Published:
5 November 2004
Category:
Q&A
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Answer:
In a TN-S system both the neutral and protective conductors are separate within the supply and within the installation. Normally the means of earthing is provided from the supply cable metallic sheath or other separate supply conductor.
In a TN-C-S system the neutral and earth are combined within the supply and separate within the installation. The means of earthing is provided from the combined protective and neutral conductors of the supply i.e. a PME earthing terminal.
In a TT system there is no earth terminal provided from the supply and an earth is provided by separate earth electrodes, normally supplemented by one or more Residual Current Devices (RCDs).