What is the impedance of national standard electronic equipment to ground?

There are many grounding resistance values of electrical equipment, and different systems stipulate different resistance values according to different distribution systems and the magnitude of grounding fault current. This paper extracts some specified values in the current code. Two of them have been updated or invalidated according to the documents of Ministry of Construction in 2009. But you can still refer to it.

(1) signal grounding-grounding setting to ensure the signal has a stable reference potential.

(2) Power grounding-working grounding of other AC and DC circuits except electronic equipment system.

(3) Protective grounding-grounding to ensure personal and equipment safety.

14.7.4.3 Unless otherwise specified, the grounding resistance value of electronic equipment should generally not be greater than 4Ω, and a little grounding method should be adopted. Grounding body is applied to electronic equipment grounding and lightning protection grounding system. But the grounding resistance should not be greater than 1ω. If separated from the lightning protection grounding system, the distance between the two grounding systems should not be less than 20m. Whether using * * * grounding system or single grounding system, it shall meet the relevant provisions on lightning protection in Chapter 12 of this specification.

Electronic equipment should decide whether to take shielding measures according to needs.

(1) DC grounding (including grounding of logic and other analog signal systems).

(2) Exchange workplaces.

(3) Safety protection.

The grounding resistance of the above three kinds of grounding is generally required to be no more than 4Ω. In general, the signal system of electronic computer should not adopt floating grounding.

14.7.5.2 The three grounding devices of the electronic computer can be set separately.

If * * * grounding mode is adopted, the grounding resistance of its grounding system shall be based on the smallest grounding resistance among various grounding devices. If it is used with lightning protection grounding system, the grounding resistance shall be ≤ 1ω.

Referring to the relevant provisions in Chapters 1 1, 12, 22 and 23 of Code for Electrical Design of Civil Buildings, in general:

2) When the distribution transformer is located outside the building, the low-voltage cable is introduced into the building. For TN-S or TN-C-S systems, PE line or

3) For the second and third lightning protection buildings, when artificial lightning protection downlead is specially used (which is rare), the impact resistance of each downlead should not be greater than 10ω and 30ω respectively; When natural lightning protection downlead is used, the impact resistance value of each downlead may not be specified;

4) Unless otherwise specified, the grounding resistance value of electronic, information and computer equipment shall not be greater than 4Ω;

5) When * * * grounding mode is adopted, its grounding resistance should be based on the minimum value required in various grounding systems. Unless otherwise specified, when the grounding body is used in various grounding systems and lightning protection grounding systems, the grounding resistance value should not be greater than 1ω.

In addition, it is important to note that the existence of electronic, information and computer equipment in a building is generally judged by the existence of its computer room and host equipment.

1 1.0.4 When shielding measures are adopted for the integrated wiring system, there must be a good grounding system and the following requirements shall be met:

1 The grounding resistance value of the protective ground wire should not be greater than 4 Ω when the grounding body is set separately, and it should not be greater than1Ω when the combined grounding body is used.

When using shielded wiring system, all shielding layers should be continuous.

3 When the shielded wiring system is adopted, the wiring equipment (FD or BD) end of the shielding layer must be well grounded, and the user (terminal equipment) end should be grounded according to the specific situation, and the grounding at both ends should be connected to the same grounding body. If there are two different grounding bodies in the grounding system, the grounding potential difference should not be greater than1vr.m.s.

7.0.3 The ground or local equipotential grounding shall be set in the telecommunication room, equipment room and incoming line room.

7.0.5 Each wiring cabinet (frame, box) installed on the floor shall be individually connected to the nearest equipotential grounding device through insulated copper wire with appropriate section, or

7.0.6 Cable shall be at the joint of lightning protection belt, and both ends of shielding layer of shielded cable shall be equipotentially connected and grounded.

2.9.2 The lightning rod shall be installed on the vertical rod (frame) of the receiving antenna. The height of lightning rod should meet the protection of 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 Independent lightning rod and vertical rod of receiving antenna shall be reliably grounded. When the building has a lightning protection grounding system, the grounding of lightning rods and antenna poles should be connected with the lightning protection grounding system of the building; When there is no special lightning protection grounding in the building, a special grounding device should be set up, and two down leads from lightning arrester to grounding device should be used to lead down from different directions along the building in the shortest distance; Its grounding resistance should not be greater than 4ω.

