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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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    I'm looking at the question differently.

    If we distribute the Neutral as a live conductor (as we do now in a TN-S or TN-C_S system), could we not provide PE via direct bonding to an “earth reference plane” which is connected to the PE distributed to each switchboard and distribution board?

    The answer to the question phrased in that way is, that it could be done, but there's the potential issue of earth fault currents causing movement of the live conductors if the cpc is not “in the same wiring system or its immediate proximity”. (Regulation 543.5.1).

    Having said that, I would have thought in many locations where an earth reference grid or plane is in use (e.g. data centre and similar installations with earthing to BS EN 50310), most of the earth fault current flows back through the common bonding network (CBN) rather than the cpc, which I guess somewhat deflates the importance of Regulation 543.5.1 in this type of installation? 

    The only issue to address for 543.5.1 in terms of , is to ensure that metallic armour, or containment containing insulated (but not sheathed) cables is suitable for use as a CPC for the largest fault current  of a circuit contained within it, or is suitable backed up by a parallel cpc.
     

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  • 0

    I'm looking at the question differently.

    If we distribute the Neutral as a live conductor (as we do now in a TN-S or TN-C_S system), could we not provide PE via direct bonding to an “earth reference plane” which is connected to the PE distributed to each switchboard and distribution board?

    The answer to the question phrased in that way is, that it could be done, but there's the potential issue of earth fault currents causing movement of the live conductors if the cpc is not “in the same wiring system or its immediate proximity”. (Regulation 543.5.1).

    Having said that, I would have thought in many locations where an earth reference grid or plane is in use (e.g. data centre and similar installations with earthing to BS EN 50310), most of the earth fault current flows back through the common bonding network (CBN) rather than the cpc, which I guess somewhat deflates the importance of Regulation 543.5.1 in this type of installation? 

    The only issue to address for 543.5.1 in terms of , is to ensure that metallic armour, or containment containing insulated (but not sheathed) cables is suitable for use as a CPC for the largest fault current  of a circuit contained within it, or is suitable backed up by a parallel cpc.
     

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