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The standard specifications for grounding resistance require that: 1. The grounding resistance for independent lightning protection systems should be less than or equal to 10 ohms； 2. The resistance of the independent safety protection grounding system should be less than or equal to 4 ohms ； 3. The resistance of the independent communication system ground connection should be less than or equal to 4 ohms ； 4. The resistance of the independent DC operating ground connection should be less than or equal to 4 ohms ； 5. The anti-static grounding resistance is generally required to be less than or equal to 100 ohms. 6 The common grounding electrode (combined grounding) should have a grounding resistance of no more than 1 ohm. 【The ground wire of the lightning rod belongs to the grounding system for lightning protection. If both the grounding resistance of the lightning rod and that of the anti-static grounding system are set according to the requirements, then the ground wire of the anti-static equipment can be connected to the ground wire of the lightning rod. Since the grounding resistance of the lightning rod is 10 times lower than that of the anti-static grounding system, in the event of a lightning strike, most of the electrical current will be discharged through the lightning rod’s ground wire, while the current flowing through the anti-static grounding system can be considered negligible.】 There are three types of grounding: Protective grounding: This is used for the metal enclosures of electrical equipment, concrete structures, utility poles, etc. These components may become energized due to insulation damage; protective grounding is implemented to prevent such situations from posing a threat to personal safety. Below 1Ω: Anti-static grounding: Grounding of flammable fuel and natural gas storage tanks and pipelines, electronic equipment, etc., to prevent the effects of static electricity hazards. Lightning protection grounding: This is a type of grounding in which the grounding terminals of lightning protection devices (such as lightning rods) are connected to the ground, thereby diverting lightning currents into the earth. Its purpose is to eliminate the hazards posed by overvoltages caused by lightning to electrical equipment, as well as to human life and property. It is also known as overvoltage protection grounding. It should be noted that the three types of grounding must be installed separately. Identification of grounding wires: Differentiation of wire types; regulations regarding grounding electrodes; protective grounding wires; yellow-green bicolored wires. The distance between three types of grounding electrodes must be greater than 20 meters. Anti-static grounding wires are green in color. Lightning protection grounding wires utilize galvanized round steel. Grounding requirements: The grounding of AC electrical installations shall comply with the following provisions: 1. When the high-voltage side of a distribution transformer operates under a low-resistance grounding system, the grounding resistance of the protective grounding network must meet the following formula: R ≤ 2000/I (1-1). Here, R represents the maximum grounding resistance taking seasonal variations into account (in ohms) ； I――The human-ground short-circuit current (A) flowing through the grounding grid for calculation purposes. 2. When the high-voltage side of the distribution transformer operates in an ungrounded system, the grounding resistance of electrical installations shall meet the following requirements: 1) The grounding resistance of the grounding grid shared by high-voltage and low-voltage electrical installations shall satisfy the formula below, and should not exceed 4Ω: R≤120/I (1-2) 2) The grounding resistance of the grounding grid used solely for high-voltage electrical installations shall satisfy the formula below, and should not exceed 100Ω: R≤250/I (1-3) Where R represents the maximum grounding resistance considering seasonal variations (Ω) ； I—Ground fault current for calculation (A). 3. In power networks where the neutral point is grounded through arc suppression coils, when the grounding resistance of the grounding grid is calculated using formulas (1-2) and (1-3) in these specifications, the grounding fault current shall be determined as follows: 1) For the grounding grids of substations or electrical installations equipped with arc suppression coils, the calculated current shall be 1.25 times the sum of the rated currents of all arc suppression coils within the same power network and connected to the same grounding grid ； 2) For substations or electrical installations without arc-suppression coils, the calculated current shall be the maximum possible residual current when the largest arc-suppression coil in the power grid is disconnected, and shall not be less than 30A. 4. In areas with high soil resistivity, when the grounding resistance of the grounding grid reaches the specified values and it is not technically or economically feasible to meet those values, the grounding resistance of electrical installations may be increased to 30Ω, and that of the grounding grid in substations may be increased to 15Ω; however, this must comply with the requirements of Article 12.6.1 of these specifications. In low-voltage systems, the grounding resistance at the neutral point of distribution transformers should not exceed 4 Ω. In areas with high soil resistivity, where it is difficult to achieve the aforementioned ground resistance values, a grid-type grounding system can be used, provided that the requirements of Article 12.6.1 of these specifications are met. The grounding resistance of the distribution equipment shall comply with the following requirements: 1 When the distribution transformer that supplies power to a building is installed outside the building, the following rules apply: 1) For distribution transformers whose high-voltage side operates in an ungrounded, arc-suppression coil grounded, or high-resistance grounding system, if the grounding resistance of the protective grounding network of such transformer meets the requirements specified in formula (12.4.3) and is no more than 4Ω, then the grounding point of the low-voltage system supply can share the same grounding network as the transformer’s protective grounding. The grounding resistance of electrical installations shall meet the requirement given by the following formula: R ≤ 50/I (12.4.3). Here, R represents the maximum grounding resistance of the grounding grid, taking seasonal variations into account (Ω) ； I――Single-phase ground fault current ； The arc-suppression coil grounding system is for the residual current at the fault point. 