2.5.3 The grounding of the system should adopt one-point grounding method. The grounding bus shall be made of copper wire. The grounding wire shall not form a closed loop, and shall not be short-circuited or mixed with the zero line of the strong power grid.

2.5.4 When the system adopts special grounding device, its grounding resistance should not be greater than 4Ω; When a comprehensive grounding grid is used, its grounding resistance should not be greater than 1ω.

Lightning protection grounding device should be connected with electrical equipment grounding device and buried metal pipeline. When they are not connected, the distance between them should not be less than 20m.

Article 6.3.7. Electrostatic grounding can be connected to grounding device through current limiting resistor and its own connecting wire. The resistance value of the current limiting resistor shall be

Article 6.4. 1 The grounding device of the computer room shall meet the requirements of personal safety, normal operation of computers and safety of system equipment. ?

If the Technical Specification for Detection of Lightning Protection Devices in Flammable and Explosive Places has special provisions on electrostatic grounding resistance, those provisions shall prevail; When indirect electrostatic grounding is used, its grounding resistance should not be greater than 1mω.

5.2.3 *** The grounding device shall be connected with the general equipotential grounding terminal board, and led to the equipotential grounding terminal board on the floor through the grounding trunk line, and then to the local equipotential grounding terminal board in the machine room. The local equipotential grounding terminal board shall be connected with the reserved floor main reinforcement grounding terminal. Multi-stranded copper conductor or copper tape shall be adopted for the grounding trunk line, and its cross-sectional area shall not be less than 16mm2. The grounding trunk line shall be exposed in the electrical shaft and equipotentially connected with the main reinforcement of the floor.

5.2.4 Local equipotential grounding terminal boards should be set between the integrated wiring system equipment on different floors or between the wiring handover rooms in different lightning protection areas. The grounding wire of the floor junction box shall be insulated copper wire with a cross-sectional area of not less than 16mm2.

5.2.5 When a grounding device is used for lightning protection grounding, AC working grounding, DC working grounding and safety protection grounding, the grounding resistance value of the grounding device must be determined according to the minimum value required in the access equipment.

5.2.6 The grounding device should be based on 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 installing the artificial grounding body, it should be buried in the ring grounding body larger than 1m outside the aproll around the building, and can be used as the total equipotential connection zone.

Article 3. 1. 1 The resistance value of the grounding device of the telephone exchange, carrier, dispatching telephone switchboard, conference telephone tandem machine or terminal, cable broadcast amplifier, production amplifier and other communication equipment in the factory (mine) area that does not use the earth as the signal loop shall meet the following requirements:

Second, when the AC single-phase load of the equipment is less than or equal to 0.5kVA, the grounding resistance value of the AC power supply or AC /DC dual-purpose communication equipment should not be greater than10 Ω; 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 two groups of grounding bodies connected in parallel in the telephone exchange in the factory (mine) area with the earth as the signal loop shall not be greater than the provisions in Table 3. 1.2.

Table 3. 1.2 Grounding resistance of telephone exchange using earth as signal loop.

≤600

Article 3. 1.3 When the grounding of the telecommunication station meets the provisions of Article 2. 1.3, the resistance value of the grounding device shall meet the requirements of the national Code for Grounding Design of Industrial and Civil Power Devices for the grounding resistance value of the telecommunication station and the neutral point grounding resistance value of the AC power transformer.

Article 3. 1.4 The grounding resistance of the total grounding rod conforming to Article 2. 1.4 shall not be greater than 1ω.

5.3. 1 When a power transformer or generator with a single capacity exceeding 100kVA or a total capacity exceeding 100kVA runs in parallel with the same grounding device, its working grounding resistance value should not be greater than 4 Ω.

The working grounding resistance value of a power transformer or generator whose single capacity does not exceed 100kVA or whose total capacity does not exceed 100kVA when using the same grounding device in parallel shall not be greater than 10ω.

