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Topic Title: PME, no bonding, and no RCD
Topic Summary: C1 or C2?
Created On: 06 October 2018 07:59 PM
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 06 October 2018 07:59 PM
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chrispearson

Posts: 530
Joined: 15 February 2018

Well, admittedly there is a 100 mA S type which serves some of the circuits, but no bonding of any type.

I think C2, but a DNO would be within its rights not to connect.

Opinions on a postcard please.
 06 October 2018 08:18 PM
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geoffsd

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Is bonding required? Are they extraneous-conductive-parts? If they are, then C2; if not, then it's alright.

If 30mA RCDs would be required now, I consider that as improvement recommended, so C3.
Others disagree and think it 'potentially dangerous', so C2.

It's up to you..


How would the DNO know?
 06 October 2018 08:56 PM
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Zoomup

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Exactly. I inspected a building today used as a holiday let. The water supply had a lovely green and yellow main bonding cable attached to the copper pipe, but the incoming water pipe was plastic when I looked further. No gas at all.

Z.
 06 October 2018 09:30 PM
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UKPN

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The bonding requirements if a PME terminal is utilised are the same irrespective of whether there is an insulated insert or copper /steel piping. That is, a green/yellow conductor at the point of entry or near to if not practical, with a minimum of 10mmsq in most cases, some 16mmsq.

Regards, UKPN
 06 October 2018 09:47 PM
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Zoomup

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Originally posted by: UKPN

The bonding requirements if a PME terminal is utilised are the same irrespective of whether there is an insulated insert or copper /steel piping. That is, a green/yellow conductor at the point of entry or near to if not practical, with a minimum of 10mmsq in most cases, some 16mmsq.



Regards, UKPN


And if the main incoming water pipe is plastic and all internal metal pipes are not extraneous conductive parts?

Z.
 07 October 2018 12:15 PM
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davezawadi

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It appears that UKPN is somewhat out of date. Installations to BS7671 are deemed to comply with the ESQCR requirements.
Bonding requirements are very clear in BS7671, and as we endlessly say:
Main protective bonding is required if extraneous conductive parts could introduce an external potential into the equipotential zone. Clearly there is no danger if they cannot and so Main Protective Bonding is not required. 411.3.1.2 in the BBB.

Extraneous conductive parts inside the equipotential zone never require bonding, as they cannot, by definition, gain a potential which could be dangerous.
Pipework connected to an electrical supply (Immersion heaters, boilers etc) already must have a CPC connection, and therefore are Protective Bonded to the MET, by the CPC. Further bonding is only required if it is decided that there is some kind of additional risk, then Supplementary Protective Bonding may be installed. The wonderful "Cross Bonding" of plumbers to their pipes is not required! For bathrooms etc see 701.415.2. When all circuits in the bathroom are RCD protected at 30mA and 200ms (standard RCD) then protective equipotential bonding is not required.

Not too difficult, and now the codes: (assuming accessible appliance / accessory in the room)
No CPC - C1
No RCD and no bonding - C2
RCD and no bonding - nothing
Full bonding and No RCD - nothing
Non-compliance with Zones - C2
I cannot think of a C3 situation in except cables outside of safe zones.

I am beginning to think that much more training is required somewhere,

-------------------------
David
BSc CEng MIET
david@ZawadiSoundAndLighting.co.uk
 07 October 2018 12:58 PM
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geoffsd

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Originally posted by: davezawadi

Extraneous conductive parts inside the equipotential zone never require bonding, as they cannot, by definition, gain a potential which could be dangerous.

Has something been lost in translation?

Pipework connected to an electrical supply (Immersion heaters, boilers etc) already must have a CPC connection, and therefore are Protective Bonded to the MET, by the CPC. Further bonding is only required if it is decided that there is some kind of additional risk,

Well, with PME that bonding must be 10sq.mm. minimum so it is unlikely that a CPC will be adequate.
Plus the requirement that the MPB be connected as near as practicable to the point of entry to the premises is presumably to avoid alterations within the premises removing that connection.

