Main water and gas bonding question

[electrospark]

Hi, quick question.

I have an installation where the water and gas are not bonded within the flat but is bonded externally to the flat in the common parts where they enter the installation from the road.
I have spoken with the NICEIC who advise me that this is ok and that the individual flats do not to be bonded.
My question is, what is saying that the pipes have been connected/repaired out of sight in the common parts with plastic and that there is no continuity.
I should do an R2 reading to ensure the pipe work is continuous to the flat but should this be within certain tolerances?

Thanks

 

[flyingsparks]

IIRC the continuity of a bond should be less than 0.1 ohms.
In theory the installation is bonded at the origin as required. There's no difference really as in a house it may be bonded at the origin then plastic fittings used to break to continuity of the pipe work.

 

[JohnW2]

I have an installation where the water and gas are not bonded within the flat but is bonded externally to the flat in the common parts where they enter the installation from the road. ... I have spoken with the NICEIC who advise me that this is ok and that the individual flats do not to be bonded.

Fair enough - that sounds reasonable.

My question is, what is saying that the pipes have been connected/repaired out of sight in the common parts with plastic and that there is no continuity.

This really only applies to the water pipes, since plastic gas pipes are not allowed within domestic premises. If there were a plastic interruption in the pipework between where it enters the building and the flat, then there would surely be even less reason why it would need bonding in the flat, wouldn't there? (i.e. with a plastic interruption, it would not be an extraneous-conductive-part as far as the flat was concerned, and hence would not require main bonding).

I should do an R2 reading to ensure the pipe work is continuous to the flat but should this be within certain tolerances?

Given that we're not talking about a cable, I'm not quite sure what you mean by an R2 reading - do you mean testing the continuity of the pipework? If so, see above - if there were no continuity between pipework entering the building and pipework entering the flat, there would presumably be no need for main bonding within the flat.

Kind Regards, John

 

[JohnW2]

IIRC the continuity of a bond should be less than 0.1 ohms.

There is a guideline somewhere (OSG? GN3?) that main bonding conductors should be a maximum of 0.05Ω, but the OP seemed to be talking about the resistance/continuity of the pipework, not of a bonding conductor.

Kind Regards, John

 

[Spark123]

I believe the 0.05Ω is derived from the current needed to blow a 100A BS1361 fuse within 5 seconds.
Basically it just depends on whether or not you treat each flat as it's own equipotential zone or the building as a whole as a single eq. zone.

 

[EFLImpudence]

Hi, quick question.

Probably not a quick answer.

I have an installation where the water and gas are not bonded within the flat but is bonded externally to the flat in the common parts where they enter the installation from the road.

As far as the regulations are concerned it depends on your definition of premises and installation and origin.
Is each flat a separate premises and is each a separate installation with a separate origin?

I have spoken with the NICEIC who advise me that this is ok and that the individual flats do not to be bonded.

I would give that no credence.

My question is, what is saying that the pipes have been connected/repaired out of sight in the common parts with plastic and that there is no continuity.

As has been said that would remove any earth potential but then it may be possible to introduce other potential of which you would be unaware.
The problem is the removal of the bond which is unknown to you.

I would, as is illustrated in GN8, separately bond each flat to make each an equipotential zone.

I should do an R2 reading to ensure the pipe work is continuous to the flat but should this be within certain tolerances?

If you mean test between the pipe in your flat and the MET in your flat then the result may be satisfactory at the time but not tomorrow should someone do something undesired.

IIRC the continuity of a bond should be less than 0.1 ohms.

The figure is 0.05Ω but is merely an accepted value of negligible impedance between the conductor and the pipe.
It has nothing to do with the impedance of the conductor between the MET and the pipe.

In theory the installation is bonded at the origin as required. There's no difference really as in a house it may be bonded at the origin

Except that in A house you can see if it is still there...

then plastic fittings used to break to continuity of the pipe work.

... and no potential can be introduced from elsewhere.

I believe the 0.05Ω is derived from the current needed to blow a 100A BS1361 fuse within 5 seconds.

That would result in 4,600A; considerably more than the 630A required for a BS1361 and also more than the 1,800A for 0.1s.

Basically it just depends on whether or not you treat each flat as it's own equipotential zone or the building as a whole as a single eq. zone.

Agreed and I would.

 

[JohnW2]

I believe the 0.05Ω is derived from the current needed to blow a 100A BS1361 fuse within 5 seconds.

That sounds credible - although that obviously must involve assumptions about the impedance of other parts of the current path.

Basically it just depends on whether or not you treat each flat as it's own equipotential zone or the building as a whole as a single eq. zone.

