DISTRIBUTOR CANNOT BE TRUSTED...

It will be near impossible to install a new TT earth electrode in the car park / yard away from underground metalwork. I need to continue my homework on rebar electrodes and distances away from other buried services. Would it be such an issue in a flat with no extraneous connections for the TT earth electrode to be in close proximity to buried metal work? If a fault from another system were to raise the ground potential then all the exposed metalwork in the flat should also raise to the same potential i.e. no potential difference between exposed metalwork within the flat.

The idea of keeping a TT earth separate from other earthing systems generally only applies where there's something about the other earthing system you wish to avoid - e,g. avoiding the dangers of PME earths when supplying caravans or EV charge points.


If the other hand you're only using a TT system because a supplier's earth terminal isn't available (otherwise PME would have been fine) then there's little need to worry about segregating your earthing arrangements. Indeed it's quite common to have rural TT installations that have TN-like Zs values because there's a path via bonding to metallic water or gas pipes to a TN neighbour.


As you say, if you can create an equipotential zone, the actual potential it is at is far less of a worry. In practice you can never create a perfect equipotential zone (especially if bits of the installation go outside!) But it seems you're in a far from ideal starting position so I think the best you can go is find some kind of reliable Earthing facility (local electrode or re-bar) and then bond everything within reach - including things that might be connected the dodgy supply 'Earth' if needs be. As far as possible using Class II equipment outdoors at ground level - or protected by insulating enclosures - can mitigate the risks there. Or you might consider a separated circuit for things like the water pump (i.e. unearthed, fed via an isolating transformer) - although if the pipework is metallic, it's probably pointless.


Just bare in mind that if yours is the only installation in the area that does have proper bonds and the supply N/PEN does go faulty, you might end up carrying the return currents for most of the neighbourhood through your bonds - so generous oversizing might be the order of the day. Plastic plumbing can certainly help.


   - Andy.

It will be near impossible to install a new TT earth electrode in the car park / yard away from underground metalwork. I need to continue my homework on rebar electrodes and distances away from other buried services. Would it be such an issue in a flat with no extraneous connections for the TT earth electrode to be in close proximity to buried metal work? If a fault from another system were to raise the ground potential then all the exposed metalwork in the flat should also raise to the same potential i.e. no potential difference between exposed metalwork within the flat.

The idea of keeping a TT earth separate from other earthing systems generally only applies where there's something about the other earthing system you wish to avoid - e,g. avoiding the dangers of PME earths when supplying caravans or EV charge points.


If the other hand you're only using a TT system because a supplier's earth terminal isn't available (otherwise PME would have been fine) then there's little need to worry about segregating your earthing arrangements. Indeed it's quite common to have rural TT installations that have TN-like Zs values because there's a path via bonding to metallic water or gas pipes to a TN neighbour.


As you say, if you can create an equipotential zone, the actual potential it is at is far less of a worry. In practice you can never create a perfect equipotential zone (especially if bits of the installation go outside!) But it seems you're in a far from ideal starting position so I think the best you can go is find some kind of reliable Earthing facility (local electrode or re-bar) and then bond everything within reach - including things that might be connected the dodgy supply 'Earth' if needs be. As far as possible using Class II equipment outdoors at ground level - or protected by insulating enclosures - can mitigate the risks there. Or you might consider a separated circuit for things like the water pump (i.e. unearthed, fed via an isolating transformer) - although if the pipework is metallic, it's probably pointless.


Just bare in mind that if yours is the only installation in the area that does have proper bonds and the supply N/PEN does go faulty, you might end up carrying the return currents for most of the neighbourhood through your bonds - so generous oversizing might be the order of the day. Plastic plumbing can certainly help.


   - Andy.