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To provide a comparative and comprehensive overview for selecting different conductor cross-sectional areas, CHANGHUI INSTRUMENTS has compiled the requirements for the cross-sectional areas of phase conductors, N conductors, PE conductors, PEN conductors, protective connection conductors, and grounding conductors, for quick reference during electrical design. Requirements for the cross-sectional area of conductors: yunrun.com.cn/tech/3454.html – Summary of guidelines for selecting the cross-sectional area of conductors in low-voltage distribution circuits. 1. Technical requirements for selecting the cross-sectional area of phase conductors: ① The current-carrying capacity of the conductor should not be less than the calculated current of the circuit. ②The line voltage drop should meet the terminal voltage requirements for the normal operation and startup of electrical equipment and lighting fixtures. ③It shall meet the requirements for protection against line failures. ④It shall meet the requirements for short-circuit dynamic stability and thermal stability. ⑤The minimum cross-sectional area of the conductor shall meet the mechanical strength requirements. ⑥For circuits that supply steady loads over long periods of time, the cross-sectional area of the conductors is selected based on the economic current density. 2. Technical requirements for selecting the cross-sectional area of N conductors: ① In one of the following situations, the cross-sectional area S of the N conductors should be equal to the cross-sectional area Sph of the phase conductors: a. Single-phase two-wire systems ； b. Three-phase four-wire systems, with copper conductors of ≤16 mm2 and aluminum conductors of ≤25 mm2 ； c. The content of the third harmonic is >15%, but ≤33%. ② For three-phase four-wire systems, if all of the following conditions are met, SN can be reduced, but it must not be less than 50% of Sph: a. The copper core diameter is >16mm2, and the aluminum core diameter is >25mm2 ； b. The current in conductor N (including the current caused by harmonics) is less than its current-carrying capacity ； c. The N conductor is equipped with overcurrent protection. ③The third harmonic content being greater than 33% causes the current in the N conductor to be greater than that in the phase conductors. When the N conductor and the phase conductors have the same cross-sectional area and are located within the same cable or laid in the same conduit or trough, the cross-sectional areas of the phase conductors and the N conductor should be selected based on the current in the N conductor. 3. Technical requirements for selecting the cross-sectional area of PE conductors: ① Meet the requirement for automatic power cut-off in case of faults. ②It can withstand the mechanical and thermal stresses caused by the expected fault current during the time it takes for the protective device to disconnect. ③The cross-sectional area SPE of the PE conductor shall be selected in accordance with one of the following requirements: a, b; when Sph ≤ 16 mm²: SPE = Sph ； When Sph＞16mm2: SPE≈1/2×Sph. ④The PE conductor is not placed within the same outer protective covering as the phase conductors. The minimum cross-sectional area required for SPE is as follows: a) In the presence of mechanical protection: 2.5 mm2 for copper, 16 mm2 for aluminum ； b. Without mechanical protection: copper 4mm2, aluminum 16mm2 ； 4. Technical requirements for selecting the cross-sectional area of the PEN conductor: ① It shall meet all the functional requirements of both the PE conductor and the N conductor. ②PEN conductors cannot be installed in the terminal circuits of electrical equipment, lighting fixtures, and sockets ； It shall also not be used in environments with fire and explosion hazards. ③The cross-sectional area of the PEN conductor in fixed electrical installations shall not be less than: Copper: 10 mm2 ； Aluminum: 16mm2. ④Metal enclosures such as steel pipes and troughs used for wiring should not be used as PEN conductors. ⑤External conductive parts (such as water pipes and steel components) must not be used as PEN conductors. 5. Technical requirements for selecting the cross-sectional area of protective connection conductors: ① For protective connection conductors connected to the main grounding terminal: a) The cross-sectional area shall not be less than half of that of the largest PE conductor in the installation, and shall also be no less than: 6 mm2 for copper, 16 mm2 for aluminum, and 50 mm2 for steel. b. The cross-sectional area of the aforementioned protective bonding conductor need not exceed 25 mm2 for copper or the equivalent cross-sectional area for other materials. ②Protective bonding conductors for auxiliary bonding: a. The protective bonding conductors of the two exposed conductive parts shall have a conductivity not lower than that of the smaller PE conductor ； b. The conductive link for protecting the exposed conductive parts and external conductive parts shall have a conductivity that is not less than half of the cross-sectional area of the PE conductor ； c. The minimum cross-sectional area of the protective bonding conductor for auxiliary bonding, as well as the bonding conductor connecting the two externally conductive parts, shall meet the requirements specified for PE conductors ④. 6. Technical requirements for selecting the cross-sectional area of the grounding conductor: ① The grounding conductor shall meet the requirements regarding the cross-sectional area of the PE conductor in a TT system. ②The cross-sectional area of the grounding conductor shall not be less than: 6 mm² for copper ； Steel 50mm2. ③The cross-sectional area of the grounding conductor, which also serves as a lightning protection conductor, should not be less than: 16 mm2 for copper ； Steel 50mm2. ④Aluminum should not be used for grounding conductors. ⑤The cross-sectional area of the bare grounding conductor buried in the soil should not be less than: a) 50 mm2 for copper strips, with a thickness of not less than 2 mm ； b. Horizontally installed round copper wire of 50 mm2, used solely for shock protection; 25 mm2 may be used as well ； c. Hot-dip galvanized steel: flat steel with a cross-sectional area of 90 mm2 and a thickness of not less than 3 mm; horizontally installed round steel: diameter of 10 mm. Examples of protective conductors: To properly distinguish among the various protective conductors in a power distribution system and avoid confusion, and to accurately identify which wires belong to the PE conductor, which ones are part of the protective connection for common equipotential bonding, and which ones are part of the auxiliary equipotential bonding, graphical examples are provided. Example Figure 1 shows these; the phase conductors and the N conductor, which carry current, are not indicated in the figure. http://yunrun.com.cn/upload/202011/20/202011201535551950.png Figure 1 Example of PE conductor and protective bonding conductor (Legend: ① is the protective bonding conductor connected to the MEB (or MET)) ； ②Protection bonding conductor to assist in bonding ； ③For the grounding conductor ； D refers to electrical equipment of Class I protection against lightning strikes, connected to the grounding terminal of the device’s exposed conductive parts) Source: Changhui Instrument Network