DISTRIBUTOR CANNOT BE TRUSTED...

broadgage:

Yes, rebar can provide a good earth electrode and I would use this after testing, possibly in conjunction with metal water pipes.

I would not consider any arrangement that uses any part of the neutral system as an earth, far too much risk of an open neutral.

The other point I meant to mention is that, from an oil and gas background, I am used to designing redundancy into everything so bonding extraneous metal pipework for me would be preferable to relying on a single earth electrode connection (i.e. single point of failure).

 

mapj1:

You could take a low wattage lamp and see if you can light it between the live and the rebar - way back in the dark ages of pipe smoke and coal dust when 3 pin sockets were a new thing, a test lamp of a few tens of watts was a quick way to verify if a proposed  earth electrode or water pipe was any good at taking current to ground or not.

In a refinement to the test, you could measure the line to rebar voltage with the lamp on and off and estimate an effective electrode impedance.

Of course if it does not light, then remove it PDQ, as for the duration of the test you have made it live, and there may be some poor sod dancing about in the basement...

Thanks Mike, I love to learn the good old ways! Go easy on my setup, it is difficult to source items when you don’t have Amazon or B&Q! So… it would appear that the rebar has a very poor / no electrical connection to earth at all from the lamp test (I am trying my hardest to get a loop tester in country):

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4.jpeg   The brightness of the lamp is the same as the image 3, just the camera used makes it seem less in this shot. 
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7.jpeg
8.jpeg

 

AJJewsbury:

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.

Great! Thanks for the confirmation Andy.

AJJewsbury:

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.

So it is possible to install a new earth electrode immediately next to the water pump casing at ground level and bond the local metallic pipework (water + drainage) to it. The only place I can bond the gas pipe would be on the 4th floor (the gas pipe is tucked away in a locked location at ground level and loops around the building horizontally to each flat).

I can’t see any immediate issue with the parallel earth path between the TT earth electrode - consumer unit MET & the MET through the water pump cable armour to ground, it would help for the oversizing aspect.

I know there is no easy answer to this but what would you suggest for generous oversizing? I guess 16 mm2 won’t cut it. I fear you will say as large as possible…$$$

The plastic water and drainage is typically what would be used locally anyway into the flat. Here is another proposal utilising as much bonding as possible:

CG Project Rev02.pdf

Chris

broadgage:

Yes, rebar can provide a good earth electrode and I would use this after testing, possibly in conjunction with metal water pipes.

I would not consider any arrangement that uses any part of the neutral system as an earth, far too much risk of an open neutral.

The other point I meant to mention is that, from an oil and gas background, I am used to designing redundancy into everything so bonding extraneous metal pipework for me would be preferable to relying on a single earth electrode connection (i.e. single point of failure).

 

mapj1:

You could take a low wattage lamp and see if you can light it between the live and the rebar - way back in the dark ages of pipe smoke and coal dust when 3 pin sockets were a new thing, a test lamp of a few tens of watts was a quick way to verify if a proposed  earth electrode or water pipe was any good at taking current to ground or not.

In a refinement to the test, you could measure the line to rebar voltage with the lamp on and off and estimate an effective electrode impedance.

Of course if it does not light, then remove it PDQ, as for the duration of the test you have made it live, and there may be some poor sod dancing about in the basement...

Thanks Mike, I love to learn the good old ways! Go easy on my setup, it is difficult to source items when you don’t have Amazon or B&Q! So… it would appear that the rebar has a very poor / no electrical connection to earth at all from the lamp test (I am trying my hardest to get a loop tester in country):

3.jpeg
4.jpeg   The brightness of the lamp is the same as the image 3, just the camera used makes it seem less in this shot. 
5.jpeg
6.jpeg
7.jpeg
8.jpeg

 

AJJewsbury:

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.

Great! Thanks for the confirmation Andy.

AJJewsbury:

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.

So it is possible to install a new earth electrode immediately next to the water pump casing at ground level and bond the local metallic pipework (water + drainage) to it. The only place I can bond the gas pipe would be on the 4th floor (the gas pipe is tucked away in a locked location at ground level and loops around the building horizontally to each flat).

I can’t see any immediate issue with the parallel earth path between the TT earth electrode - consumer unit MET & the MET through the water pump cable armour to ground, it would help for the oversizing aspect.

I know there is no easy answer to this but what would you suggest for generous oversizing? I guess 16 mm2 won’t cut it. I fear you will say as large as possible…$$$

The plastic water and drainage is typically what would be used locally anyway into the flat. Here is another proposal utilising as much bonding as possible:

CG Project Rev02.pdf

Chris