In areas where the soil resistivity is greater than1000Ω m, the working grounding resistance can be increased to 30Ω when it is difficult to reach the above grounding resistance.

The protective zero line in line in TN system must be repeatedly grounded at the middle and end of the distribution system in addition to the distribution room or main distribution box.

In TN system, the grounding resistance value of each repeated grounding device protecting the zero line should not be greater than10Ω. In the power system that allows the working grounding resistance to reach10Ω, the equivalent resistance of all repeated grounding should not be greater than10Ω.

5.3.3

5.3.4 The grounding wire of each grounding device shall adopt two or more wires and be electrically connected with the grounding body at different points.

Aluminum conductor shall not be used as grounding body or underground grounding wire. The vertical grounding body shall be angle steel, steel pipe or smooth round steel, and rebar shall not be used.

Natural grounding body can be used for grounding, but its electrical connection and thermal stability should be guaranteed.

5.4.6 The impulse grounding resistance of all lightning protection devices on the construction site shall not be greater than 30Ω.

5.4.7 Electrical equipment on lightning protection and grounding machinery, and the PE line connected to it must be grounded repeatedly at the same time. Repeated grounding of the same mechanical and electrical equipment and lightning protection grounding of machinery can use the same grounding body, but the grounding resistance should meet the requirements of repeated grounding resistance.

Article 4.2. 1 The grounding resistance of the grounding device of low-voltage power equipment shall not exceed 4 ohms. When the total capacity of generators, transformers and other power equipment running in parallel with the same grounding device does not exceed 100 KVA, the grounding resistance should not be greater than10 Ω.

Article 4.2.2 In the low-voltage power grid with neutral point directly grounded, when zero protection is adopted, the zero line should be grounded at the power supply, except for mobile power supply equipment. At the terminals of trunk lines and branch lines of overhead lines and every 1 km along the line, the zero line shall be repeatedly grounded. When cables and overhead lines are introduced into workshops or large buildings, the zero line should be repeatedly grounded (except for those that are not more than 50 meters away from the grounding point). If the indoor switchboard and control panel have grounding devices, the neutral wire can also be directly connected to the grounding devices.

The grounding resistance of each repeated grounding device of the zero line of the low-voltage line shall not be greater than10Ω. In the power grid where the grounding resistance of power equipment grounding devices is allowed to reach10Ω, the grounding resistance of each repeated grounding device should not exceed 30Ω, but there should be no less than three repeated grounding devices. The repeated grounding of zero line should make full use of natural grounding body.

Article 4.2.3 In the DC power grid, the repeated grounding of the zero line should adopt artificial grounding body, and should not be connected with underground metal pipes and other metals. If there is no insulation isolation device, the distance between them should not be less than 1 m.

5 A

Grounding resistance of similar electrical equipment

This standard specifies the grounding requirements and methods of power generation, substation, transmission and distribution electrical devices (including auxiliary DC electrical devices, referred to as Class A electrical devices) and building electrical devices (referred to as Class B electrical devices) with a nominal AC voltage of 500kV and below.

5. 1. 1 The grounding resistance requirements for protective grounding of electrical devices in power plants and substations are as follows.

Grounding resistance of protective grounding of electrical devices in power plants and substations in effective grounding and low resistance grounding systems shall meet the following requirements:

(5)

In formula (5), the short-circuit current flowing through the grounding device is calculated by using the maximum symmetrical component of the maximum short-circuit current flowing into the earth through the grounding device when the grounding device is short-circuited inside and outside. The current should be determined according to the maximum operation mode of the system after 5 ~ 10 years, and the short-circuit current distribution between grounding neutral points in the system and the short-circuit current separated from the lightning conductor should be considered.

When the grounding resistance of grounding device does not meet the requirements of formula (5), through technical and economic comparison, the grounding resistance can be increased, but it should not be greater than 5 Ω, and it should meet the requirements of 6.2.2 of this standard.

In ungrounded, arc suppression coil grounding and high resistance grounding systems, the grounding resistance of protective grounding of electrical devices in power plants and substations shall meet the following requirements:

Grounding devices of high-voltage and low-voltage electrical devices used for power production in power plants and substations shall conform to the following formula.

