Water Pipe earth bonding ... ?

[Arfa Daily]

I'm in the process of doing a complete refit on my downstairs cloakroom. The cold water rising main comes up into that room, and has the main household stop-tap on it right where it emerges from the floor. Just beyond that point, a thick earth bonding wire is attached. This disappears through the wall to the garage, where the consumer unit is located, just the other side of that wall. All OK so far. However, when I took out the existing basin, right up underneath it, just below the taps, the hot and cold pipes were bonded together with another quite thick wire. It didn't go anywhere else. Just between the two pipes. I'd never seen this done before, and certainly not on any of the other hot and cold pipes around the house - there's a shower room and a bathroom upstairs, both of which I've fully refitted. Is this normal practice - or was it 25 years ago when the house was built ? - and if so, what is the thinking behind it, or need for it ? As I am replacing the basin with one that has a single hole for a monobloc mixing tap, I will not be reinstating this wire as a separate entity, as the two pipes should be firmly rebonded together via the tap body itself. Anyone see a problem with my thinking ?

Arfa

[John Rumm]

Yup, sounds normal for a main equipotential bond. The wire ought to be

10mm^2 if you have TN-S or TN-C-S earthing.

That sounds like a supplementary equipotential bond.

Yes its is normal practice, but is actually only required in a room with a bath or shower. So it is not required in your cloakroom.

The idea is that in locations where you are at increased risk from electric shock (i.e. you may be wet, naked, barefoot etc), the supplementary bonding creates an equipotential zone.

So unlike earthing, it is not designed to cause disconnection of a circuit, or to limit the touch voltage on any metal parts you come into contact with. It is simply designed to electrically tie together anything conductive that could introduce a voltage into the room. So pipework, circuits, electrical appliances etc are all joined together via protective conductors, such that if anything becomes live, then it

*all* becomes live. The logic being that the absolute voltage that you can come into contact with is not actually that important, what matters is the voltage difference that you can make contact with.

For more detail see:

with one that has a single hole for a monobloc mixing tap, I will not be

If the basin is in the cloakroom, (i.e. no bath or shower) then there is no need to replace it at all. If it were in a bathroom, then you would usually bond the tails of the tap where they go back to 15mm pipe, and these would also connect to any CH pipes in the room, other taps, metal waste pipes if present, and the earth wires of any circuits that are used in room.

(note that under the 17th edition, you can omit supplementary bonding altogether so long as the main equipotential bonds in the house to the incoming services etc are in place, and all the circuits that feed the bat/shower room are protected by a RCD with a trip current of

[chris French]

Absolute rubbish Harry :-)

[Tim Watts]

harry ( [e-mail]) wibbled on Monday 24 January 2011 07:52:

Assuming the cloakroom does not contain a bath or shower, it is not a special location and therefore does not require supplimentary bonding (this is the strap between the basin pipes).

However, its presence does not harm in this case.

The other earth cable running back to the CU is main bonding and of course, that must remain.

There was a phase in about the timeframe the OP described where bonding was not well understood and people were bonding kitchen sinks, metal radiator covers and all sorts needlessly.

It should also be noted that supplimentary bonding in special locations contain a bath or shower is no longer required under the 17th provided various other conditions are met.

[cynic]

SNIP

Encouraged by everyone with a partial understanding of the requirements of the regulations and IMHO due to the presence of the cable manufacturers being represented on the wiring regulations committee. What a marvellous way to create a very substantial market for copper wire!

[Arfa Daily]

Thanks all for the explanations. Makes a deal of sense now I'm looking at it from a slightly different viewpoint.

Arfa

[Andy Wade]

I once heard of a case where someone had bonded each and every coat hook in a school cloakroom :~)

[Skipweasel]

Yebbut that's to stop the little scrotes from nicking them.