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Earthing is the process of transferring the immediate discharge of electricity directly to the earth plate by using low-resistance electrical cables or wires.
The grounding wire safely removes excess electricity during a short circuit and passes it onto the ground, where it lies dormant. It is required for lighting protection, computer installations, hospital operation theaters, etc., for functional reasons.
- 1. Materials Specification
- 2. Location for Earth Electrodes
- 3. Installation of Earthing System
1. Materials Specification
1.1 Earth Electrodes
1.1.1 Types of Earth Electrodes
The different types of earth electrodes are as follows:
- Pipe earth electrode
- Plate earth electrode
- Strip or conductor earth electrode
1.1.2 Electrode Materials and Dimensions
- The materials and minimum sizes of earth electrodes shall be as per Table-1
- GI pipe electrodes shall be cut tapered at the bottom and provided with holes of 12 mm dia, drilled not less than 7.5 cm from each other up to 2 m of length from the bottom.
- The length of the conductor earth electrode or buried strip must be not less than 15m. This length can suitably be increased, if necessary, based on the data available on the soil resistance to obtain the required earth resistance.
|Type of Electrodes||Material||Dimension|
|Pipe||GI Medium class||40 mm dia, 4.5 mm long(without any joint)|
|Plate||1. GI||60 cm x 60 cm x 6 cm thick|
|2. Copper||60 cm x 60 cm x 3 mm thick|
|Strip||1. GI||100 sq.mm. section|
|2. Copper||40 sq. mm. section|
|Conductor||1. GI||5 mm dia (6 SWG)|
|2. Copper||4 mm dia (8 SWG)|
1.2 Earthing Conductor
The earthing conductor is a protective conductor from the earth electrode to the main earthing terminal/earth bus. The material specification of earthing conductor is:
- The earthing conductor shall be of the same material as the electrode (GI or copper) and in the form of wires or strips.
- The size of earthing conductor shall be specified, but this shall not be less than the following:
- 5 mm dia (6 SWG) for GI, or 4 mm dia (8 SWG) for copper wire,
- 25 mm x 4 mm in the case of GI strip
- 20 mm x 3 mm in the case of copper strip
- Earthing conductors larger than the following sectional areas need not be used unless otherwise specified.
- 150 sq. mm. In case of GI
- 100 sq. mm. In case of copper
1.3 Earth Bus
- Two copper strips, each of size 50 mm x 5 mm, shall be provided as earth bus in an 11 kV substation and diesel generating station irrespective of the capacity of the transformer or the DG Set.
- Each of these strips shall be connected to an independent earth electrode. The two earth leads from the body of each transformer/panel/generating set, etc., shall be connected to these two strips of earth bus.
- The neutral earth leads of the transformer and generator alternator shall not be connected to this earth bus. They shall be connected directly to individual earth electrodes.
1.4 Hardware Items
All hardware items used for connecting the electrode with the earthing conductor shall be GI in GI plate earth electrodes and forged tinned brass in case of copper plate electrodes.
1.5 Protective Conductor
- The minimum cross-sectional area of the protective conductor shall be:
- 2 mm dia (14 SWG) in case of copper
- 2.5 mm dia (12 SWG) in case of GI
- 2.24 mm dia (13 SWG) in case of aluminum.
- Unless otherwise specified, the GI conductor should not be ordinarily used as a protective conductor within any circuit beyond a DB downstream.
2. Location for Earth Electrodes
- Normally, an earth electrode shall not be located closer than 1.5 m from any building.
- Care shall be taken to see that the excavation for earth electrodes may be located further away from the building.
- The location of the earth electrode shall be such that the soil remains moist throughout the year.
- Entrances, pavements, and roadways should be avoided for locating earth electrodes.
3. Installation of Earthing System
3.1.1 Installation of Various types of electrodes
- The pipe electrode shall be buried in the ground vertically with its top at not less than 20 cm below the ground level.
- In locations where it is impossible to install the entire length of pipe electrode due to water table, hard soil, or rock, the length of the electrode may be reduced without compromising the required earth resistance.
- Plate electrode shall be buried in the ground with its face vertical, and its top, not less than 3 m below the ground level.
- When more than one electrode (pipe/plate) is installed, 2 m separation shall be maintained between two adjacent electrodes.