2) At the point where low-voltage cables and overhead lines enter a building, in TN-S or TN-C-S systems, the protective conductor (PE) or the protective earth neutral conductor (PEN) should be grounded repeatedly, with the grounding resistance not exceeding 10Ω ； For TT systems, the protective conductor (PE) is grounded separately, and the grounding resistance should not exceed 4Ω ； 3) When the high-voltage side of the distribution transformer that supplies power to the low-voltage system operates in a low-resistance grounding system, the low-voltage system shall not share the grounding grid with the protective grounding of the power supply distribution transformer. A dedicated grounding grid should be installed at an appropriate location relative to that distribution transformer for the power connection point of the low-voltage system, and its grounding resistance should not exceed 4Ω. 2 When a distribution transformer that supplies power to a building is installed within that building, the following requirements shall be met: 1) For distribution transformers whose high-voltage side operates in an ungrounded, arc-suppression coil grounded, or high-resistance grounding system, if the grounding resistance of the grounding grid used for the protection grounding of such transformer is not greater than 4Ω, the power supply grounding point of the low-voltage system may share the same grounding grid as that used for the protection grounding of the transformer ； 2) The high-voltage side of the distribution transformer operates in a low-resistance grounding system; when the grounding resistance of the transformer’s protective grounding network meets the requirements specified in formula (1–1) of this standard, and when total equipotential bonding is employed within the building, the power supply grounding point of the low-voltage system can share the same grounding network as the transformer’s protective grounding. The lightning arrester protecting the distribution transformer should share the grounding grid with the transformer’s protective grounding. The grounding conductors of lightning arresters that protect circuit breakers, load switches, capacitor banks, and similar devices on distribution poles should be connected to the equipment’s enclosure, with the grounding resistance not exceeding 10Ω. In a TT system, when the system ground point and the exposed conductive parts of electrical equipment are connected together at the same potential, it is not necessary to install a separate grounding grid for those exposed conductive parts ； When no total equipotential bonding is implemented, a grounding network for protective earthing shall be provided for the exposed conductive parts of electrical installations; its grounding resistance must meet the requirements of the following formula. R≤50/Ia (12.4.6-1), where R is the maximum grounding resistance of the grounding grid considering seasonal variations (Ω) ； It is the operating current (A) that ensures the protection device cuts off the faulty circuit. When a residual operating current protector is used, the grounding resistance shall meet the requirement given by the following formula: R ≤ 25I△n, where I△n is the operating current of the residual operating current protector in mA, as specified in equation (12.4.6-2). The protective grounding of the exposed conductive parts of various electrical devices in IT systems can share a common grounding grid, or it can be grounded using separate grounding grids, either individually or in groups. The grounding resistance of each grounding grid shall meet the requirement given by the following formula: R ≤ 50/Id (12.4.7), where R is the maximum grounding resistance of the grounding grid, taking seasonal variations into account (Ω) ； Id – Fault current (A) during the first short-circuit fault between the phase conductor and the exposed conductive parts. The grounding of various electrical systems in a building should preferably use the same grounding grid. The grounding resistance of the grounding grid shall meet the requirement of the minimum value among them. The grounding of overhead lines and cable circuits shall comply with the following provisions: 1 In low-voltage TN systems, the PEN conductor or PE conductor at the ends of main and branch overhead lines shall be repeatedly grounded. At the incoming points of cable lines and overhead lines at each building, repeated grounding shall be provided in accordance with the provisions of Article 12.2.2 of this code. Repeated grounding is not permitted on the PEN conductor equipped with a residual current device. Except for the power supply neutral point, the neutral conductor (N) should not be grounded repeatedly. The grounding resistance of each repeated grounding grid for low-voltage lines should not exceed 10Ω. In power networks where the allowable grounding resistance of electrical equipment is 10 Ω, the grounding resistance at each repeated grounding point should not exceed 30 Ω, and there should be no fewer than 3 such repeated grounding points. 2 In residential areas with non-asphalt surfaces, the reinforced concrete poles for 10(6) kV high-voltage overhead distribution lines should be grounded; metal towers must also be grounded. The grounding resistance should not exceed 30 Ω. For low-voltage overhead lines in systems with directly grounded power supply neutral points, as well as lines with both high-voltage and low-voltage conductors on the same pole, except where residual current devices are installed at the outlet ends, the iron crossarms or poles of the reinforced concrete poles should be connected to the PEN conductor; the rebar in the reinforced concrete poles should also be connected to the PEN conductor. 3 The metal exteriors at both ends of power cables laid through metal conduits shall be grounded; the metal exteriors of power cables in substations can be grounded using the main grounding grid. When using all-plastic cables, it is advisable to lay 1–2 grounding conductors along the cable trench with both ends grounded.