19 grounding electrode installation standards

19 grounding electrode installation standards:

1. The grounding device should be made of steel, and the conductor cross-section of the grounding device should meet the requirements of thermal stability and mechanical strength.

2. The top surface of the grounding body should be buried at a depth of no less than 0.6 meters, and the angle steel and steel pipe grounding bodies should be arranged vertically. In addition to the grounding body, the lead-out wire of the grounding body should be treated with anti-corrosion; when galvanized flat steel is used, the bolt connection part of the lead-out wire should be painted with anti-corrosion paint.

3. In order to reduce the shielding effect of adjacent grounding electrodes, the spacing between vertical grounding electrodes should not be less than twice their length, and the spacing between horizontal grounding electrodes should be based on design requirements and should not be less than 5 meters.

4. The distance between the grounding body and the building should not be less than 1.5m.

5. The grounding wire should be protected from mechanical damage and chemical corrosion. When passing through the wall, the grounding wire should pass through an open hole and be placed in a steel pipe or other sturdy protective cover.

6. The grounding main line should be connected to the grounding grid at least at two different points.

7. Each grounded part of the electrical installation should be connected to the grounding trunk line with a separate grounding wire, and several parts that need to be grounded shall not be connected in series in one grounding wire.

8. After the grounding electrode is laid, the backfill soil in the trench should not contain stones, construction materials or garbage.

9. The installation of exposed grounding wires shall comply with the following requirements:

(1) To facilitate inspection;

(2) The installation location should not hinder the disassembly and maintenance of the equipment;

(III) The distance between supports is generally 1-1.5 meters in horizontal straight sections, 1.5-2 meters in vertical sections, and 0.5 meters in turning sections.

(iv) The grounding wire should be laid horizontally or vertically, but it can also be laid parallel to the inclined structure of the building. There should be no ups and downs or bends on the straight section.

(V) When the grounding wire crosses the expansion joint or settlement joint of a building, a compensator should be installed. The compensator can be replaced by the grounding wire itself bent into an arc shape.

10. The surface of the exposed grounding wire should be painted black. If it is necessary to paint other colors due to the design requirements of the building, two black stripes with a width of 15 mm each should be painted at the connection and branch points, with a spacing of 150 mm. The exposed grounding wire with the neutral point connected to the grounding grid should be painted purple with black stripes.

11. At the entrance where the grounding wire leads into the building, it should generally be marked with a black mark "". At the temporary grounding point for maintenance, it should be painted with white primer and then marked with a black mark "".

12. When carrying out maintenance work, temporary grounding is required in places such as distribution bays, busbar sections,

The lead-out wire room, etc. should be connected to the grounding main line, and a grounding plate and

bolt.

13. The grounding wire should be connected by welding, and the welding must be firm and without voids. The grounding wire connected to the electrical equipment should be connected by bolts; when non-ferrous metal grounding wires cannot be welded, they can be connected by bolts. The contact surface of the bolt connection should be surface treated as required.

14. The connection of the grounding wire (body) should be lap welded, and the welding length must be:

(a) Twice the width of the flat steel (and at least three edges are welded);

(ii) 6 times the diameter of the round steel;

(III) When welding flat and round steel (or angle steel), in order to ensure reliable connection, in addition to welding on both sides of the contact part, arc-shaped (or right-angled) clips bent from steel strips should be welded, or the steel strips themselves should be directly bent into an arc (or right-angled) shape and welded to the steel pipe (or angle steel).

15. During acceptance, the following inspections shall be carried out:

(1) The exposed part of the entire grounding grid is reliably connected, the grounding wire specifications are correct, the paint is intact, and the markings are complete and clear.

(2) The number and position of connection plates used for connecting temporary grounding wires meet the design requirements.

16. During acceptance, the following information and documents shall be submitted:

(1) the actual construction drawings of the changed design parts;

(2) Documents proving the design change;

(3) Installation technical records (including hidden engineering inspection records, etc.);

(iv) Test records (ground resistance test records).

1. Measurement of ground resistance

The grounding resistance of the grounding device is related to the effectiveness of the protective grounding (zero) and the operation of the power system. The actual value of the grounding resistance must be measured before and during the use of the grounding device to determine whether it meets the requirements.

At present, the commonly used methods for measuring ground resistance are mainly the current-voltmeter method and the ground resistance measuring instrument method.

