Current Earth Bonding Regulations

[westie101]

From our document

The PME earthing terminal shall not be made available to the customer unless:
11.3.1 A main equipotential bond of not less than the copper equivalent area shown in Table 2 is installed to bond the incoming metallic gas and water services to the customers’ protective conductors; and
11.3.2 Other exposed metalwork in the premises which is directly connected to or in contact with metalwork buried in the ground is also bonded to the PME earth terminal using conductors of size as detailed in Table 2. Note that such bonds are also main equipotential bonds; and that telecommunication cables are exempt from the requirements of this paragraph 11.3.2

In reference to metallic services we take that clearly to apply to the metallic internal pipework as the services in the street/garden have been plastic for many years

and this, which possible answers a question elsewhere

Electricity North West shall not connect or permit the connection of a PME earthing terminal to the customer’s protective conductors, unless satisfied as far as reasonably practicable that the necessary bonding has been made. A contractor’s certificate will normally be required for this purpose.

Generally as far as we are concerned no bonding, no connection

 

[ban-all-sheds]

In reference to metallic services we take that clearly to apply to the metallic internal pipework as the services in the street/garden have been plastic for many years

Then how does the metallic internal pipework introduce a potential into the equipotential zone of the house?

Electricity North West shall not connect or permit the connection of a PME earthing terminal to the customer’s protective conductors, unless satisfied as far as reasonably practicable that the necessary bonding has been made. A contractor’s certificate will normally be required for this purpose.

Intrinsic to the presence of bonding are extraneous-conductive-parts which require them. If there are no e-c-ps then there is no need for bonding, on account of there being nothing to bond.

So that rule is perfectly fine.

Generally as far as we are concerned no bonding, no connection

But is that rule corrupted in practice to "no bonding, no connection, even if no bonding is required"?

 

[JohnW2]

It could be a plastic joint with the resistance of the water being measured.

Perhaps - although I would seriously doubt that one would measure resistances (particularly at low voltage) as low as we are talking about by that mechanism. In any event ...

Easier to bond the 'offending' pipe than hunt for the cause.

Exactly my point! Despite what you suggested, I would not be happy to regard a pipe as 'effectively connected to MPB' if the measured resistance was any where near 1666Ω. Frankly, I would probably be a bit concerned with 16Ω!

However, I wonder exactly what you are suggesting, and where you would bond it to, and what with? Are you talking about using a G/Y cable to establish an 'effective connection to the MEB' for the purpose of satisfying 701.415.2(vi) and thereby (assuming the other requirements were satisfied) allowing you to omit supplementary bonding within the bathroom - or are you talking about supplementary bonding everything within the bathroom?

Kind Regards, John

 

[JohnW2]

From our document...

The PME earthing terminal shall not be made available to the customer unless:
11.3.1 A main equipotential bond of not less than the copper equivalent area shown in Table 2 is installed to bond the incoming metallic gas and water services to the customers’ protective conductors; and ...

In reference to metallic services we take that clearly to apply to the metallic internal pipework as the services in the street/garden have been plastic for many years

The regulation is essentially fine, but, with respect, the interpretation you are suggesting makes absolutely no sense. Do 'you' (DNOs) do not see the word "incoming" in that regulation?

As I said before, to require metal pipework within a building to be main bonded when the only connection to the outside world is plastic is not only (electrically) crazy in itself, but there's no obvious reason why the same crazy requirement would not then apply to every other metal object within the building. What is the difference between a copper pipe which is electrically insulated from the outside world and, say, a metal handrail on a staircase?

You are often (very reasonably) critical of those who are obsessed with doing things 'per a book' (usually BS76761), despite electrical common sense - but how do you apply that laudable view to the above?

Kind Regards, John

 

[ban-all-sheds]

So, any parts which are between 1,666 and 23,000Ω should still be bonded.

23kΩ?

 

[EFLImpudence]

So, any parts which are between 1,666 and 23,000Ω should still be bonded.

23kΩ?

Yes, what is your point?

