Earthing / Grounding work has to comply with the requirements of General and Technical Conditions of the Project including statutory obligations and regulations. Submittals to be approved by project consultant prior execution of the actual work. Regulations and rules of supply authority also to be considered when preparing the submittals for the local in which installation is being constructed.
Lightning Protection System should be in accordance with BS 6651 and IEC 61024 to protect the building structure and personnel from the risk of a lightning strike. The installation shall comprise air networks connected to roof and down conductors and finally terminated in earth electrodes, via structural re-bars and suitable test points in accordance with the details included on the attached drawings or in the Specification Section.
The Contractor shall carry out an earth resistivity survey on each site and report in writing to the Engineer in accordance with the approved program. The report shall detail the methods and instruments used and the results of the surveys. Based on the results the Contractor shall include in the report his proposals for the resistivities to be used in the design of the earthing system.
Electrical Earthing or Grounding System for buildings to be carried out all in accordance with the international standards in conjunction with the local authority requirements and recommendations. Earthing standards and methods are highly depending on the nature of the utilities and equipment installed / used at the premises. Simple earthing system we provide to the domestic connections while complex systems are being used in the power stations and industries.
Earth electrode resistance, Insulation resistance of factory-built materials installed at the site and Insulation resistance of site-built materials installed at site to be considered individually for filed quality control check. It is further to be monitored earth resistance of individual earth unit and combined resistance of earth units.
Continuity to be ensured that complete earthing system is electrically continuous and mechanically secure. Locations of main earth bars in substations, electrical rooms, mechanical rooms, hub (Technical) rooms, etc., to be clearly identified by 100mm X 100mm white traffolyte labels, with red lettering, to Engineer's approval.
Earthing or Grounding Electrode for an effective and reliable electrical earthing system requires proper survey and analysis of project location, type of structures installed and electrical / electronic equipments used in the entire system. The design calculation of the earth electrode systems shall be based on the approved earth resistivity data and the system's fault currents and their duration.
Signal and Communication Systems: For telephone, alarm, voice and data, and other communication systems, provide 16 mm2 minimum insulated grounding conductor in raceway from a separate grounding electrode clean system to each service location, terminal cabinet, wiring closet, and central equipment location.
A. Ground Rod:
16 mm diameter stainless steel. Driving head is to be high strength steel. Couplings are to be long length silicon bronze, internally threaded. Threads are to be rolled onto rod to ensure uniform layers of copper and strength. Earth rod is to be complete with non-corrosive couplings, head and bolted connector of sufficient size, and number of bolted clamps to connect all cables terminated thereto.
Buried Earth Conductors: PVC insulated copper strip conductors or PVC insulated stranded copper cables with cross-section min 70 mm2 or as per earthing calculation.
Earthing Conductors: PVC insulated copper conductor as described in the Specification for the particular application.
In the electrical point of view and as a safety measure, metallic fence shall be separately earthed unless they come within 1.8 m of any equipment or structure above the surface of the ground, which is connected to the main earthing system. If the separation of 1.8 m cannot be obtained the fence shall be bonded to the earthing system. Here is how compound fences connecting to the earthing system.
MV switchgear and MV cables are to have separate main earthing bar connected to framework or earth bar of each item by insulated conductor and the earth-electrode by 2 insulated earthing conductors, one at each end of bar, via testing joints. Earthing conductor is to be minimum 150 mm2.
Earthing Cables: Separate protective earthing cables for lighting column circuits are to be run with power circuit, terminated at LV supply position in lighting control panel and looped into column earthing terminals. The last column is to be bonded via an earthing bolt to a single 16 mm diameter stainless steel rod, 3.6 m long, driven into ground adjacent to column. Bonding is to be 16 mm2 stranded bare copper conductor.
A. Main earthing bar or loop is to be conveniently located in electrical/mechanical plant rooms, and connected by earthing conductors to exposed conductive parts of motor control centre at its earthing bar, and to motors, switches and other electrical equipment etc. at their earthing terminals, using 20 x 2 mm insulated copper strips or 35 mm2 insulated copper conductor (minimum size) or as required to carry maximum earth fault current for 1 second with final conductor temperature not exceeding 200 deg. C (392 deg. F).
Generator neutral (star point) is to be connected by insulated earthing conductor through the neutral earthing link or device to main earthing bar. Neutral earthing conductor is to be suitably sized to carry maximum earth fault current for time it takes the system protection to operate with final conductor temperature not exceeding 160 deg. C, but not less than 30 mm2 per 100 kVA of generator rating, with a minimum of 50 mm2.
The metallic sheath and armour of multicore cables shall be bonded together and earthed. Cable earthing conductors shall be copper strip with appropriate section laid in formed cable trenches or ducts, or fixed to walls, concrete or steel work, by means of clamps or claw type cleats, appropriately secured into suitable wall plugs or tapped holes. The spacing of fixings shall not be greater than 1 m.
A. Protection against Corrosion: Protect bolted connections against corrosion either hy filling with vaseline or coating with a special anti-corrosion compound and proper capping (Denso tape / grease caps).
B. Connections: Earth connections are to be readily accessible. If inaccessible earth connection is permitted, approved exothermic welding or brazing technique is to be employed.
Clean earth grounding or low noise earth shall be provided as required, to ensure that the level of induced or conducted interference from external sources, including the facility power grounding system, does not produce incidence of malfunction of the equipment, which is unacceptable for the operating system.
In electrical projects, both construction as well as maintenance, the following terms used on the Drawings, Specifications and in the actual Work site are equivalent and may be used interchangeably: "earth" and "ground"; "earthing" and "grounding". Besides, this article tries to rectify mis-interpretation of some important terms often used by people involved in the electrical earthing / grounding work.
Connector Products And Accessories for Electrical Earthing or Grounding System shall be as follows:
Copper or copper alloy, purpose made, of approved design, compatible with points of connection, and of adequate cross-section and current carrying capacity. Connections to metallic structures for earthing conductors and bonding conductors between electrically separate parts of a structure shall be either by direct exothermic welding or by bolting using a stud welded to the structure.