(6)

In the arc suppression coil grounding system, the calculation of grounding fault current should adopt the following values: ① For the grounding devices of power plants and substations equipped with arc suppression coils, the calculated current is equal to 1.25 times of the sum of the rated currents of all arc suppression coils connected to the same grounding device in the same system. ② For grounding devices of electrical devices in power plants and substations without arc suppression coils, the calculated current is equal to the maximum residual current that may be generated 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 30 Ω, and should meet the requirements of 3.4 of this standard.

5. 1.2 grounding resistance for lightning protection grounding of electrical devices in power plants and substations:

Grounding resistance of independent lightning rod (including the structure of suspended independent lightning rod). In the area where the soil resistivity is not more than 500ω·m, it should not be more than10ω; In areas with high soil resistivity, the grounding resistance should meet the requirements of DL/ T 620— 1997 "Overvoltage Protection and Insulation Coordination of AC Electrical Devices".

The grounding resistance of lightning rod and conductor on transformer door structure shall meet the requirements of DL/T 620-1997 "Overvoltage Protection and Insulation Coordination of AC Electrical Equipment".

5. 1.3 All buildings (structures) that may affect the main equipment in power plants and substations or seriously affect power generation and power supply in power plants and substations with explosion hazards shall have grounding resistance against lightning induction not greater than 30Ω.

5. 1.4 The grounding resistance of anti-static grounding of combustible oil and gas facilities in power plant should not be greater than 30Ω.

5.2. 1 The grounding resistance of overhead line tower protection grounding shall not be greater than 30Ω.

5.2.2 The grounding resistance of lightning protection grounding of overhead lines shall meet the requirements of DL/T 620-1997 Overvoltage Protection and Insulation Coordination of AC Electrical Devices.

5.3. 1 Work in ungrounded, arc suppression coil grounded and high resistance grounded systems to supply power to building electrical devices (Class B electrical devices). The grounding resistance of its protective grounding shall meet the following requirements:

Grounding device for power supply grounding point of Class B electrical device system.

When the distribution transformer is installed outside the building it supplies, it shall meet the requirements of the following formula:

R≤50/I (8)

-Single-phase earth fault current for calculation; The grounding system of arc suppression coil is the residual current at the fault point.

When the distribution transformer is installed in the building supplied by it, it should not be greater than 4Ω.

Grounding devices not used in * * * shall meet the requirements of formula (7), but shall not be greater than10Ω.

5.3.2 The grounding resistance of protective grounding of distribution electrical devices with low resistance grounding system shall meet the requirements of Formula (5) in this standard.

5.3.3 The grounding of lightning arrester protecting distribution transformer shall be connected with transformer protection grounding device.

5.3.4 The grounding wires of lightning arresters such as circuit breakers, load switches and capacitor banks on the protection distribution column should be connected to the equipment shell, and the grounding resistance of grounding devices should not be greater than10Ω.

7.2. 1 When the distribution transformer supplying power to Class B electrical devices is installed outside the building, the grounding resistance of the power grounding point of the low-voltage system shall meet the following requirements:

The high voltage side of distribution transformer works in ungrounded, arc suppression coil grounded and high resistance grounded systems. When the grounding resistance of the protective grounding device of the transformer meets the requirements of formula (8) and does not exceed 4Ω, the power grounding point of the low-voltage system can be connected with the protective grounding device of the transformer.

When there is no total equipotential connection in the building, and the distance between the building and the grounding point of the low-voltage system power supply is more than 50m, the protective wire (PE) or protective neutral wire (PEN) shall be used for repeated grounding where the low-voltage cables and overhead lines are introduced into the building, and the grounding resistance shall not exceed10Ω.

When the high-voltage side of the distribution transformer supplying power to the low-voltage system works in a low-resistance grounding system, the low-voltage system shall not be grounded by the protective grounding of the distribution transformer, and the power grounding point of the low-voltage system shall be provided with a special grounding device at an appropriate position far away from the distribution transformer, and its grounding resistance shall not exceed 4 Ω.

