UK Earthing Arrangement

[Tonychitty]

Can anyone help, i had a new combi boiler fitted last year and they used mainly plastic fittings to make there connections, i have attached a photo below my question is where should my 10mm earth bond go , the incoming water pipe is made of lead, do i simply bond the 10mm earth to the incoming water pipe with a suitable clamp and then bridge the plastic plumbing tee to the nearest copper pipe.
any feedback would be mostly appreciated

 

[Pretty Mouth]

TonyChitty, here's how I like to think about it:

Think about the path the current would take if a human were to receive a shock while simultaneously touching an exposed conductive part, and an (unbonded) extraneous metal pipe, while a fault to earth occurred.

From the transformer, the current would pass through:
1 - Line conductor
2 - Faulty exposed conductive part
3 - Human
4 - Metal pipe
5 - Metal pipe at point of entry to building
6 - General mass of earth
7 - Neutral pole of transformer.

Without bonding, there is a large potential difference between point 2 and 4, so the human gets a shock.

By bonding the metal pipe at the point of entry to the building, the potential between point 2 and point 5 are equal if an earth fault occurs. No current will flow between these points, and the human is safe.

This is why we bond at the point the point the pipe enters the building - it doesn't matter what you put between points 4 and 5 - plastic joints, pipework, and so on - the potential between 2 and 5, and everything in between, is still equal, so no current flows between these points.

 

[Tonychitty]

TonyChitty, here's how I like to think about it:

Think about the path the current would take if a human were to receive a shock while simultaneously touching an exposed conductive part, and an (unbonded) extraneous metal pipe, while a fault to earth occurred.

From the transformer, the current would pass through:
1 - Line conductor
2 - Faulty exposed conductive part
3 - Human
4 - Metal pipe
5 - Metal pipe at point of entry to building
6 - General mass of earth
7 - Neutral pole of transformer.

Without bonding, there is a large potential difference between point 2 and 4, so the human gets a shock.

By bonding the metal pipe at the point of entry to the building, the potential between point 2 and point 5 are equal if an earth fault occurs. No current will flow between these points, and the human is safe.

This is why we bond at the point the point the pipe enters the building - it doesn't matter what you put between points 4 and 5 - plastic joints, pipework, and so on - the potential between 2 and 5, and everything in between, is still equal, so no current flows between these points.

I'll try and shed some light for you.
In the event of a fault on your electrical system conductive parts (ie earthed metal parts of the electrical installation such as a metal light fitting or washing machine case) may experience a rise in potential relative to the general mass of earth which is at zero volts or thereabouts. Within a building that rise in potential is unlikely to be a serious hazard because a person in contact with a conductive part during the fault is likely to be stood on an electrically insulating surface such as a wooden floor. However the metallic water service is in contact with the general mass of earth and will introduce that potential into the building. Now there is a hazard because a person may be in contact with both a conductive part and the water service at the same time the fault is in progress and subject to a shock. By bonding both together the possibility of a potential difference is reduced. Where there is an insulating section immediately after the water service enters the property the rest of the copper pipework in the house has effectively been disconnected from the general mass of earth and so does not require bonding because it can no longer introduce an earth potential.
In your case the rest of the house pipework is isolated from the earth potential by the plastic joint, only the short section of lead and the filter are extraneous. As Tel stated what are the chances of contact between that and a conductive part for the duration of a fault? If you think there is then bond the lead. But you DO NOT NEED TO BOND THE REST OF THE PIPEWORK AFTER THE PLASTIC JOINT. In fact doing so may actually increase the shock risk in the event of a fault.
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NO!

if i do bond the lead pipe back to the MET am i not in theory reconnecting the extraneous part back into the system any way as my gas pipe is also connected to it and with the combination boiler all supplementry bonded together all the copper will be connected anyway

 

[radiohead]

There's no reason not to bond both the lead and copper if that's what you want to do. My contention is that it is not required to bond the copper past the plastic joint, and debatable whether there is sufficient extraneous lead present even for that to be required. But if you feel the need go ahead, it wont do any harm.

 

[Tonychitty]

There's no reason not to bond both the lead and copper if that's what you want to do. My contention is that it is not required to bond the copper past the plastic joint, and debatable whether there is sufficient extraneous lead present even for that to be required. But if you feel the need go ahead, it wont do any harm.

Thanks for explaining this to me in great detail thankyou and everyone that replied to my original post.

 

[DPG]

Good debate this one.