2. For low-voltage electrical equipment with direct or indirect neutral grounding: (1) When the total capacity of the electrical equipment in parallel operation is more than 100KVA, the grounding resistance shall not be greater than 4 ohms; (2) When the total capacity of the electrical equipment in parallel operation does not exceed 100KVA, the grounding resistance shall not be greater than 10 ohms;

17. Measures to reduce grounding resistance:

In soils with high resistivity (such as rock, sand and long-term frozen soil), it is difficult to meet the specified grounding resistance. To reduce the grounding resistance, the following measures can be taken:

1. Use clay, black soil and sandy soil with lower resistivity to replace the original soil with higher resistivity. Generally, replace the soil within 0.5 meters around the upper 1/3 length of the grounding body.

2. For sandy soil, the burial depth of the grounding body can be increased. Deep burial can also ignore the influence of increased resistivity caused by soil freezing and drying.

3. Artificial treatment of soil, generally by adding salt to the soil. According to experimental results, after the soil is treated with salt, the resistance of sandy clay is reduced by 1/3~1/2, the resistance of sand is reduced by 3/5~3/4, and the resistance of sand can be reduced by 7/9~7/8. For rocky soil, after being impregnated with 1 salt solution, its conductivity can be increased by 70, and the conductivity of granite can be increased by 1200 times. However, after the soil is artificially treated, the thermal stability of the grounding body will be reduced, the corrosion of the grounding body will be accelerated, and the service life of the grounding body will be reduced. Therefore, when the grounding resistance can be achieved by natural methods, artificial treatment methods are generally not used.

4. If the frozen soil still cannot meet the requirements after artificial treatment, it is best to bury the grounding body under the building, or use peat filling method in winter.

18. Application scope of grounding and zero connection

Protective grounding is applicable to neutral point grounding power grids. Three-phase four-wire neutral point grounding power grids should adopt protective grounding measures. All metal parts that may present dangerous voltages due to insulation damage or other reasons should be grounded or zeroed.

1. Equipment that should be grounded or zeroed

1) Metal casings, bases and transmission devices connected to motors, transformers, electrical appliances, lighting fixtures, portable and mobile electrical appliances, etc.

2) Metal frames or reinforced concrete frames of indoor and outdoor power distribution equipment and metal guardrails, fences or metal doors close to live parts.

3) Metal frame or casing of distribution panel, control desk, console and control box.

4) Secondary winding of transformer.

5) Metal casing of AC and DC power cable junction boxes, metal sheath of cables and steel pipes for wiring, etc.

6) Metal poles and reinforced concrete towers of power lines equipped with lightning arresters.

7) Electrical equipment such as switches and capacitors installed on distribution line poles.

2. Equipment that does not require grounding or zeroing

1) In a dry room with non-conductive floors such as wood and asphalt, the casing of electrical equipment with AC 380V and below and DC 400V and below (when maintenance and repair may touch the casing of the electrical equipment and other grounded devices at the same time, it should still be grounded).

2) In dry general places, the enclosure of electrical equipment with an AC rated voltage of 127V or less and a DC rated voltage of 110V or less (except in explosive places).

The outer casings of electrical measuring instruments, relays and other low-voltage electrical appliances installed on distribution panels, control boxes and distribution devices, as well as the metal bases of insulators that will not cause dangerous voltages on the supports when insulation damage occurs.

3) Equipment installed on a grounded metal frame and in good contact with the frame, such as bushings (except in explosion-hazardous areas).

4) Electrical equipment installed at height. Workers must climb a wooden ladder to approach and work, because the risk of accidental human contact with live parts is small, but the possibility of human contact with live parts and the equipment casing at the same time is high.

19. Comparison between grounding and zero connection

1. The similarities between protective grounding and protective zero connection

1) In low-voltage systems, technical measures are taken to prevent electric shock accidents caused by leakage.

2) The locations where grounding and neutral connection are required to be roughly the same.

3) Both grounding and neutral connection require certain grounding devices, such as protective grounding devices, working grounding devices and repeated grounding devices. Moreover, the construction and connection of the grounding bodies and grounding wires of each grounding device are basically the same.

2. Differences between protective grounding and protective zero connection

1) Different protection principles

The basic principle of low-voltage system protective grounding is to limit the voltage of leakage equipment to the ground so that it does not exceed a certain safety range. Protective grounding is to use the grounding line to form a single-phase short circuit when the equipment leaks, prompting the protection device on the line to act quickly. Secondly, the protective neutral line and repeated grounding in the protective grounding system also have a certain voltage reduction effect.

2) Different scope of application

Protective grounding is applicable to general low-voltage power grids with ungrounded neutral points, and protective zeroing is applicable to low-voltage power grids with directly grounded neutral points.

3) Different line structures

The protective grounding system only has a protective ground wire. The protective zeroing system must have a working neutral wire, working grounding and repeated grounding. If necessary, the protective neutral wire and the working neutral wire must be separated.