7.2.2 When the distribution transformer supplying power to Class B electrical equipment is installed in the building, the grounding resistance of the power grounding point of the low-voltage system shall meet the following requirements:

The high voltage side of distribution transformer works in ungrounded, arc suppression coil grounded and high resistance grounded systems. When the grounding resistance of grounding device for transformer protective grounding meets the requirements of 5.3. 1 of this standard, the power supply grounding point of low-voltage system can be connected with grounding device for transformer protective grounding.

The high voltage side of distribution transformer works in low resistance grounding system. When the grounding resistance of transformer protective grounding device meets the requirements of formula (5) and the building adopts total equipotential connection (including building reinforcement), the power supply grounding point of low-voltage system can be connected with transformer protective grounding device.

7.2.3 When the low-voltage system is powered by a single low-voltage power supply, the grounding resistance of the power supply grounding device shall not exceed 4Ω.

7.2.3 When the low-voltage system is powered by a single low-voltage power supply, the grounding resistance of the power supply grounding device shall not exceed 4Ω.

1- protection line; 2— Total equipotential bonding line; 3- ground wire; 4- auxiliary equipotential bonding wire;

B- total equipotential connection (grounding) terminal board; M-exposed conductive part; C- the conductive part outside the device; P- metal water main line; T-shaped grounding electrode

7.2.4 In the system, when the grounding point of the system and the exposed conductive part of the electrical device have been connected by total equipotential, there is no additional grounding device for the exposed conductive part of the electrical device. Otherwise, the exposed conductive part of the electrical device shall be provided with a protective grounding device, and its grounding resistance shall meet the requirements of the following formula.

R≤50/Ia？ ( 13)

? Ia-action current to ensure that the protection device cuts off the fault circuit, a.

7.2.5 The grounding device of the exposed conductive part of each electrical device in the system can be grounded with the same grounding device, or individually or in groups. The grounding resistance of each grounding device shall meet the following requirements

R≤50/Id ( 14)

? Id—— fault current of the first short-circuit fault between the phase line and the exposed conductive part, a.

7.2.6 When the first-class electrical devices are protected by ground fault, the electrical devices in the building should be connected by total equipotential connection. The following conductive parts shall be reliably connected through the main equipotential connection line and connected to the main equipotential connection terminal board at the entrance of the building (Figure 6):

Metal pipes such as water pipes, gas pipes, heating pipes and air conditioning pipes in buildings;

7.2.7 The iron foot of the insulator of household connecting wire should be grounded, and the grounding resistance should not exceed 30Ω. There is no need to set artificial grounding device for iron cross-arm reinforced concrete pole lines with soil resistivity of 200 Ω m or less. When the iron foot of the insulator is connected with the grounding device of the electrical device in the building, there is no need to set up another grounding device. When the natural grounding resistance of reinforced concrete poles is greater than 30 Ω, the iron feet of insulators should be grounded and special grounding devices should be set up.

In areas where the annual average thunderstorm days do not exceed 30 days, low-voltage lines are shielded by buildings. Or the grounding wire is not more than 50m away from the grounding point of the low-voltage line.

7.2.8 The grounding point of the low-voltage system power supply at the building, the protective grounding of the exposed conductive part of the electrical device (including the protective grounding of the functional grounding) and the grounding electrode of the total equipotential connection can use the same grounding device as the lightning protection grounding of the building. The grounding resistance of grounding device shall meet the minimum requirements.

The invalid grounding system should be a high resistance grounding system, and the resistance value is probably above 1000 ohm. Our common TN and TT systems are all effective grounding systems, and the grounding resistance is generally between 1 ~ 10. There are detailed provisions in the Code for Design of Grounding System of Ministry of Electric Power, and the number begins with DL.

The grounding resistance value of the signal ground of electronic equipment is not specified in IEC standards and national standards that adopt IEC standards equally or equivalently, as long as high-frequency low-impedance grounding (not necessarily grounding) and equipotential bonding are realized. When the common grounding is connected with other grounding systems, it shall be determined according to the minimum grounding resistance of other grounding systems.