earthing (to?) copper pipes

[Tobiasisno1]

Hi. We're having our kitchen refitted and in preparation had some electrical work done. The electrician ran a new earth to the house side of the stop tap, within 600mm of the incoming main, but when the kitchen fitters came they moved stop tap too far from the main, so repositioned the earth to the main itself and used plastic pipe for the alterations.

I've done a search on here and am thoroughly confused-is it ok to connect the earth direct to the main, before the stop tap, and is it now necessary to run another earth to the copper pipe as presumably the plastic pipe used means the kitchen pipework, and I suppose the rest of the house pipework isn't earthed?

All replies gratefully accepted, but keep them simple, please.

thanks,
Keith

 

[bernardgreen]

and I suppose the rest of the house pipework isn't earthed?

In the places where electricity and pipe work come into close proximity the electrical earth will earth the pipe work. Items such as immersion heaters and gas boilers with electrical control are earthed via the CPC ( earth wire ) in their supply cables.

All replies gratefully accepted, but keep them simple, please. thanks, Keith

Until the MeerKats take over the world there will never be a simple way to explain the difference between "earthing" and "bonding". Electrically in a domestic installation they are the same thing but the regulations treat them as two very different things.

( except of course for the now illegal voltage operated earth leakage breakers on TT supplies where the earth wire was not earth and bonding anything in the house to real earth could prevent the safety device from working )

 

[ricicle]

there will never be a simple way to explain the difference between "earthing" and "bonding". Electrically in a domestic installation they are the same thing

No they are not Bernard, as we keep having to explain time and time again to those with no understanding of it.

 

[holmslaw]

..

 

[Tobiasisno1]

there will never be a simple way to explain the difference between "earthing" and "bonding". Electrically in a domestic installation they are the same thing [/quote]

No they are not Bernard, as we keep having to explain time and time again to those with no understanding of it.[/quote]

Which is why I asked for "simple" replies, chaps!! Can you just tell me please, do I need another earth wire to the copper pipe and is it OK to fix an earth direct to the incoming main, which I think is steel rather than lead?

Keith

 

[bernardgreen]

No they are not Bernard, as we keep having to explain time and time again to those with no understanding of it.

Original poster, you can ignore the rest of this as what you have in your house appears to be safe.


Ricicle

In the regulations they have different names as they serve different purposes.

But as equi-potentially bonding pipe work to the MET ( main earth terminal ? ) connects the pipe work to the "earth" of the system it is also electrically "earthing" the pipe work. So electrically they are the same unless the impedances in the bond/earth cables are high enough to create significant voltage drops when current flows to or from earth.

That said there are cases where there can be high currents flowing in bonding when a PME "earth" derived from incoming neutral is not at true ground and the incoming water supply is a metallic supply with a very low impedance to ground.

Hence a CPC can have a CSA of 1 mm as it only has to carry 35 ma to trip an RCD or the trip current of a MCB for a very short length of time. With effective protection in place it should never be carrying excess current long enough to heat up enough to melt.

The bond wire between the MET and a pipe in good contact with ground may have to continuously carry the current from an un-balanced or open circuit network neutral for as long as it take to detect and then repair the fault. Turning of the supply at the main switch will not stop that current. Hence the need to use at least CSA 10mm for bonding MET to incoming pipe work.

 

[Tobiasisno1]

Original poster, you can ignore the rest of this as what you have in your house appears to be safe.

Thanks, Bernard, and to you, Holmslaw, thats what I wanted to know.

Keith

 

[holmslaw]

..

 

[bernardgreen]

I accept that it was a reckless statement to make without having seen and tested the system.

 

[ricicle]

Electrically in a domestic installation they are the same thing

In the regulations they have different names as they serve different purposes.

 

[JohnW2]

(again, not for the original poster!)

That said there are cases where there can be high currents flowing in bonding when a PME "earth" derived from incoming neutral is not at true ground and the incoming water supply is a metallic supply with a very low impedance to ground.

Hence a CPC can have a CSA of 1 mm as it only has to carry 35 ma to trip an RCD or the trip current of a MCB for a very short length of time. With effective protection in place it should never be carrying excess current long enough to heat up enough to melt.

The bond wire between the MET and a pipe in good contact with ground may have to continuously carry the current from an un-balanced or open circuit network neutral for as long as it take to detect and then repair the fault. Turning of the supply at the main switch will not stop that current. Hence the need to use at least CSA 10mm for bonding MET to incoming pipe work.

That's a good summary - in relation to TN-S or TN-C-S situations. However, as I have said on a number of occasions, I really don't see that the same argument can sensibly be applied to TT systems. Unlike the potentially dramatically different situation with DNO-provided earth terminals, the chances of a TT earth electrode introducing a low impedence significant non-earth potential are vanishingly small, so there really is virtually no possibility that the bond between MET and incoming services would ever have to carry any appreciable current for an appreciable period of time (really only part of fault currents, for a very brief period {until RCD or MCB operates}, if the incoming pipes provide a lower impedance eath path than does the earth electrode). To my mind, that means that such a bond in a TT system is essentially a 'supplementary (equipotential) bond', and that the bonding cable should not really need to be sized to carry large currents for appreciable periods of time.

Of course, the irony is that in most TT systems, the incoming water pipes probably provide a much lower impedance path to earth than does the earth electrode and therefore (in the presence of a substantial MPB conductor) effectively become 'the earth'. However, since the regs do not (for good reason) allow one to rely on such an earth, that would not be a valid reason for requiring a large CSA conductor between MET and incoming service pipes.

That's how I see it, anyway.

Kindest Regards, John