There are many ground resistance values ??for electrical devices. Different systems specify different resistance values ??according to the difference in power distribution systems and the size of the ground fault current. Here is an excerpt of some of the specified values ??in the current specifications. Two of the specifications have been updated or invalidated according to the 2009 Ministry of Construction documents. But still available for reference.
(1) Signal grounding - the grounding set up to ensure that the signal has a stable reference potential.
(2) Power grounding - the working grounding of other AC and DC circuits other than electronic equipment systems.
(3) Protective grounding - grounding to ensure the safety of people and equipment.
14.7.4.3 Unless otherwise specified, the grounding resistance value of electronic equipment should generally not be greater than 4Ω and use a point grounding method. The grounding of electronic equipment should be the same as the lightning protection grounding system. However, the grounding resistance should not be greater than 1Ω at this time. If it is separated from the lightning protection grounding system, the distance between the two grounding systems should not be less than 20m. Regardless of whether a dedicated grounding system or a separate grounding system is used, the provisions related to lightning protection in Chapter 12 of this specification should be met.
Electronic equipment should decide whether to use shielding measures as needed.
(1) DC ground (including the grounding of logic and other analog signal systems).
(2) Exchange work place.
(3) Safety protection area.
The ground resistance values ??of the above three types of grounding are generally required to be no more than 4Ω. Under normal circumstances, electronic computer signal systems should not use floating grounding.
14.7.5.2 The three grounding devices of electronic computers can be set up separately.
If a special grounding method is used, the grounding resistance of the grounding system should be based on the smallest grounding resistance value among various grounding devices. If used with lightning protection grounding system, the grounding resistance value should be ≤1Ω.
Refer to the relevant provisions of Chapters 11, 12, 22 and 23 of the "Electrical Design Code for Civil Buildings" JGJ16-2008, under normal circumstances:
2) The distribution transformer is located in the building When the low-voltage cable is outside the building, the low-voltage cable is introduced into the building. For TN-S or TN-C-S systems, PE wire or SE_hldp01350_v6v6zkg6" target="_blank" rel="nofollow" data-word="4">The grounding should be repeated, and the grounding resistance should not exceed 10Ω; for the TT system, the PE line should be grounded separately, and the grounding resistance should not exceed 4Ω;
3) For the second and third For lightning protection buildings, when artificial lightning protection down conductors are used (this situation is extremely rare), the impact resistance of each down conductor should not be greater than 10Ω and 30Ω respectively; when natural lightning protection down conductors are used, the impact resistance of each down conductor should not be greater than The impulse resistance value of the line does not need to be specified;
4) Unless otherwise specified, the grounding resistance value of electronic, information and computer equipment should not be greater than 4Ω;
5) When using ** *When using the grounding method, the grounding resistance should be based on the minimum value of the grounding resistance required in various grounding systems. Unless otherwise specified, when a grounding body is used for various grounding systems and lightning protection grounding systems, the grounding resistance value should not be greater than 1Ω.
Special attention should also be paid to: To determine the presence or absence of electronic, information and computer equipment in a building, the presence or absence of equipment rooms and host equipment is generally used as an important indicator of measurement.
11.0.4 When the integrated wiring system adopts shielding measures, it must have a good grounding system and comply with the following regulations:
1 The grounding resistance value of the protective ground wire must be set separately. When a grounding body is used, it should not be greater than 4Ω. When a joint grounding body is used, it should not be greater than 1Ω.
2 When using a shielded wiring system, all shielding layers should maintain continuity.
3 When using a shielded wiring system, the wiring device (FD or BD) end of the shielding layer must be well grounded. The user (terminal equipment) end should be grounded depending on the specific situation. The grounding at both ends should be connected to the same ground. body. If there are two different grounding bodies in the grounding system, the grounding potential difference should not be greater than 1Vr.m.s.
7.0.3 Floor or local equipotential grounding should be set up in telecommunications rooms, equipment rooms and incoming wire rooms0">. The integrated wiring system should adopt a grounding system with special grounding. If a separate grounding body is installed, the grounding resistance should not be greater than 4Ω. If there are two different grounding bodies in the grounding system of the wiring system, the grounding potential difference should not be greater than 1Vr.m.s.
7.0.5 Each wiring cabinet (rack, box) installed on the floor should be individually routed to the nearest equipotential grounding device using insulated copper wires of appropriate cross-section, or 9">The internal equipotential grounding copper bar is led to the building's grounding device. The cross-section of the copper conductor should be Meet design requirements.
