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What earthing arrangement is this?

Former Community Member
Former Community Member
The supply is from a private transformer in a four core cable 3ph + n. The cable armour is earthed and connected to the MET. However there is also a green and yellow cable connected to the neutral terminal at the main isolator going back to a the transformer casing. The transformer is only 5 or 6 metres away. I think this must have been intended to make it a tncs supply but seems to me to just create parallel neutral conductors. Or is it tn-s-c-s?  I have only been able to go off visual inspection because I could not disconnect the supply..
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  • 0

     "The transformer tank and associated HV metalwork shall be connected to the HV earth electrode." If there is a combined HV/LV earth electrode, that might explain things, but is it allowed?





    Yes it is, but the Rise of Earth Potential must be calculated first to make sure the site is “cold” less than 430V or less than 650V with fast protection. 


    Regards,


    Alan.
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  • 0

     "The transformer tank and associated HV metalwork shall be connected to the HV earth electrode." If there is a combined HV/LV earth electrode, that might explain things, but is it allowed?





    Yes it is, but the Rise of Earth Potential must be calculated first to make sure the site is “cold” less than 430V or less than 650V with fast protection. 


    Regards,


    Alan.
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