Earthing Systems

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Traineeboy

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I understand the difference between the 3 main earthing system but I saw an earthing system in a house that looked like a combi of a TN-S and a TN-C-S system. I.e there was a main earthing conductor coming out the sheath of the cable but also a main earthing conductor coming of the service head. Anyone know that this could be ? 

 
see it often... probably was TNS, the TNS earth has failed so instead of doing the job properly and diggin up the road to fix the problem, DNO take the lazy option and make it TNCS....

 
Ok thanks. Would you then make sure that both main earthing conductors would be connected or would you isolate the TN-S or would just use the one with the best reading ? 
 

 
if its linked N-E then it cannot be TNS anymore and is TNCS

also be aware of disconnecting them from each other - that link is also an earth path for the DNO's cable and potentially other properties depending where the TNS earth fault is...

 
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