7.0.6 At the junction of cables in the lightning protection zone, both ends of the shielding layer of the shielded cable should be equipotentially connected and grounded.
2.9.2 A lightning rod should be installed on the vertical pole (stand) of the receiving antenna. The height of the lightning rod should be sufficient to protect the antenna facilities. When installing an independent lightning rod, the minimum horizontal distance between the lightning rod and the antenna should be greater than 3m.
2.9.3 Both the independent lightning rod and the vertical pole of the receiving antenna should be reliably grounded. When the building has a lightning protection grounding system, the grounding of the lightning rod and the antenna pole should be firmly connected to the building's lightning protection grounding system; when the building does not have a special lightning protection grounding system available, a special lightning protection grounding system should be set up. For the grounding device, two down-leads from the air-termination device to the grounding device should be used, and they should be led down along the building at the shortest distance from different directions; the grounding resistance should not be greater than 4Ω.
2.5.3 The system should be grounded at one point. The grounding bus should be made of copper wire. The grounding wire must not form a closed loop, and must not be short-circuited or mixed-connected with the strong neutral line of the power grid.
2.5.4 When the system uses a special grounding device, its grounding resistance shall not be greater than 4Ω; when a comprehensive grounding network is used, its grounding resistance shall not be greater than 1Ω.
The lightning protection grounding device should be connected to the grounding device of electrical equipment and buried metal pipes. When not connected, the distance between the two should not be less than 20m.
Article 6.3.7. The electrostatic grounding can be connected to the grounding device through a current-limiting resistor and its own connecting wire. The resistance of the current-limiting resistor should be
Article 6.4.1 The setting of the grounding device in the electronic computer room should meet the safety requirements for personal safety and the normal operation of the electronic computer and system equipment. ?
If the technical specifications for detection of lightning protection devices in flammable and explosive places have special provisions on the value of electrostatic grounding resistance, these provisions shall be followed; when indirect electrostatic grounding is adopted, the grounding resistance should not be greater than 1MΩ.
5.2.3 The grounding device used for *** should be connected to the main equipotential grounding terminal board, lead to the floor equipotential grounding terminal board through the grounding trunk line, and then lead to the local equipotential grounding terminal in the equipment room plate. The local equipotential grounding terminal board should be connected to the reserved grounding terminal of the main steel bar on the floor. The grounding trunk line should use multi-stranded copper core wires or copper strips, and its cross-sectional area should not be less than 16mm2. The grounding trunk line should be laid openly in the electrical shaft and should be connected to the main steel bars of the floor for equipotential connection.
5.2.4 Local equipotential grounding terminal boards should be installed in the integrated wiring system equipment rooms on different floors or in the wiring transfer rooms in different lightning protection areas. The grounding wire of the floor wiring cabinet should be an insulated copper wire with a cross-sectional area of ??not less than 16mm2.
5.2.5 Lightning protection grounding, AC working grounding, DC working grounding, and safety protection grounding*** When using a set of grounding devices, the grounding resistance value of the grounding device must be the minimum required in the access equipment. The value is determined.
5.2.6 The grounding device should give priority to the natural grounding body of the building. When the grounding resistance of the natural grounding body cannot meet the requirements, an artificial grounding body should be added.
5.2.7 When an artificial grounding body is set up, the artificial grounding body should be buried in a ring-shaped grounding body more than 1m away from the water slope around the building, and can be used as a general equipotential bonding zone.
Article 3.1.1 Factory (mining) area telephone switches, carriers, dispatch telephone switchboards, conference telephone tandem machines or terminals, cable broadcast amplifiers, production amplifiers, etc. that do not use the earth as a signal loop The resistance value of the grounding device of communication equipment should comply with the following regulations:
2. The grounding resistance value of AC power supply or AC-DC dual-purpose communication equipment, when the AC single-phase load of the equipment is less than or equal to 0.5 kVA When it is greater than 0.5 kVA, it should not be greater than 4 ohms.
Article 3.1.2 The grounding resistance value of the two sets of grounding bodies connected in parallel for the telephone exchange in the factory (mine) area that uses the earth as the signal loop should not be greater than the requirements in Table 3.1.2.
Grounding resistance table 3.1.2 of telephone exchanges that use the earth as a signal loop
≤600
Article 3.1.3 When the grounding of the telecommunications station complies with Article 3.1.2. When specified in Article 2.1.3, the resistance value of the grounding device shall comply with both the grounding resistance value of the telecommunications station and the provisions on the neutral point grounding resistance value of the AC power supply transformer in the national "Grounding Design Code for Industrial and Civil Power Installations".
