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TN-C-S and TT in the same house?

jbrameld
I have across a property in Norfolk that looks like it has both TN-C-S and TT earthing.  I haven't fully investigated what is connected to what yet, but the incoming supply is on an overhead line, and there is an earthing conductor from the company head into the CU, so this is assumed TN-C-S.


When digging out for a new patio in the back garden we found a connected earth rod - just buried under the grass, no enclosure etc,  No obvious sign of that appearing at the CU either.


The property was extended around 20 years ago and the earth rod is just outside the extension at the back of the house


Incoming gas has a bond at the meter box, but I haven't yet traced if this is connected to the earth rod or to the CU.  Incoming water is also bonded but again I need to check where to.  The incoming water would have been moved from the original location when the property was built (1940s/50s at a guess) as it now appears in the rear extension.  I'm not convinced the incomer is metallic but I need to pull the washing machine out to check.  If not then no bond required anyway.


So accepting that more investigation is required, does anyone have any theories as to why we may have potentially 2 earthing systems in one house?  No powered outbuildings so no need for TT islands and I wouldn't expect an extension in the property to be done as an island.


Thanks,


Jason.
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    jbrameld:

    Thanks for the replies.  


    I'll do a bit more testing/investigating on the bonding to see what connects to what and make sure that I don't have 2 different systems and otherwise not worry about it too much.  No notices at the incomer.  There is a 30mA RCD in a separate enclosure to the old-style Wylex re-wireable fuse CU which has at least been upgraded to use the plug-in MCBs.


    Difficult to be sure, but the earth rod is 'conveniently' in a corner between the side and rear extension, and has a curly earth cable that seems to go through a hole in the extension wall, so probably put in when the extensions were done.  May be fun if it is to be retained when at a future date the location where it is sited gets built over as part of further development....


    Jason.


     


    So, as it is, just one single earth fault on just one final circuit will trip off everything. Not perhaps dangerous, but not reliable. You wouldn't want to be plunged into darkness if in the bath or shower, or half way down the stairs,  if an appliance like a washing machine become faulty and trips off the lot.


    Z.


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  • 0
    jbrameld:

    Thanks for the replies.  


    I'll do a bit more testing/investigating on the bonding to see what connects to what and make sure that I don't have 2 different systems and otherwise not worry about it too much.  No notices at the incomer.  There is a 30mA RCD in a separate enclosure to the old-style Wylex re-wireable fuse CU which has at least been upgraded to use the plug-in MCBs.


    Difficult to be sure, but the earth rod is 'conveniently' in a corner between the side and rear extension, and has a curly earth cable that seems to go through a hole in the extension wall, so probably put in when the extensions were done.  May be fun if it is to be retained when at a future date the location where it is sited gets built over as part of further development....


    Jason.


     


    So, as it is, just one single earth fault on just one final circuit will trip off everything. Not perhaps dangerous, but not reliable. You wouldn't want to be plunged into darkness if in the bath or shower, or half way down the stairs,  if an appliance like a washing machine become faulty and trips off the lot.


    Z.


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