question for ericmark

[securespark]

You always beat me to it, although to be fair, I am at least an hour late...

Yes, I think westie works for ENWL, what was Norweb.

I worked in many areas, but mostly in that area. AFAICT, they were always reluctant to PME a TT install that was part (for example) of a row of terraces or cottages without PME'ing the lot. But (again AFAICT), that was their only restriction as regards "mix and match".

As you say, he'll no doubt be along shortly to put us all right!

 

[JohnW2]

I worked in many areas, but mostly in that area. AFAICT, they were always reluctant to PME a TT install that was part (for example) of a row of terraces or cottages without PME'ing the lot.

That is, of course, a somewhat different matter, and probably quite reasonable, given the potential safety issues of having TT and PME installations in very close proximity. As I recently said/implied in relation to bernard's installation, I'm a little surprised that the DNO was happy to PME only half of a building (the other half still being TT) and, knowing his views about TN-C-S, even more surprised that bernard chose to take up the offer of PME.

But (again AFAICT), that was their only restriction as regards "mix and match".

It seems to be the mixing of TN-S and TN-C-S on the same substation that Lectrician was talking about.

Kind Regards, John

 

[bernardgreen]

so I'm a little surprised you didn't stick with TT for your cottage, particularly given the potential complications associated with having a TT installation in the other half of the building. I wonder what you reasoning was.

Getting power into the cottage was a priority and planning and installing an adequate ground rod installation would have delayed that.

I could not use the ground rod of the retail unit.

I am still considering changing to a TT if there are problems of significant voltages between "earth" and ground as the walls are rubble and mortar and conductive so they import ground into the equipotential area albeit at a high impedance .

I am not too concerned about using PME at this location as the underground street cable between cottage and substation is about 100 metres long and relatively new so the risk of a neutral failure is very small. At the previous house the supply was part ancient underground cable and part very old overhead so the neutral was at significant risk of failing.

 

[JohnW2]

Getting power into the cottage was a priority and planning and installing an adequate ground rod installation would have delayed that. I could not use the ground rod of the retail unit.

Fair enough. You must have a very efficient DNO - I would have expected there to be enough time to install fifty 'adequate earth rods' whilst waiting for them to turn up to provide a new supply

I am still considering changing to a TT if there are problems of significant voltages between "earth" and ground as the walls are rubble and mortar and conductive so they import ground into the equipotential area albeit at a high impedance .

Again, fair enough.

Of course, if there are other fairly close properties with PME, and if service supply pipes are metal, then you might not have much of a choice, electrically-speaking. You could end up like me with a TT installation which has a Ze of around 0.3Ω, thanks (I presume) to the neighbour's PME and a metal water supply connection between the houses which is main bonded at both ends - i.e. effectively PME, whether I want it or not! The earth rod itself is usually about 75Ω. Even if I remove the main bonding in my house, the Ze is still not more than about 0.4Ω, presumably due to incidental connections between CPCs and the water supply pipe.

Kind Rregards, John