For bathrooms etc see 701.415.2. When all circuits in the bathroom are RCD protected at 30mA and 200ms (standard RCD) then protective equipotential bonding is not required.

There are other requirements which must be met before supplementary bonding may be omitted.

Not too difficult,

Nevertheless.




and now the codes: (assuming accessible appliance / accessory in the room)

No CPC - C1
No RCD and no bonding - C2
RCD and no bonding - nothing
Full bonding and No RCD - nothing
Non-compliance with Zones - C2

I cannot think of a C3 situation in except cables outside of safe zones.
I am beginning to think that much more training is required somewhere,

The OP and thread are not related to bathrooms but the whole installation.
 07 October 2018 07:01 PM
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chrispearson

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Thank you for the comments so far.

Perhaps I should have made it clearer that the water supply is metallic. Not a trace of bonding in sight!

I think C2, but I wondered whether anybody would argue for C1.

David, if no CPC = C1, why not C1 for absence of MPBC?
 07 October 2018 10:25 PM
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mapj1

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No CPC to the building means you have single fault to danger for any one defective appliance can liven up all the metal in the house, and nothing will trip. In effect there is no ADS.

No bonding means that as you do have a CPC all your ADS still works just fine, but the far less likely case of an external network fault that introduces an offset between the CPC and the true ground, but an external fault is likely to be cleared quite quickly.

-------------------------
regards Mike
 08 October 2018 09:45 AM
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chrispearson

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Originally posted by: mapj1

No CPC to the building means you have single fault to danger for any one defective appliance can liven up all the metal in the house, and nothing will trip. In effect there is no ADS.

No bonding means that as you do have a CPC all your ADS still works just fine, but the far less likely case of an external network fault that introduces an offset between the CPC and the true ground, but an external fault is likely to be cleared quite quickly.


Mike, thank you for the clear explanation, which makes good sense to me. C2 it is then.
 08 October 2018 10:18 AM
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davezawadi

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Well Geoff, yes my mistake on the exact definition, as you say extraneous conductive parts are only those liable to introduce a potential. However you undoubtedly understood what I was trying to say (whilst in a bit of a hurry) which was that all other metallic conductive parts which are present inside the equipotential zone do not require bonding, and only appliances require earthing.

So to be clear extraneous conductive parts are only those which are able to introduce an external potential. Other conductive items inside the equipotential zone do not have a special name, including plumbing, they are considered benign.

The main point of my post was to establish that random bits of plumbing etc. do not need to be bonded, as stated in the OP, and that this section had subtly changed with the addition of electrically insulating inserts to incoming metal services.

Those still confused about bathrooms etc. may care to refer to section 701.

-------------------------
David
BSc CEng MIET
david@ZawadiSoundAndLighting.co.uk
 08 October 2018 04:41 PM
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Zoomup

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Hello David,
I seem to remember a recent discussion on the subject of bonding, and I think that we concluded that even internal conductive pipes such as those copper pipes buried in a ground floor, could be considered as extraneous conductive parts if "earthy," even if they are internal to the building, perhaps buried in a damp ground floor as opposed to being laid in a dry floor above a damp proof membrane. Or even if they are run in intimate contact with an old damp wall downstairs they may be included. I don't think that all extraneous conductive parts have to actually physically come in from outside a building, just introduce a potential into it.

Z.
 08 October 2018 05:43 PM
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geoffsd

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Yes.

It depends what you class as "outside the building" - in the ground below the floor is classed as outside the building as far as e-c-ps are concerned.
 09 October 2018 11:00 AM
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davezawadi

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Yes that is perfectly true, as is something being able to introduce a potential due to a fault condition in another part of a building (probably not domestic, due to distances). Pipes are not usually fitted in the "wet" side of concrete foundations or floors, because they tend to corrode, and leak (surprisingly common in heating pipes between buildings), and repair is very difficult.

