Technical Information Power And Control Cables Power Appendixes Guide to the Wiring Regulations Residual current and Surge protection of system صفحه Residual current and Surge protection of system
| Residual current and Surge protection of system | |
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When an earth fault or earth leakage is present on a circuit, a small ‘imbalance’ is set up in the detection coil and, at a certain level, causes a trip of the circuit breaker mechanism . Residual current devices monitor the instantaneous current fowing along the line and neutral conductors in a circuit by means of a sensitive coil. The coil or ‘core’ measures the instantaneous resulting sum of these currents. . A diagrammatic representation of this is shown in following Figure : |
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Surge protective devices (SPD) : Surge protective devices (SPDs) may optionally be specifed. If you are the designer you may feel that they add a certain security to an installation. SPD selection and installation comes down to a few simple rules, summarized as follows: * Choose SPDs complying with IEC 61643 series. * In TN-C-S installations connect device between line conductors and earth. * In TN-S and TT installations connect device between line conductors and both neutral and earth. |
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| Connection of SPD in TN-C-S system (PME). | |
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| Connection of SPD in TT system | |
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| Connection of SPD in TN-S system. |
Application examples of residual current monitors (RCM) : In a larger installation a three-phase RCM device positioned in the main distribution board will be extremely useful. These devices can be widely used and above Figure indicates examples of where RCMs are used in mains, riser and fnal distribution board positions. |
