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TN-S - Additional PE Conductor

Nick Parker

Why in TN-S System PE Cables have to be provided in addition to the phase conductors for each loads (like socket, light fixture, Motor etc.)?
Don't bonding the enclosure of the loads (socket, fixtures, Motors etc.) to the local earth electrode or grid makes it sufficient and the fault current takes the route of enclosure --> earth electrode / grid --> return via mother earth to the source?

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    If the earth path is metallic, and only carries fault currents be it through cables or conduits or trunking, it is TNS 

    You can use  the conduit or whatever as the earth path but you must arrange it so accidental disconnection of the earth  is very unlikely, and it can carry the full prospective current, if you cannot be sure of that, then a copper earth path is in order, either all the way or just to bypass the bits where we are less sure of reliable connection. Painted metal  and clip on lids  are our enemies here, and anything that may vibrate loose.

    If the earth path also carries load currents as well as just faults, then it is TNC.

    If the fault current path involves terra-firma, then it is TT.

    Many systems are a mix of TNC and TNS - it sort of depends how the distribution is done.

    Mike

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  • 0

    If the earth path is metallic, and only carries fault currents be it through cables or conduits or trunking, it is TNS 

    You can use  the conduit or whatever as the earth path but you must arrange it so accidental disconnection of the earth  is very unlikely, and it can carry the full prospective current, if you cannot be sure of that, then a copper earth path is in order, either all the way or just to bypass the bits where we are less sure of reliable connection. Painted metal  and clip on lids  are our enemies here, and anything that may vibrate loose.

    If the earth path also carries load currents as well as just faults, then it is TNC.

    If the fault current path involves terra-firma, then it is TT.

    Many systems are a mix of TNC and TNS - it sort of depends how the distribution is done.

    Mike

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