As to Chris's question, why not a C1 for no MPB if it is required? This in my view is C2 because it is not immediately dangerous, but potentially could be given a fault condition elsewhere. It is nothing like an exposed live conductor, and I think that we should keep the C1 for the really bad ones, not sprinkle them all over the sheet, as some do. For example I have seen C1s given to lack of RCD sockets which could be used outside. This is a bit excessive because most (if not all) garden maintenance appliances are class 2, and even if class 1 a fault is required to present danger. Sometimes the excuse "I am covering myself" is given, but really this only shows a lack of confidence in your opinion. It is only a paperwork change, so why was it previously not a problem? It probably increases safety slightly, but many more accidents are caused by incompetent use of garden tools, perhaps they should all be banned too?

-------------------------
David
BSc CEng MIET
david@ZawadiSoundAndLighting.co.uk
 09 October 2018 01:31 PM
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chrispearson

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David, thank you. My thinking was that there seems to be a contradiction between C2 on the one hand, and the fact that some DNOs state that they will connect up a PME supply only when they are satisfied that adequate bonding is in place on the other hand.
 09 October 2018 10:41 PM
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UKPN

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"It appears UKPN is out of date"
Ok, For PME posters should get away from BS7671. (as it is correctly called). The "wiring regulations" is the out of date title. ESQCR is the legal requirement and as everybody actually in the industry knows BS7671 is a code of practice. The bonding requirements of PME are different to those of BS7671 Requirements for electrical installations (as it is correctly known). If a contractor comes across an installation utilising a PME terminal (as in this case) with no bonding he/she should notify the customer that as a matter of urgency the bonding is fitted as per the legal requirements or there is a risk of withdrawal of that facility.
Finally, for my friend with the "out of date comment" and the comment regarding the tie in between ESQCR and BS7671 he may note that for bonding there is the caveat "EXCEPT WHERE PME APPLIES"

Regards UKPN
 10 October 2018 12:31 AM
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mapj1

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While I agree that the ESQCR, in full, here is made under statutory instrument, and DNOs must follow it, while BS7671 is only a standard, and none of us is under obligation to follow it, I can find no part in the ESQCR legislation, that demands customer side bonding. Restrictions on what you can connect a PEN to, yes, and rules for the DNO in sections 7 8and 9 but the consumer does not have a PEN conductor, as by it reaches him, the earth and neutral have been separated.
Another possible clause you may be thinking of, is 25, which allows a DNO to refuse connection to any installation which "fails to comply with British Standard Requirements or these Regulations;" which are explained as meaning the requirements of BS7671 in the intro. So in effect when BS7671 changes what is or is not acceptable then what is acceptable grounds not to connect also changes in that section of the ESQCR, the two are in lockstep.

-------------------------
regards Mike
 10 October 2018 01:04 AM
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geoffsd

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Originally posted by: UKPN

Ok, For PME posters should get away from BS7671. (as it is correctly called). The "wiring regulations" is the out of date title.

It still says "IET Wiring Regulations"on mine as well as "Requirements for Ellectrical Installations".

If a contractor comes across an installation utilising a PME terminal (as in this case) with no bonding he/she should notify the customer that as a matter of urgency the bonding is fitted as per the legal requirements or there is a risk of withdrawal of that facility.

What if there are no extraneous-conductive-parts?
What are these legal requirements?

Finally, for my friend with the "out of date comment" and the comment regarding the tie in between ESQCR and BS7671 he may note that for bonding there is the caveat "EXCEPT WHERE PME APPLIES"

There is another sentence for WHERE PME APPLIES which merely relates to the csa of a bonding conductor. It certainly does not state that bonding shall be applied differently than other earthing methods or where none is required.

544.1.2 has, for years, been incorrect in its instruction. This has, in the latest edition, been rectified.
 10 October 2018 09:11 AM
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Zoomup

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544.1.2 has, for years, been incorrect in its instruction. This has, in the latest edition, been rectified.


Indeed, the 18th edition now uses the words: "The main protective bonding connection to any extraneous-conductive parts such as gas, water or other metallic pipework or service........". The 17th edition did not include the words "extraneous conductive parts."

Z.
 10 October 2018 11:47 AM
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geoffsd

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Yes, that - and the instruction that the actual extraneous-c-p be left unbonded.
IET » Wiring and the regulations » PME, no bonding, and no RCD

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