 

[JohnW2]

So, any parts which are between 1,666 and 23,000Ω should still be bonded.

23kΩ?

AIUI, 23kΩ (i.e 10mA at 230V) is the figure that EFLI always quotes as the resistance to earth above which something can be considered as 'not liable to introduce earth potential' and hence not an extraneous-c-p (hence not needing bonding). There is clearly some resistance (to earth) above which that becomes a reasonable assumption, but I'm not sure where EFLI's 23kΩ figure comes from - presumably some guidance document. I'm sure he will tell us!

In practice, of course, most conductors which are not extraneous-c-ps will have a 'near-infinite' resistance to earth - so these arbitrary thresholds will rarely be of any importance.

Kind Regards, John

 

[EFLImpudence]

However, I wonder exactly what you are suggesting, and where you would bond it to, and what with? Are you talking about using a G/Y cable to establish an 'effective connection to the MEB' for the purpose of satisfying 701.415.2(vi) and thereby (assuming the other requirements were satisfied) allowing you to omit supplementary bonding within the bathroom - or are you talking about supplementary bonding everything within the bathroom?

To omit supplementary bonding all (now) four conditions must be met.

We are dealing with one pipe which is not effectively connected to the MEB - by definition >1,666Ω.

Therefore I would think it sufficient to just connect the 'offending' pipe to another which is effectively connected.

 

[EFLImpudence]

AIUI, 23kΩ (i.e 10mA at 230V) is the figure that EFLI always quotes as the resistance to earth above which something can be considered as 'not liable to introduce earth potential' and hence not an extraneous-c-p (hence not needing bonding). There is clearly some resistance (to earth) above which that becomes a reasonable assumption, but I'm not sure where EFLI's 23kΩ figure comes from - presumably some guidance document. I'm sure he will tell us!

It is in GN8 and other documents dealing with the body and electricity and it (10mA) is the accepted figure below which a person can let go.
It is up to the designer to use whichever figure is considered safest - 10mA, 5mA, whatever.

The resulting limits are, as has been said, nominal figures.

In practice, of course, most conductors which are not extraneous-c-ps will have a 'near-infinite' resistance to earth - so these arbitrary thresholds will rarely be of any importance.

As above, the fact that they may rarely be of importance does not alter the result of the calculation.
I don't know how else you expect the rules to be written without the use of nominal values.

 

[JohnW2]

However, I wonder exactly what you are suggesting, and where you would bond it to, and what with? Are you talking about using a G/Y cable to establish an 'effective connection to the MEB' for the purpose of satisfying 701.415.2(vi) and thereby (assuming the other requirements were satisfied) allowing you to omit supplementary bonding within the bathroom - or are you talking about supplementary bonding everything within the bathroom?

To omit supplementary bonding all (now) four conditions must be met.

Indeed.

We are dealing with one pipe which is not effectively connected to the MEB - by definition >1,666Ω.

Indeed - well, greater than something, whether that be 1666Ω, 16Ω or whatever one decides to use (701.415.2(vi) itself obviously does not define 'effectively connected').

Therefore I would think it sufficient to just connect the 'offending' pipe to another which is effectively connected.

Possibly/probably (at least,in common sense terms), but I would be interested to know what you would call that 'connection' you installed! However, in practice, I would suspect that it would be pretty likely that if one of the pipes in the bathroom had less than an 'effective connection' to the MPB, then so probably would all the other pipes there, so what would you do then - just supplementary bond everything?

Kind Regards, John

 

[EFLImpudence]

We are dealing with one pipe which is not effectively connected to the MEB - by definition >1,666Ω.

Indeed - well, greater than something, whether that be 1666Ω, 16Ω or whatever one decides to use (701.415.2(vi) itself obviously does not define 'effectively connected').

Yes it does.
The note below refers to 415.2.2 which states <50/Ia is the determining value.
The same as supplementary bonding is not required (rather than may be omitted) if the values are <50/Ia of the OPD.

Therefore I would think it sufficient to just connect the 'offending' pipe to another which is effectively connected.