Article 3.1.4 The grounding resistance value of the general grounding bar that complies with the provisions of Article 2.1.4 should not be greater than 1 ohm.
5.3.1 The working grounding resistance of power transformers or generators with a single capacity exceeding 100kVA or operating in parallel using the same grounding device and with a total capacity exceeding 100kVA shall not be greater than 4Ω.
The working grounding resistance of power transformers or generators with a single capacity not exceeding 100kVA or operating in parallel using the same grounding device and with a total capacity not exceeding 100kVA shall not be greater than 10Ω.
In areas where the soil resistivity is greater than 1000Ω·m, when it is difficult to achieve the above grounding resistance value, the working grounding resistance value can be increased to 30Ω.
5.3.2 In addition to repeated grounding at the power distribution room or main distribution box, the protective neutral line in the TN system must also be repeatedly grounded at the middle and end of the distribution system.
In the TN system, the grounding resistance value of the repeated grounding device at each point of the protective neutral line should not be greater than 10Ω. In power systems where the working ground resistance value is allowed to reach 10Ω, the equivalent resistance value of all repeated groundings should not be greater than 10Ω.
5.3.3
5.3.4 The grounding wire of each grounding device should use 2 or more conductors, and be electrically connected to the grounding body at different points.
Aluminum conductors shall not be used as grounding bodies or underground grounding wires. The vertical ground body should be made of angle steel, steel pipe or smooth round steel, and rebar should not be used.
Grounding can use natural grounding body, but its electrical connection and thermal stability should be ensured.
5.4.6 The impact grounding resistance value of all lightning protection devices at the construction site shall not be greater than 30Ω.
5.4.7 For electrical equipment on lightning protection grounding machinery, the connected PE wires must be repeatedly grounded at the same time. Repeated grounding of the same mechanical electrical equipment and mechanical lightning protection grounding can** *Use the same grounding body, but the grounding resistance should meet the requirements for repeated grounding resistance values.
Article 4.2.1 The grounding resistance of the grounding device of low-voltage power equipment should not exceed 4 ohms. When the total capacity of generators, transformers and other electrical equipment operating in parallel using the same grounding device does not exceed 100 kVA, the grounding resistance should not be greater than 10 ohms.
Article 4.2.2 In a low-voltage power network where the neutral point is directly grounded, when using zero connection protection, the neutral line should be grounded at the power source, except for mobile power supply equipment. The neutral line should be grounded repeatedly at the terminals of trunk lines and branch lines of overhead lines and every 1 kilometer along the line. When cables and overhead lines are introduced into workshops or large buildings, the neutral line should be grounded repeatedly (except those that are not more than 50 meters away from the grounding point). If the power distribution panel or control panel in the house has a grounding device, the neutral line can also be directly connected to the ground. Connect to grounding device.
The grounding resistance of each repeated grounding device on the neutral line of the low-voltage line should not be greater than 10 ohms. In a power network where the grounding resistance of the grounding device of power equipment is allowed to reach 10 ohms, the grounding resistance of each repeated grounding device should not exceed 30 ohms, but the repeated grounding should not be less than three. For repeated grounding of the neutral line, natural grounding should be fully utilized.
Article 4.2.3 The repeated grounding of the neutral line in the DC power network should use an artificial grounding body and shall not be connected to underground metal pipes. If there is no insulation isolation device, the distance between each other should not be less than 1 rice.
5 A
Grounding resistance of electrical equipment
This standard specifies the power generation, transformation, transmission and distribution of AC nominal voltage 500kV and below. Grounding requirements and methods for electrical installations (including accessory DC electrical installations, referred to as Class A electrical installations) and building electrical installations (referred to as Class B electrical installations).
5.1.1 The grounding resistance requirements for protective grounding of electrical devices in power plants and substations are as follows.
The grounding resistance of the protective grounding of electrical devices in power plants and substations in effective grounding and low-resistance grounding systems should meet the following requirements:
(5)
The calculation in formula (5) uses the short-circuit current flowing through the grounding device into the ground. When the internal and external short-circuit of the grounding device is short-circuited, the maximum value of the symmetrical component of the short-circuit current flowing into the ground through the grounding device is used. The current should be based on 5 to 10 years. The maximum operating mode of the developed system is determined, and the short-circuit current distribution between the grounded neutral points in the system and the grounded short-circuit current distributed in the lightning protection line should be considered.
When the grounding resistance of the grounding device does not meet the requirements of equation (5), the grounding resistance can be increased through technical and economic comparison, but it shall not be greater than 5Ω, and it shall comply with the requirements of 6.2.2 of this standard.
