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T-N-S or TN-C-S ???? Help pls.

MrFox

I have been asked to replace a consumer unit. All seems fine, and the incoming earth seems to be on the sheath of the incomer, so, TN-S. But, it says TN-C-S on the previous EICR. Did that spark make a mistake or is there something here I'm missing? Also, do we presume the Line and Neutral are in that cable going to the meter??? I hope so… Thx in advance.

b13f6e8ca4a8740403be79c8a45433ce-huge-tns_or_tncs.png
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    greater than 230/Ze, TN-S is more likely.

    Or it can also be less. Some pre-war lead cable has a lot of lead, and is a bit thin on the copper by modern standards. - was a lights only supply got upgraded that sort of thing. ? 

    In the high Zs extreme, also the underground joints can fail or something chews the lead leaving about 3 feet of lead pipe underground acting as an accidental earth electrode and then a gap .  Only a proper Zs test with the plumbing bonds interrupted will actually find that, and it is worth checking for that on older cables - if you get a TT sort of Zs, say  tens of ohms, then just maybe that has happened - then it is call the DNO time.

    Mike

     

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  • 0

    greater than 230/Ze, TN-S is more likely.

    Or it can also be less. Some pre-war lead cable has a lot of lead, and is a bit thin on the copper by modern standards. - was a lights only supply got upgraded that sort of thing. ? 

    In the high Zs extreme, also the underground joints can fail or something chews the lead leaving about 3 feet of lead pipe underground acting as an accidental earth electrode and then a gap .  Only a proper Zs test with the plumbing bonds interrupted will actually find that, and it is worth checking for that on older cables - if you get a TT sort of Zs, say  tens of ohms, then just maybe that has happened - then it is call the DNO time.

    Mike

     

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