Discuss Bonding water services when plastic pipes are present in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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ashlec

Hi All,
ive been working in a old 50's/60's property which has a black pvc/almost rubber water pipe incoming to the stopcock, then it leaves the sc in the same type of pipe
then disappears into a box section going upstairs under the floor . Now the other end could be anywhere but i can't find it, we all know it should be within 600mm & before the first branch etc
but in this case its not going to happen.

My question is there is a 6mm earth going from the MET to the cold ( everywhere else is copper pipe ) in the bathroom linked to the hot & all the 4mm sup bonding is in
position ( Allready there ) & a new 17th edition board is fitted, it is a TNS system so this should be exceptable according to reg 544.1.1 , do we agree ?
I quizzed the NIC tech about it, he was saying i needed to use the adiabatic equation to work it out to see if it is sufficient enough, i've done this for main earth before
where the earth is sweated on the incoming cable but never for a services bond any ideas ?

All help will be much appreciated
 

malcolmsanford

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Your telling me the NIC tech desk as advised you to use the Adiabatic for protective Bonding conductors or for a protective conductor ................... if he was referring to protective bonding conductors then words fail me

You need to tell us why we are bonding metal work, can I ask why do you think we bond metalwork/services?
 

Amp David

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The NIC tech boy doesn't know what he's on about then, as the adiabatic is not to be used for sizing bonding conductors.

If there is a new CU with all circuits protected by RCD then forget about the supp bonding.

If needed the bonding should go ideally within 600mm of the service entering the building or within 600mm from where it is copper.

Test the service first to see if you require it in the first pace.
 

DNS1

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If all the metal pipework is internal, it's completely isolated from earth so doesn't need bonding at all does it?

That's my understanding of it.

I'd check to make sure the copper pipework doesn't earth at any point though (eg: buried in the garden for outside tap)
 
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E

Edd

This question is gona become asked more and more as plastic is becoming more popular. Basicly if the incoming is in pvc then no bond is required.
we are trying to stop an external Earth path being brought into the house that is diffrent from the Electrical earth. No external Earth path No bond required. (I know theres more to it than that, please feel free too go indepth)
 

Amp David

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Just test to see if its needed. Its the only way to know 100%.

No other way to do it
 

valleybilly

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Any internal metal pipe work can produce an earth potential inside a building ( see G3 ) witch advises/recommends bonding regardless of incoming services being plastic , A bond will be present on the water pipe via gas connection ,, the problem is when the boiler is removed braking the connection
 
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Engineer54

Any internal metal pipe work can produce an earth potential inside a building ( see G3 ) witch advises/recommends bonding regardless of incoming services being plastic , A bond will be present on the water pipe via gas connection ,, the problem is when the boiler is removed braking the connection
I wouldn't take that GN3 advise as gospel, it is unlikely that pipework would meet extraneous conductive part criteria. What this GN is indicating, is earthing rather than bonding, which in a domestic situation i wouldn't find at all necessary. The boiler will be earthed anyway, via it's electrical connection...

However, (without opening a can of worms again) there are going to be situations where bonding metal service pipework etc, WILL be necessary, even when the service supply to the building is in plastic, so it's not a hard and fast rule across the board. Consider apartment blocks for example. But generally, for individual houses etc, plastic service incomers won't require any internal metal pipework being bonded.

The very best solution if in any doubt at all, is to Always conduct your own tests, better still make those tests mandatory on every job you undertake. ...Can't really go too far wrong then, can you!! lol!!!
 

oldtimer

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Also in this can of worms say you have earthed the water and the gas incomers and the DNOs turn up 2 years later and change the supply pipes to plastic . Or say you are doing a CU change and the gas or the water pipe is plastic but internal to the house is metal so say you do not earth bond the gas because its supply pipe is plastic yet this pipe will still be earthed through the bonded water pipe via the CH boiler ie "Electrically & Mechanically sound" from the 14th
 

Deleted member 9648

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One point about testing to find out if metal pipework fed by a plastic incomer is extraneous is that it's not that easy in practice. There are liable to be loads of parallel paths in practice which may be very hard to isolate......chances are an unbonded service will be at the same potential as the electrical earthing system anyway due to these parallel paths.
 

rich.250

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One point about testing to find out if metal pipework fed by a plastic incomer is extraneous is that it's not that easy in practice. There are liable to be loads of parallel paths in practice which may be very hard to isolate......chances are an unbonded service will be at the same potential as the electrical earthing system anyway due to these parallel paths.
I would isolate supply and remove main earth as for a Ze test. In turn removes all parallel paths from
Within the building, continuity test from this removed earth to the service.
Job done. :)
 
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R

Rauer

What are you actually doing in the property as There is a note at the front of each edition of BS7671, stating : "Existing installations that have been installed in accordance with earlier editions of the Regulations may not comply with this edition in every respect. This does not necessarily mean that they are unsafe for continued use or require upgrading." and then if you look at 132.16 it states that it must be adequate
 
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Engineer54

I would isolate supply and remove main earth as for a Ze test. In turn removes all parallel paths from
Within the building, continuity test from this removed earth to the service.
Job done. :)
Why do you think that all parallel earth paths within a building always originate from the main incoming electrical earth??
 