- The strip or conductor electrode shall be buried in a trench not less than 0.5 m deep.
3.2 Installation of Watering Arrangement
- In the case of plate earth electrodes, a watering pipe of 20mm dia. medium class pipe must be provided and attached to the electrodes.
- In pipe electrodes, a 40mm x 20mm reducer shall be used for fixing the funnel with mesh.
- The watering funnel attachment shall be housed in a masonry enclosure of size not less than 30 cm x 30 cm x 30 cm.
- A cast iron/MS frame with MS cover, 6 mm thick, and having locking arrangement shall be suitably embedded in the masonry enclosure.
3.3 Installation of Earthing Conductor
- In the case of a plate earth electrode, the earthing of the conductor shall be securely terminated onto the plate with two bolts, nuts, check nuts, and washers.
- In the pipe earth electrode, wire type earthing conductor shall be secured using nuts, washers, bolts, and washers and terminating socket.
- A double C-clamp arrangement shall be provided for earthing conductor with GI watering pipe for terminating tape type.
- The earthing conductor from the electrode up to the building shall be protected from mechanical injury by a medium class, 15 mm dia. in the case of wire, GI pipe, and 40 mm dia, medium class GI pipes in the case of the strip.
- The protection pipe in the ground shall be buried at least 30 cm deep.
- The earthing conductor shall be securely connected at the other end to the earth stud/earth bar provided on the switchboard by:
- Nut, bolt, and washer in case of strip conductor.
3.4 Earth Bus and Main Earthing Terminal
- In substations and generating stations, two copper/GI earth bus shall be provided, duly connected to two numbers of independent electrodes, exclusively for equipment (body) earthing of substation or generating station equipment.
- In all other installations, the main earthing terminal shall be provided at the main switchboard. This can be in the form of an earth stud or single earth bar, depending on the type of switchboard.
- Following conductors shall be terminated on to the main earthing terminal:
- Earth connection from an electric supply company.
- Earthing conductor from the electrode.
- Protective conductors.
- Equipotential bonding conductors.
3.5 Protective Conductor
- The earth terminal of every switchboard in the distribution system shall be bonded to the earth bar/terminal of the upstream switchboard by the protective conductor.
- Two protective conductors shall be provided for a switchboard carrying a three-phase switchgear thereon.
- All the mountings of industrial-type switchboards shall be bonded to the earth stud/earth bar using a protective conductor looping from one to another.
- The earth connector in every distribution board (DB) shall be securely connected to the earth stud or earth bar of the corresponding switchboard by a protective conductor.
- All metallic switch boxes and regulator boxes in a circuit shall be connected to the earth connector in the DB by the protective conductor, looping from one box to another up to the DB.
- The earth pin of socket outlets, the metallic body of fan regulators shall be connected to the earth stud in switch boxes by the protective conductor.
- In rising mains, bus trunking, etc., double earthing strips shall be securely connected to the earth bar/earth stud at the sending end switchboard.
- In the case of overhead busbar systems, protective conductors shall be provided in addition to feeder cable armoring connection.
3.6 Earth Resistance
- The earth resistance at each electrode shall be measured. No earth electrode shall have greater ohmic resistance than 5 ohms. In rocky soil, the resistance is allowed up to 8 ohms.
- Where the above-stated earth resistance is not achieved, necessary improvement shall be made by additional provisions, such as additional electrode(s), different types of electrodes, or artificial chemical treatment of soil, etc.
Earthing is transferring the immediate discharge of electricity directly to the earth plate by using low resistance electrical cables or wires.
The types of earth electrodes are as follows:
1. earth electrode
2. Plate earth electrode
3. Strip or conductor earth electrode
The size of earthing conductor shall be specified, but this shall not be less than the following:
1. 5 mm dia (6 SWG) for GI, or 4 mm dia (8 SWG) for copper wire
2. 25 mm x 4 mm in the case of GI strip
3. 20 mm x 3 mm in the case of copper strip
The minimum cross-sectional area of the protective conductor shall be:
1. 2 mm dia (14 SWG) in case of copper
2. 2.5 mm dia (12 SWG) in case of GI
3. 2.24 mm dia (13 SWG) in the case of aluminum.