Earthing after water service replacement

[--tom]

what earthing/bonding is typically necessary after metal water service is replaced with plastic.
The main elec service, in this case, has 3no earth clamps to a very old lead and fibre kind of wrapping.

 

[ban-all-sheds]

what earthing/bonding is typically necessary after metal water service is replaced with plastic.

Same as before.

//www.diynot.com/wiki/electrics:earthing-supply-types-and-bonding

The main elec service, in this case, has 3no earth clamps to a very old lead and fibre kind of wrapping.

TN-S supply? //www.diynot.com/wiki/electrics:earthing-arrangements

And 3 clamps? Where do the cables from them go?

 

[ColJack]

I take it you mean that the water supply pipe is plastic now and not the internal pipes?

no need to bond it if it comes in in plastic as it's not capable of introducing an earth potential..

 

[securespark]

Can you clarify that, Col??

 

[ColJack]

what's to clarify?

a plastic supply pipe cannot introduce an earth potential into the equipotential zone and so does not require to be bonded to all the bits of buried metal that come into the equipotential zone.

 

[--tom]

Thank you for the info.
The three bonding cables 1. goes to C/U - 10mm
2. goes to, i think, cant see, the gas -6mm
3. goes to in-situ metal water supply( it looks like its been run in 2.5mm)
So, if i understand, i should now bond (in 10mm) the remaining Cu water pipes into the ... ? I hesitate to touch the degraded looking main supply.

 

[chimp]

You should bond the incoming water server within 600mm of it entering the property or consumer side of the meter. If the supply is plastic then you should bond at the first point it becomes metal if any.

The bonding size will depend on the earthing system and incoming supply size.

 

[bernardgreen]

a plastic supply pipe cannot introduce an earth potential into the equipotential zone

Plastic pipe cannot conduct but the water in the pipe can, depending on the levels of added flourine, chlorine and naturally occuring dissolved chemicals all tap water is conductive to some extent. If the pipe is plastic all the way to the metal tap and stainless steel sink then via the water an earth potential can be introduced at the sink within the equipotential zone. Hence bonding at the taps may be a good idea.

 

[ColJack]

if it's INSIDE the plastic pipe, how does it come into contact with earth?

get a 1m length of hosepipe, fill it with water and stick your megger in each end set at 250V.. see what its resistance is..

it's not an earth potential if it's several hundred ohms above earth due to the length of the plastic pipe before it encounters some metal to conduct to earth

4.7 in the OSG says no need to bond metalic parts supplied by plastic pipes..

 

[Spark123]

4.7 is about "Supplementary Bonding"

4.4 says for a plastic incoming service and metal installation within the premises main bonding is recommended unless it has been confirmed that any metal pipework within the building is not introducing earth potential.

 

[bernardgreen]

if it's INSIDE the plastic pipe, how does it come into contact with earth?

from next doors earthed metal pipe work. And the big pump in the water works.

get a 1m length of hosepipe, fill it with water and stick your megger in each end set at 250V.. see what its resistance is..

Would you stand on an insulated mat, hold a bare live wire in one hand and put your other hand under the water from a hose pipe and feel totally safe. ? DO NOT TRY THAT

it's not an earth potential if it's several hundred ohms above earth due to the length of the plastic pipe before it encounters some metal to conduct to earth

In the extreme case of a Live to sink fault ( defective waste disposal unit )230 volts divided by 460 ohms is half an amp. or 120 watts heating water in the pipe.

4.7 in the OSG says no need to bond metalic parts supplied by plastic pipes..

Take that " water is non conductive " idea to extremes and it would suggest that there is no problem with water and electrics coming into contact with each other, switches and sockets in bath rooms should then be acceptable when the bath and pipe work are all plastic.

 

[Spark123]

Water in it's pure form is non-conductive which is why it is used in batteries, it is the impurities in water which make it conduct.
This means that the conductance of water changes from area to area, and if you are unlucky enough to have to try and measure the level of pure water water using conductivity probes then you'll that it isn't straight forwards!

The resistance of impure water also changes as the usage changes, such as a heating system with a double does of inhibitor in a 15mm plastic pipe can have a resistance of 20Kohms/m @ 60ºc and tap water 115Kohms/m.
If the pipework size is increased these resistance will drop.

Although slightly outdated now, there is an interesting article here on the matter: www.theiet.org/publishing/wiring-regulations/mag/pre-2004/pre14-earthing-plastic-pipes.cfm?type=pdf