The grounding resistance of the protective grounding of electrical equipment in power plants and substations in ungrounded, arc suppression coil grounding and high resistance grounding systems should meet the following requirements:
High voltage and power plants, The grounding device used for the low-voltage electrical equipment used for power production in the substation should comply with the following formula
(6)
In the arc suppression coil grounding system, the ground fault current used for calculation The following values ??should be adopted: ① For the grounding device of the electrical equipment of power plants and substations equipped with arc-extinguishing coils, the calculated current is equal to 1.25 times the sum of the rated currents of the arc-extinguishing coils of the same system connected to the same grounding device. ② For the grounding device of electrical equipment in power plants and substations without arc suppression coils, the calculated current is equal to the maximum possible residual current value when the largest arc suppression coil in the system is disconnected or the longest line in the system is cut off.
The grounding resistance in areas with high soil resistivity should not be greater than 30Ω, and should comply with the requirements of 3.4 of this standard.
5.1.2 Grounding resistance of lightning protection grounding of electrical equipment in power plants and substations:
Grounding resistance of independent lightning rods (including structures with independent lightning protection wires suspended).
In areas where the soil resistivity is not greater than 500Ω·m, it should not be greater than 10Ω; in areas with high soil resistivity, the ground resistance should comply with the requirements of DL/T 620-1997 "Overvoltage Protection and Insulation Coordination of AC Electrical Devices".
The grounding resistance of the lightning rods and wires on the transformer gate structure should comply with the requirements of DL/T 620-1997 "Overvoltage Protection and Insulation Coordination of AC Electrical Devices".
5.1.3 All buildings (structures) with explosion hazards in power plants and substations that may affect the main equipment in power plants and substations or seriously affect power generation and power supply, lightning protection induction grounding The resistance should not be greater than 30Ω.
5.1.4 The grounding resistance of the anti-static grounding of flammable oil and natural gas facilities in power plants should not be greater than 30Ω.
5.2.1 The grounding resistance of the protective grounding of overhead line poles and towers should not be greater than 30Ω.
5.2.2 The grounding resistance of the lightning protection grounding of overhead lines should comply with the requirements of DL/T 620-1997 "Overvoltage Protection and Insulation Coordination of AC Electrical Installations".
5.3.1 For distribution electrical devices that work in ungrounded, arc-extinguishing coil grounded and high-resistance grounding systems and supply power to building electrical devices (Class B electrical devices), the ground resistance of their protective grounding should be Comply with the following requirements:
A grounding device for use with the power grounding point of a Class B electrical installation system.
When the distribution transformer is installed outside the building that supplies power, it should meet the requirements of the following formula:
R≤50/I (8)
——The single-phase ground fault current used for calculation; the arc suppression coil grounding system is the residual current at the fault point.
When a distribution transformer is installed in a building that supplies power, it should not be greater than 4Ω.
Non-purpose grounding devices should meet the requirements of formula (7), but should not be greater than 10Ω.
5.3.2 The grounding resistance of the protective grounding of the distribution electrical device of the low-resistance grounding system shall comply with the requirements of formula (5) of this standard.
5.3.3 The grounding of the lightning arrester that protects the distribution transformer should be the same as the protective grounding of the transformer.
5.3.4 The grounding wire of the lightning arrester protecting the circuit breaker, load switch and capacitor bank on the distribution column should be connected to the equipment shell, and the grounding resistance of the grounding device should not be greater than 10Ω.
7.2.1 When the distribution transformer supplying power to Class B electrical installations is installed outside the building, the grounding resistance of the low-voltage system power supply grounding point shall meet the following requirements:
Power distribution The high-voltage side of the transformer works in an ungrounded, arc-extinguishing coil grounded and high-resistance grounding system. When the grounding resistance of the protective grounding device of the transformer meets the requirements of formula (8) and does not exceed 4Ω, the low-voltage system power supply grounding point can be connected to the transformer. Protective grounding is a grounding device.
When there is no general equipotential bonding in the building and the distance between the building and the low-voltage system power supply grounding point exceeds 50m, when the low-voltage cables and overhead lines are introduced into the building, the protective wire (PE) or The protective neutral line (PEN) should be grounded repeatedly, and the grounding resistance should not exceed 10Ω.
When the high-voltage side of the distribution transformer that supplies power to the low-voltage system works in a low-resistance grounding system, the low-voltage system shall not use a grounding device with the protective grounding of the power distribution transformer, and the power supply grounding point of the low-voltage system shall be Set up a special grounding device at an appropriate location away from the distribution transformer, and its grounding resistance should not exceed 4Ω.
