Q & A of the Day – A TT system with earth spike or a TNC-s?

Question: I am currently undertaking a re-wire to a property built circa 1960s. I believe that the supply to be a TN-s system as the original earth was taken from the metal casing where the incoming cable was terminated and was 4mm CSA! There is no clamp on the armour of the incoming cable.

When I performed a Ze on the original earth, I recorded readings of 800 ohms plus. Will I have to change the system to a TT and install an earth spike, or is it acceptable to change the system to a TNC-s by connecting into the neutral block. Alternatively, is it the responsibility of the distributor to supply the earth connection?

Answer: The distributor is not obliged to provide an earth for an existing installation. If no earth is present, the distributor should be consulted regarding the provision of an earthing facility but, if willing to do so, it may charge for such provision.

If the distributor is not willing to provide an earth, or the client will not pay for its provision, the only option is to provide a TT earthing system. Use of the supply neutral connection as the means of earthing is not an option.

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