Possibly/probably (at least,in common sense terms), but I would be interested to know what you would call that 'connection' you installed!

It is obviously supplementary bonding, an item of which that may not be omitted.

However, in practice, I would suspect that it would be pretty likely that if one of the pipes in the bathroom had less than an 'effective connection' to the MPB, then so probably would all the other pipes there,

I don't see why that would be the case.
It could be the one plastic pipe connection.

so what would you do then - just supplementary bond everything?

Well, obviously if the conditions for omitting supplementary bonding are not met then the supplementary bonding may not be omitted therefore it shall be fitted.

 

[JohnW2]

It is in GN8 and other documents dealing with the body and electricity and it (10mA) is the accepted figure below which a person can let go. It is up to the designer to use whichever figure is considered safest - 10mA, 5mA, whatever.

Yes, I understand what 23k represents in physiological terms. What I am wondering/questioning is who/what has decided (and stated) that it is an acceptable criterion for decided whether or not something is an extraneous-c-p. (in many senses, I personally agree that it sounds like a 'reasonable' criterion).

As above, the fact that they may rarely be of importance does not alter the result of the calculation. I don't know how else you expect the rules to be written without the use of nominal values.

I agree with your first sentence there. As regards the second sentence, I suppose my point is that 'the rules' (regulations) do not provide any nominal value for considering something as an extraneous-c-p (merely talking in terms of not being 'liable to introduce a potential' - which is obviously strictly true regardless of the resistance to earth). You are assuming, on the basis of a guidance document, that it is acceptable to utilise a criterion relating to the physiological effects of a current that could flow through a human being via that conductor - but, AFAIAA, nowhere do the regs actually indicate that as an acceptable way of defining an extraneous-c-p ... or have I missed something?

Kind Regards, John

 

[JohnW2]

... (701.415.2(vi) itself obviously does not define 'effectively connected').

Yes it does. The note below refers to 415.2.2 which states >50/Ia is the determining value.

Ah, yes, I missed that. However, as we've discussed before, strictly speaking 415.2.2 is about the assessment of the adequacy of supplementary bonding, not for deciding whether supplementary bonding is required. I suppose that the footnote of 701.415.2 may 'over-ride' that!

The same as supplementary bonding is not required (rather than may be omitted) if the values are >50/Ia of the OPD.

I presume you mean <50/Ia.

Therefore I would think it sufficient to just connect the 'offending' pipe to another which is effectively connected.

Possibly/probably (at least,in common sense terms), but I would be interested to know what you would call that 'connection' you installed!

It is obviously supplementary bonding, an item of which that may not be omitted.

I asked because you only spoke of connecting it to another pipe. Would you also connect it to a CPC - since, as I understand it, without such a connection it would not qualify as 'supplementary bonding'. BS7671 does not seem to have a word for "plumbers' cross-bonding" (joining pipes with G/Y without connecting to a CPC).

Kind Regards, John

 

[EFLImpudence]

Yes, I understand what 23k represents in physiological terms. What I am wondering/questioning is who/what has decided (and stated) that it is an acceptable criterion for decided whether or not something is an extraneous-c-p. (in many senses, I personally agree that it sounds like a 'reasonable' criterion).

I am all for the thirst for knowledge and playing Devil's advocate but it does seem to be stretching things somewhat to question why and who decided something with which you agree and may have decided yourself had you been in the position.

I agree with your first sentence there. As regards the second sentence, I suppose my point is that 'the rules' (regulations) do not provide any nominal value for considering something as an extraneous-c-p (merely talking in terms of not being 'liable to introduce a potential' - which is obviously strictly true regardless of the resistance to earth). You are assuming, on the basis of a guidance document, that it is acceptable to utilise a criterion relating to the physiological effects of a current that could flow through a human being via that conductor - but, AFAIAA, nowhere do the regs actually indicate that as an acceptable way of defining an extraneous-c-p

So we have to look elsewhere.

... or have I missed something?

I doubt it.

 

[EFLImpudence]

Yes, of course < thanks.