, the neutral conductor shall be provided with an overcurrent protection corresponding to the conductor cross section. This protection shall cause the phase conductor to be de-energized but not necessarily disconnected. Sexual conductor. Overcurrent protection is not required on the neutral conductor when the following two conditions are met:

——The protective device of the loop phase conductor can protect the neutral conductor;

– The maximum current that may pass through the neutral conductor during normal operation is significantly less than the current carrying capacity of the conductor.

3) The neutral conductor has a section of not less than 16 mm 2 (copper) or 25 mm 2 (aluminum).

3. The protective conductor must have a sufficient cross section, and its cross section can be determined by one of the following methods:

1) When the cutting time is between 0.1 and 5 s, the cross section of the protective conductor shall be determined as follows:

Where S is the cross-sectional area (mm2);

I——The fault current (square root mean value) at which a fault with negligible impedance occurs (A);

T——the time (s) that the protection appliance automatically cuts off the power supply;

K—depending on the material of the protective conductor, insulation and other parts, and the coefficients of the initial and final temperatures, can be calculated according to the current national standard “Selection and installation of electrical equipment, installation of conductors and protective conductors” GB16895.3 and Select.