7.2.2 When the distribution transformer supplying power to Class B electrical installations is installed in the building, the grounding resistance of the low-voltage system power supply grounding point shall meet the following requirements:
Power distribution The high-voltage side of the transformer works in an ungrounded, arc-extinguishing coil grounded and high-resistance grounding system. When the grounding resistance of the grounding device for protective grounding of the transformer meets the requirements of 5.3.1 of this standard, the power grounding point of the low-voltage system can be connected to the protective grounding of the transformer* **Use grounding device.
The high-voltage side of the distribution transformer works in a low-resistance grounding system. When the grounding resistance of the protective grounding device of the transformer meets the requirements of formula (5) and is used in the building (including building steel bars) When the total equipotential bonding is performed, the grounding point of the low-voltage system power supply can be connected to the protective grounding of the transformer using a grounding device.
7.2.3 When the low-voltage system is powered by a separate low-voltage power supply, the grounding resistance of the grounding device at the power supply grounding point should not exceed 4Ω.
7.2.3 When the low-voltage system is powered by a separate low-voltage power supply, the grounding resistance of the grounding device at the power supply grounding point should not exceed 4Ω.
1—Protective wire; 2—General equipotential bonding wire; 3—Ground wire; 4—Auxiliary equipotential bonding wire;
B—General equipotential bonding (grounding) terminal board; M—exposed conductive part; C—external conductive part of the device; P—metal water pipe trunk line; T—ground electrode
7.2.4 In the system, when the system ground point and the exposed conductive part of the electrical device have been combined During equipotential bonding, no additional grounding device shall be provided for the exposed conductive parts of the electrical device. Otherwise, the exposed conductive part of the electrical device should be equipped with a protective grounding device, and its grounding resistance should meet the requirements of the following formula
R≤50/Ia ?(13)
?Ia—— The operating current to ensure that the protective appliance cuts off the fault circuit, A.
7.2.5 The grounding device for protective grounding of the exposed conductive parts of each electrical device in the system can use the same grounding device, or it can be grounded individually or in groups with separate grounding devices. The grounding resistance of each grounding device should meet the requirements of the following formula
R≤50/Id (14)
?Id——The first short-circuit fault between the phase line and the exposed conductive part fault current, A.
When ground fault protection is adopted for Category 7.2.6 electrical installations, the electrical installations in the building shall adopt total equipotential bonding. The following conductive parts should be reliably connected to each other using main equipotential bonding wires, and connected to the main equipotential bonding terminal board when entering the building (Figure 6):
Water pipes, gas pipes, Metal pipes such as heating and air-conditioning pipes;
7.2.7 The insulator pins connecting household wires should be grounded, and the grounding resistance should not exceed 30Ω. For iron cross-arm reinforced concrete pole lines in areas where the soil resistivity is 200Ω·m and below, artificial grounding devices are not required. When the insulator iron leg is connected to the grounding device of the electrical installation in the building, no additional grounding device is required. For household wiring in densely populated public places, when the natural grounding resistance of the reinforced concrete pole is greater than 30Ω, the iron feet of the insulator should be grounded, and a special grounding device should be installed.
In areas where the annual average number of thunderstorm days does not exceed 30, where low-voltage lines are shielded by buildings, etc., or where the connection line is not more than 50m away from the low-voltage line grounding point, the insulator iron feet do not need to be grounded.
7.2.8 The grounding point of the low-voltage system power supply in the building, the protective grounding of the exposed conductive parts of the electrical installation (including the protective grounding used for functional grounding), the grounding electrode of the total equipotential bonding, etc. The same grounding device can be used as the lightning protection grounding of the building. The grounding resistance of the grounding device should meet the minimum value requirements.
The non-effective grounding system should be a high-resistance grounding system, with a resistance of about 1,000 ohms or more. Our common TN and TT systems are effective grounding systems, and the grounding resistance is generally between 1 and 10. There are detailed regulations in the Ministry of Electric Power's grounding system design specifications, and the number starts with DL.
For the grounding resistance value of the signal ground of electronic equipment, the relevant IEC standards and the national standards that are equivalent or equivalent to the IEC standard do not stipulate the grounding resistance value. As long as high-frequency low-impedance grounding is achieved (not necessarily connected Earth) and equipotential connection. When jointly grounded with other grounding systems, the minimum value of the grounding resistance of other grounding systems shall be determined.