Earthing system

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It is perfect for Internet Marketers, Small Business, Social Organizations, Individuals and Beginners. You may find Contents1 In household wiring 2 IEC terminology 2.1 TN network 2.2 TT network 2.3 IT network 3 Other terminologies 4 Properties 4.1 Cost 4.2 Safety 4.3 Electromagnetic compatibility 5 Regulations 6 Application examples 7 See also 8 References // In electricity supply systems, an earthing system defines the electrical potential of the conductors relative to that of the Earth's conductive surface. The choice of earthing system has implications for the safety and electromagnetic compatibility of the power supply. Note that regulations for earthing (grounding) systems vary considerably between different countries.A protective earth (PE) connection ensures that all exposed conductive surfaces are at the same electrical potential as the surface of the Earth, to avoid the risk of electrical shock if a person touches a device in which an insulation fault has occurred. It ensures that in the case of an insulation fault (a "short circuit"), a very high current flows, which will trigger an overcurrent protection device (fuse, circuit breaker) that disconnects the power supply.A functional earth connection serves a purpose other than providing protection against electrical shock. In contrast to a protective earth connection, a functional earth connection may carry a current during the normal operation of a device. Functional earth connections may be required by devices such as surge suppression and electromagnetic interference filters, some types of antennas and various measurement instruments. Generally the protective earth is also used as a functional earth, though this requires care in some situations.In household wiringThere are two main approaches to the problem of how to disconnect power when a live wire comes into contact with metalwork attached to the earthing system: One way is to get the resistance through the fault path and back to the supply very low by having a metallic connection from the earth back to the supply transformer (a TN system). Then when a fault happens a very high current will flow rapidly blowing a fuse (or tripping a circuit breaker).The second approach, where such a direct connection is not used (a TT system), the resistance of the fault path back to the supply is too high for the branch circuit overcurrent protection to operate (blow a fuse or trip a circuit breaker). In such case a residual current detector is installed to detect the current leaking to ground and interrupt the circuit.IEC terminologyInternational standard IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT.The first letter indicates the connection between earth and the power-supply equipment (generator or transformer):T:direct connection of a point with earth (Latin: terra);I:no point is connected with earth (isolation), except perhaps via a high impedance.The second letter indicates the connection between earth and the electrical device being supplied:T:direct connection with earth, independent of any other earth connection in the supply system;N:connection to earth via the supply network.TN networkIn a TN earthing system, one of the points in the generator or transformer is connected with earth, usually the star point in a three-phase system. The body of the electrical device is connected with earth via this earth connection at the transformer.The conductor that connects the exposed metallic parts of the consumer is called protective earth (PE). The conductor that connects to the star point in a three-phase system, or that carries the return current in a single-phase system, is called neutral (N). Three variants of TN systems are distinguished:TN?S:PE and N are separate conductors that are connected together only near the power source.TN?C:A combined PEN conductor fulfills the functions of both a PE and an N conductor.TN?C?S:Part of the system uses a combined PEN conductor, which is at some point split up into separate PE and N lines. The combined PEN conductor typically occurs between the substation and the entry point into the building, whereas within the building separate PE and N conductors are used. In the UK, this system is also known as protective multiple earthing (PME), because of the practice of connecting the combined neutral-and-earth conductor to real earth at many locations, to reduce the risk of broken neutrals - with a similar system in Australia being designated as multiple earthed neutral (MEN).TN-S: separate protective earth (PE) and neutral (N) conductors from transformer to consuming device, which are not connected together at any point after the building distribution point....(and so on) To get More information , you can visit some products about student discount computer, cormet testing system, . The Internet Marketing products should be show more here!