Earthing my water supply

[mk2phil]

Hi there,

I've recently been trying to educate myself on what main/supplementry bonding is and why you need it, so I can be sure that my house is correctly protected.

I have an earth clamp on my gas main that connects to the CU. But where my water main enters the house I dont have any earth clamps at all.

Do I need to clamp the incoming water main and run an earth cable all the way back to the CU as per the gas main?

 

[ricicle]

Yes as well as any other metallic service/structure that could introduce a potential from outside the equipotential zone . For most domestic properties this will just be the two (fuel and water) and 10mm² earth wire.

 

[LoveRocket]

Yes.

 

[ColJack]

it depends.. what does your water come in as? copper, lead, plastic?
if it's plastic then you don't need to

 

[riveralt]

it depends.. what does your water come in as? copper, lead, plastic?
if it's plastic then you don't need to

If your water comes in any of the above you will still need to earth your supply if it becomes copper once it enters the house. 10mm2 cable within 600mm of it entering the house.

 

[Paul_C]

it depends.. what does your water come in as? copper, lead, plastic?
if it's plastic then you don't need to

What the supply pipe material happens to be is immaterial. If it's copper piping thoughout the house, then it should be bonded, regardless of whether the supply line is plastic or metallic.

 

[ban-all-sheds]

Not that that makes any engineering sense whatsoever.

 

[ColJack]

how on earth is a plastic pipe in the ground supposed to introduce an earth potential that may differ from the electrical earth potential in the equipotential zone?

bonding of pipes in a bathroom for reasons of equipotential is a different matter to main earths..

 

[Paul_C]

A plastic pipe won't introduce any potential, but a fault which causes that pipework to become live at one point will result in that potential appearing on the rest of the pipework all around the house if it isn't bonded.

 

[ColJack]

by bonding the copper that's fed by plastic you are in fact increasing the danger of a shock..
if it's not earthed and you happen to be touching a pipe and a live wire then there if no path to earth and in theory you wouldn't get a shock..
by earthing the copper you are providing a path to earth.

under this rationale I need to earth all of the steel door frames in my mothers house and the aluminium patio doors then?

the idea of the main bonding is to tie all of the things that are introducing an earth potential together at the same potential.

 

[Spark123]

I can see why you wouldn't expect to need to bond copper pipes fed by plastic as the plastic should provide adequate insulation hence the copper shouldn't be classed as extraneous hence needs bonding.
To ensure something isn't extraneous you can do resistance measurements, iirc if the resistance is greater than 22K ohms with respect to the MET then it doesn't need bonding.
Hopefully your window frames and patio doors won't be extraneous, however copper pipework may be.

 

[ColJack]

A plastic pipe won't introduce any potential, but a fault which causes that pipework to become live at one point will result in that potential appearing on the rest of the pipework all around the house if it isn't bonded.

then why pray tell do we not have to bond kitchen sinks anymore?
if there is a fault which results in the metal kitchen sink becoming live then that's the same thing..

as I said, supplimentary bonding in bathrooms etc is a different thing..

with the more prolific use of RCD's nowadays you don't even have to bond the metalwork in the bathrooms together so it's entirely possible that the metal bath can become live and not bonded to anything..
the RCD takes care of that.

 

[Paul_C]

There's a difference between a metal window frame which is confined to a specific area and a metallic piping system which runs throughout several different rooms of the house, and will be almost impossible to segregate completely from electrical services.

Even without bonding it's likely that in the typical British house there will be enough stray parallel paths to earth via pipes clipped to mortar, copper cylinders resting on brick piers, etc. to make the resistance to earth sufficiently low to make shock between the pipework and a live conductor highly probable anyway. Unless there are insulating plastic couplings involved, it's likely that the pipework will be earthed indirectly via the immersion heater or boiler.

As for the supplementary bonding and RCD issue, I take that as being part of the overall craziness of the 17th edition which is why as far as I'm concerned the Regs. are gradually becoming more and more silly, imposing things like RCD protection on buried cables while abandoning long-recognized bonding issues.

Remember that whatever watered-down rules the 17th edition might have about bonding water systems, the Regs. used to make it quite clear that such bonding was required.

 

[ColJack]

There's a difference between a metal window frame which is confined to a specific area and a metallic piping system which runs throughout several different rooms of the house, and will be almost impossible to segregate completely from electrical services.

true, but I've much more chance to come into contact with the metal door frames than I do the pipework that it under the floors, and behind kitchen units don't i?

Even without bonding it's likely that in the typical British house there will be enough stray parallel paths to earth via pipes clipped to mortar, copper cylinders resting on brick piers, etc. to make the resistance to earth sufficiently low to make shock between the pipework and a live conductor highly probable anyway.

what kind of dodgy plumbers do you use? all of my copper pipes are clipped to the wall with plastic clips that space it off the wall by about 5mm.. no contact at all with the wall.. the immersion cylinder is on timbers usually also..

Unless there are insulating plastic couplings involved, it's likely that the pipework will be earthed indirectly via the immersion heater or boiler.

true and kind of the point I am making.. it's probably already suplimentary bonded which is all it needs, doesn't need a main earth bonding as well..

As for the supplementary bonding and RCD issue, I take that as being part of the overall craziness of the 17th edition which is why as far as I'm concerned the Regs. are gradually becoming more and more silly, imposing things like RCD protection on buried cables while abandoning long-recognized bonding issues.

Remember that whatever watered-down rules the 17th edition might have about bonding water systems, the Regs. used to make it quite clear that such bonding was required.

your one of the old school I see.. so should we still abide by the first regulations then? or have a man with a white flag walking in front of our motor vehicles and restrict them to 5 miles an hour like they used to be?
as things improve and more modern safety measures are available then the rules have to change to reflect that.
you personal dislike of the newer regs doesn't make them any less valid, or the old regs any more valid..

 

[riveralt]

Hi there,

I've recently been trying to educate myself on what main/supplementry bonding is and why you need it, so I can be sure that my house is correctly protected.

I have an earth clamp on my gas main that connects to the CU. But where my water main enters the house I dont have any earth clamps at all.

Do I need to clamp the incoming water main and run an earth cable all the way back to the CU as per the gas main?

To bring us back to the OP's original point:

Several people have already correctly said you should run an earth cable back to the MET. The debate that followed should not distract you from following their advice.

Outlined below is the relevant section from the Electricians guide to the Building Regulations:

"In each installation, main protective bonding conductors are required to connect to the main earthing terminal, extraneous conductive parts, inlcuding:
water service pipes
gas installation pipes
other service pipes (eg oil) and ducting
central hearting and air conditioning systems
exposed metallic structural parts of the building.
lighting protection systems"

Plastic supply pipes

"There is NO requirement to main bond an incoming service where both the incoming supply pipe and the pipework within the installation are both of plastic. Where there is a plastic incoming service and a metal installation within the premises , main bonding may be needed and in such cases the main boding conductors should be connected on the customers side of any meter, main stop cock or insulating insert."