I would have said that, by definition, any sub-part of an equipotential zone must also be an equipotential zone (otherwise the whole zone wouldn't have been equipotential) - so if the whole building is an equipotential zone, then so must be each flat.

Kind Regards, John

 

[Spark123]

Maybe it is to blow it within 5s if a 50v> touch voltage occurs on a PEB, someone will remember!

 

[JohnW2]

I believe the 0.05Ω is derived from the current needed to blow a 100A BS1361 fuse within 5 seconds.

That would result in 4,600A; considerably more than the 630A required for a BS1361 and also more than the 1,800A for 0.1s.

Indeed. As I've just written, if Spark123's theory is right, the figure obvioulsy must involve assumptions about the impedance of other parts of the likely current path.

Basically it just depends on whether or not you treat each flat as it's own equipotential zone or the building as a whole as a single eq. zone.

Agreed and I would.

That sounds reasonable but, as I've just written, if the whole building is an equipotential zone, then it's theoretically impossible for any sub-part of the building (e.g. a flat) to not also be an equipotential zone. If everything within the whole building is considered to be 'equipotential', then so must everything within any sub-part of that building.

Kind Regards, John

 

[Lectrician]

Hi, quick question.

I have an installation where the water and gas are not bonded within the flat but is bonded externally to the flat in the common parts where they enter the installation from the road.
I have spoken with the NICEIC who advise me that this is ok and that the individual flats do not to be bonded.
My question is, what is saying that the pipes have been connected/repaired out of sight in the common parts with plastic and that there is no continuity.
I should do an R2 reading to ensure the pipe work is continuous to the flat but should this be within certain tolerances?

Thanks

If it's repaired in plastic in the common area (and I hope you don't mean gas!), then is the part in the flat then classed as extraneous?

Surprised at the the NIC reply, given their literature on flats, clearly showing a separate bond in the flat to the flats CU, and a bond at building entry back to the BEMP, building Earth marshalling point. Granted, the literature is a few years old now.

 

[JohnW2]

Maybe it is to blow it within 5s if a 50v> touch voltage occurs on a PEB, someone will remember!

On reflection, I'm not so sure about this talk of 100A fuses blowing. AIUI, the main hypothesised situation in which high currents might flow through a main bonding conductor is when a supply-side neutral fault results in a TN-C-S 'earth' rising considerably in potential (above true earth). However, that current will then be shared between the L supplies (hence cutout fuses) of several. perhaps many, installations - so the current going through each fuse may not be all that high.

Kind Regards, John

 

[JohnW2]

Surprised at the the NIC reply, given their literature on flats, clearly showing a separate bond in the flat to the flats CU ...

The advantage of that is, I suppose, that each flat then definitely becomes an equipotential zone, regardless of what may happen to the ('primary') main bonding of the building as a whole (over which the owner or occupier of a flat may have no control).

As I've said, if the whole building is an equipotential zone, then so must be each sub-unit (e.g. flat) within it - but that is only true so long as the building as a whole does remain an equipotential zone (i.e. so long as no-one interferes with the bonding of extraneous-c-ps where they enter the building).

Kind Regards, John

 

[deadshort]

If i was rewiring a subdivided property i would bond the gas and water as i would a detached house i.e., at the point of entry to the flat to my new CU. If there were any issues in the future you have bonded the installation and covered your bottom !

If the water supply is replaced with plastic out with your installation -not your problem as you have bonded the your flat and pipe work within.

Kind regards,

DS

 

[JohnW2]

If i was rewiring a subdivided property i would bond the gas and water as i would a detached house i.e., at the point of entry to the flat to my new CU. If there were any issues in the future you have bonded the installation and covered your bottom !

Indeed, as I recently wrote, it ensures that one is not depending upon anything happening outside of the boundaries of the flat.

If the water supply is replaced with plastic out with your installation -not your problem as you have bonded the your flat and pipe work within.

Only a problem for you if you were one of those people who believes that to unnecessarily bond something which is not an extraneous-c-p (which is what the pipe entering the flat would then be) is undesirable, since it can theoretically increase hazards.

Kind Regards, John

 

[EFLImpudence]

If the water supply is replaced with plastic out with your installation -not your problem as you have bonded the your flat and pipe work within.

Only a problem for you if you were one of those people who believes that to unnecessarily bond something which is not an extraneous-c-p (which is what the pipe entering the flat would then be) is undesirable, since it can theoretically increase hazards.

As has been said that would remove any earth potential but then it may be possible to introduce other potential of which you would be unaware.

I would, as is illustrated in GN8, separately bond each flat to make each an equipotential zone.