Deleted member 9648

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I would isolate supply and remove main earth as for a Ze test. In turn removes all parallel paths from
Within the building, continuity test from this removed earth to the service.
Job done. :)
What E54 says ^^^......could be a path from a gas service to the boiler....sructural steel etc,I always feel with this test that it's hard to be completly certain you are not being misled.
 

rich.250

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I didn't mean they originate there. Just it removes all cpcs out of the question, I.e to the boiler,immersion etc where confusion can be found.
 

malcolmsanford

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What E54 says ^^^......could be a path from a gas service to the boiler....sructural steel etc,I always feel with this test that it's hard to be completly certain you are not being misled.
When rich posted that he disconnected the Main earth when doing the 23Kohm test I asked why and understand why he did, but on thinking this over not sure if perhaps it is the right course.

We disconnect the main earth conductor for a Ze in order to prove an external earth path without parallel paths, but like a measured Zs I think that measuring a piece of metal work to prove it's an extraneous conductive part should be done with these paths in place. Because in my mind to prove this metal is an ECP should be done when the installation is "As-Is" not "How-Should" be.

I've argued this before, on here and off, when told a Zs should be calculated and not measured because of parallel paths, but my answer always is, You only get an electrical fault when an installation/circuit is LIVE, and I therefore when it is in use. So I want to know the condition and therefore the value of the Zs when the installation is in use. When a fault happens, the installation/circuit don't say hold on a second lads I need to disconnect all these parallel paths and make sure I can trip the OPD without them.

Yes I agree that perhaps 2 years down the line something can change within the installation, say removing a metallic service to a non metallic one, and those paths are removed, but I have never advocated designing an installation/circuit to rely on parallel paths, but it should be designed to trip the OPD without the paths. In my view these paths are literally a bonus.

So therefore the same with an ECP, I personally think by removing the main earth and those parallel paths your giving the installation a "false" state. The reason we do bond is to bring all these metallic services into the zone at the same potential. by removing your major source of earth aren't you removing your main reference point?
 

johnboy6083

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The problem could be though malc: in a PME scenario, you could do the 23k ohm test with everything connected, and get a sufficiently low reading that you think its bonded. In fact, you could be relying on a 1mm conductor to carry diverted neutral currents.

I try to work on the basis that if I can find it I'll test it, if I can't find it then I'll pull a new bonding conductor in. I'm all for using structural steel ect though!
 

yellowvanman

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I quizzed the NIC tech about it, he was saying i needed to use the adiabatic equation to work it out to see if it is sufficient enough, i've done this for main earth before
where the earth is sweated on the incoming cable but never for a services bond any ideas ?
I can see where the NIC guy is coming from. If you work out the main earth conductor size using the adiabatic, then the bonding conductor should be not less than half that and not less than 6mm. (544.1.1)

So if you get a minimum value of 11mm for your main earth (in which case 16mm should be installed) then min size of bonding would be 6mm as half 11mm is 5.5! This assumes that its not TNCS.
 

oldtimer

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This is indeed a can of worms even if you disconnect all earths you can still get a low reading from the guy upstairs if you live in a flat ie his metal pipework could be exporting an earth to you through the pipework one other thing to note is that a property can lose an earth when they change say the gas/water supply pipes because they have no earth but they do earth bonding on the gas water hence they borrow an earth from next door this is becoming more common
 

rich.250

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The problem could be though malc: in a PME scenario, you could do the 23k ohm test with everything connected, and get a sufficiently low reading that you think its bonded. In fact, you could be relying on a 1mm conductor to carry diverted neutral currents.

I try to work on the basis that if I can find it I'll test it, if I can't find it then I'll pull a new bonding conductor in. I'm all for using structural steel ect though!
Yes I agree, if you can't find the point of bonding I would re bond if under 23 k
 

rich.250

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When rich posted that he disconnected the Main earth when doing the 23Kohm test I asked why and understand why he did, but on thinking this over not sure if perhaps it is the right course.

We disconnect the main earth conductor for a Ze in order to prove an external earth path without parallel paths, but like a measured Zs I think that measuring a piece of metal work to prove it's an extraneous conductive part should be done with these paths in place. Because in my mind to prove this metal is an ECP should be done when the installation is "As-Is" not "How-Should" be.

I've argued this before, on here and off, when told a Zs should be calculated and not measured because of parallel paths, but my answer always is, You only get an electrical fault when an installation/circuit is LIVE, and I therefore when it is in use. So I want to know the condition and therefore the value of the Zs when the installation is in use. When a fault happens, the installation/circuit don't say hold on a second lads I need to disconnect all these parallel paths and make sure I can trip the OPD without them.

Yes I agree that perhaps 2 years down the line something can change within the installation, say removing a metallic service to a non metallic one, and those paths are removed, but I have never advocated designing an installation/circuit to rely on parallel paths, but it should be designed to trip the OPD without the paths. In my view these paths are literally a bonus.

So therefore the same with an ECP, I personally think by removing the main earth and those parallel paths your giving the installation a "false" state. The reason we do bond is to bring all these metallic services into the zone at the same potential. by removing your major source of earth aren't you removing your main reference point?
I see what your satin malc, totally.
But isn't the point to see if it's extraneous.....?? Personally If I can't find the point of bonding I'd attach new.
But you could get a reading sufficiently low enough to make you think it is bonded!
Although now thinking about my own method, if I'm going to bond below 23k anyway I may aswell test with the ME in place...
 
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