Purposes and Types of Earthing Systems
– Earthing systems serve the purpose of electrical safety and functionality.
– The choice of earthing system can impact safety and electromagnetic compatibility.
– Regulations for earthing systems vary among countries.
– Earthing systems are used in various applications, such as mines, patient care areas, and industrial plants.
– Other systems, like tall structures, telegraph lines, and radio antennas, may also require grounding for safety and operation.
– TN-S, TN-C, TN-C-S, TT, and IT are different types of earthing systems.
– TN networks (TN-S, TN-C, TN-C-S) allow for easy automatic disconnection in case of a line-to-PE short circuit.
– TT networks use local earth electrodes for consumer and generator connections.
– IT networks have no connection to earth or a very high-impedance connection.
– Resistance earthed neutral is used in mining in India to limit fault current.
– Different countries have variations in the introduction of earthed contacts in power outlets.
System Earthing
– System earthing ensures electrical safety throughout the system.
– It prevents static buildup and protects against power surges caused by lightning strikes or switching.
– Static buildup induced by friction is dissipated to the Earth.
– Lightning arresters or surge arresters divert excess current to the Earth during a surge.
– System earthing allows for equipotential bonding and limits potential differences between metalworks.
Equipment Earthing
– Equipment earthing ensures electrical safety in the event of an electrical fault.
– It prevents equipment damage and the risk of electric shock.
– When current flows from a line conductor to an earth wire, an automatic disconnection of supply device opens the circuit to clear the fault.
– Equipment earthing is crucial for the safety of Class I appliances.
– Equipment earthing is not technically an earth connection.
Functional Earthing
– Functional earthing serves purposes other than electrical safety.
– It includes electromagnetic interference (EMI) filtering in EMI filters.
– The Earth is used as a return path in single-wire earth return distribution systems.
– Functional earthing is essential for the proper operation of certain systems.
– It helps control static electricity and provides lightning protection.
Low-voltage Systems and Safety Considerations
– In low-voltage networks, the design of earthing systems prioritizes consumer safety.
– The earthing system, along with protective devices, ensures protection against electric shocks.
– The threshold for safe potential difference is typically set at around 50V.
– Different countries have variations in the introduction of earthed contacts in power outlets.
– Safety considerations for low-voltage systems are equally important in industrial and mining applications.
– RCDs (residual-current devices) are usually employed for safety in electrical installations.
– TN-S and TT systems use RCDs for additional protection.
– IT and TN-C networks are less likely to detect insulation faults.
– TN-C systems should wire RCDs to only interrupt the line conductor.
– TN-C-S supplies are banned in the UK for certain applications due to safety risks. Source: https://en.wikipedia.org/wiki/Earthing_system
An earthing system (UK and IEC) or grounding system (US) connects specific parts of an electric power system with the ground, typically the Earth's conductive surface, for safety and functional purposes. The choice of earthing system can affect the safety and electromagnetic compatibility of the installation. Regulations for earthing systems vary among countries, though most follow the recommendations of the International Electrotechnical Commission (IEC). Regulations may identify special cases for earthing in mines, in patient care areas, or in hazardous areas of industrial plants.
In addition to electric power systems, other systems may require grounding for safety or function. Tall structures may have lightning rods as part of a system to protect them from lightning strikes. Telegraph lines may use the Earth as one conductor of a circuit, saving the cost of installation of a return wire over a long circuit. Radio antennas may require particular grounding for operation, as well as to control static electricity and provide lightning protection.
