TN-C-S supply, shocks from earthed sink, latest test from landlord 200Mohm resistance between E/N

[UnderstandingElectrics]

TN-C-S supply, shocks/tingles from earthed sink.

Latest NICEIC test (2017) from landlord shows 200Mohm resistance between E and N

As above, do I have a floating neutral, is this causing a leak from N, via bonding on sink to true earth (solid kitchen floor)?

 

[brianmoooore]

TNC-S means that the earth and neutral wires of the installation are physically connected together at the supplier's cut out. Anything other than a resistance of very close to zero should have raised questions, and an unsatisfactory EICR issued.
Who said it's TNC-S? Initial thoughts are that there's no earth provided by the supplier.

 

[westward10]

A routine test is not likely to show a test between the suppliers neutral and earth. This is almost likely to be a breakdown of the earthing conductor connection, an electrician will be able to confirm this.

 

[UnderstandingElectrics]

TNC-S means that the earth and neutral wires of the installation are physically connected together at the supplier's cut out. Anything other than a resistance of very close to zero should have raised questions, and an unsatisfactory EICR issued.
Who said it's TNC-S? Initial thoughts are that there's no earth provided by the supplier.

Hi Brian,

Thanks for the speedy reply. TN-C-S is noted on both:

1. the 2017 Landlord's inspection report (where E/N is supposedly tested @ 200Mohm). I assume this covers the incoming main, cleaners supplies, common part lighting and
   
   
2. my EICR (2019) for my own flat, which also refers to the building's earthing arrangement. The electrician who did my report didn't have sight of the landlord's report. I haven't managed to get in contact with the electrician who did my EICR, but he was registered (NAPIT). As far as I can tell there's no record of the resistance measured between E/N on my EICR - it's like the testing results page is not in the document, apart from the results from the individual circuits (I didn't notice until now).

It seems to me as if there's a mismatch between the assumed? supply type and the insulation of E/N.

 

[UnderstandingElectrics]

A routine test is not likely to show a test between the suppliers neutral and earth. This is almost likely to be a breakdown of the earthing conductor connection, an electrician will be able to confirm this.

Thank you for taking the time to reply. Would I be right in assuming this likely to be close to wherre the service enters the building, rather than within my flat, or are either possible?

 

[westward10]

Thank you for taking the time to reply. Would I be right in assuming this likely to be close to wherre the service enters the building, rather than within my flat, or are either possible?

Difficult to say without being there but somewhere along the line the earth has almost certainly failed.

 

[UnderstandingElectrics]

Difficult to say without being there but somewhere along the line the earth has almost certainly failed.

Thank you again. If the installation earth has failed, does this mean current is flowing from neutral to true earth (via feet to kitchen floor), because the installation E/N and true earth are not at the same potential?

I'm trying to wrap my head around it, as the only potential source of current I can see is the bonding onto the sink, and the issue is diminished by wearing something insulating (rubber soled shoes) on the solid floor which would tell me current is going to true earth.

Not that I'm going to be able to fix it!

 

[LeeCage]

While probably not the problem here (if it really is TN-C-S) I had a similar problem some years ago in an old Victorian house (recently rewired). One day, after a few years with no problems, I started getting tingles off the washing machine. To cut a long story short, it turned out that the earthing in the house relied on the cold water supply. Recently, the water pipe had been replaced with a plastic one. Hey presto, no earthing anywhere! Of course, the plumber involved hadn't a clue.

 

[brianmoooore]

All it takes is for a plumber to replace one strategically placed metal fitting with a plastic one, or to insert one, for the above to apply.

 

[TJ Anderson]

Hi Brian,

Thanks for the speedy reply. TN-C-S is noted on both:

1. the 2017 Landlord's inspection report (where E/N is supposedly tested @ 200Mohm). I assume this covers the incoming main, cleaners supplies, common part lighting and
   
   
2. my EICR (2019) for my own flat, which also refers to the building's earthing arrangement. The electrician who did my report didn't have sight of the landlord's report. I haven't managed to get in contact with the electrician who did my EICR, but he was registered (NAPIT). As far as I can tell there's no record of the resistance measured between E/N on my EICR - it's like the testing results page is not in the document, apart from the results from the individual circuits (I didn't notice until now).

It seems to me as if there's a mismatch between the assumed? supply type and the insulation of E/N.

Where exactly was the 200Mohm value recorded on the schedule of tests?

As I read it, it sounds like he is actually refering to final/dist circ insulation resistance tests. These are dead tests which would have be carried out with the main switch isolated anyway and subsequently 200Mohm would be a value you would actually hope for (as this disconnects the N-E link from cut out).Might be giving him too much credit and it may just be a made up global >200 IR like on most EIC/EICR's you see these days lol.

What was the Ze recorded on cert?

What main protective bonding is in place?

Another one for you to find out and test for.....Is there any supplementary bonding on pipework to sink and what resistance is there between it and MET?

 

[James]

It has not been said in this thread yet as everyone is trying to answer the question about how you are getting a shock.

however, the advice that you should take note of is as follows.

Any electric shocks should be reported to your landlord as an immediate safety concern.
he / she should be sending a suitably qualified electrician to fault find, repair and test the installation.