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Topic Title: EICR advice
Topic Summary: Code for earth bonding arrangements.
Created On: 06 August 2014 03:00 PM
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 06 August 2014 03:00 PM
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NRG32

Posts: 9
Joined: 27 November 2013

Good afternoon, I would like to ask the friendly engineers in IET cyber space a question.

I haven't done a PIR in a good number of years. Now it has changed to EICR and I have agreed to do one for a family member.

The main issue is its a 1970s council property. Now in the 70s I was in shorts and dreaming of being an astronaut or jockey! So I cant say for sure if back then it was standard to have no earth bonding to incoming services, i.e. water and gas. Is this correct?

So we have missing main bonding conductors. This I would normally upgrade but in this case it would mean huge disruption and hundreds of pounds of repair work.

I have noted that someone has made an effort to upgrade by installing 6mm from local sockets to the services i.e. water and gas. Which I see no problem with and there has also been a CU upgrade with a 30mA RCD. So clearly the installation has been improved.

Now what code do I enter in the EICR?
I don't see any danger and an improvement is out of the question as far a the owner is concerned due to cost.

Any feed back appreciated.
 06 August 2014 03:54 PM
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AJJewsbury

Posts: 11467
Joined: 13 August 2003

The main issue is its a 1970s council property. Now in the 70s I was in shorts and dreaming of being an astronaut or jockey! So I cant say for sure if back then it was standard to have no earth bonding to incoming services, i.e. water and gas. Is this correct?

In a way it's a mute question, as a periodic inspection is always done with reference to the current regs, not past ones. (Although main bonding has been a requirement for as long a I can remember)

I have noted that someone has made an effort to upgrade by installing 6mm from local sockets to the services i.e. water and gas.

A bit dodgy that - you've now got the socket circuit c.p.c. (i.e. two or perhaps a single 1.5mm2 or even 1.0mm2) being called upon to act as a main bonding conductor. For a PME supply (which most public networks now are, regardless of how things appear at the cutout) that means it could be carrying diverted N currents - for which anything under 10mm2 doesn't comply and below 6mm2 the DNOs will usually refuse a connection to. It may be that the shock risk has been reduced somewhat, but perhaps the fire risk has been increased significantly in return. (Although the same risk would apply if any class 1 equipment was in contact with exposed-conductive-parts - immersion heaters, boilers and so on).

Now what code do I enter in the EICR?

Are the pipes really extraneous-conductive-parts? Most underground water and gas pipes have been replaced by plastic so probably aren't liable to introduce an earth potential any more, in which case bonding wouldn't be required anyway. What's the earthing system? If its really is TN-S (e.g. single electrode PNB) then the risks are probably minimal, for TT the missing bonding will mean far higher touch voltages within the installation, for PME (TN-C-S) there's no protection from shock in the case of supply network N faults and fire risks from diverted network N currents in normal circumstances. So a lot to take into account.

- Andy.
 06 August 2014 04:42 PM
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mapj1

Posts: 2806
Joined: 22 July 2004

There are guidance notes, some of which I don't believe are always realistic in every case here see the appendix for example codes.
These give some ideas as to how seriously different sorts of things are taken, and if like me you sometimes disagree, at least you know what you are changing!

They reckon missing bonds is 'potentially dangerous' whatever that means in practice.

While main bonding might have been absent in 1950 ish, by the 1966 edition and onwards it really should have been present, though maybe at an imperial size similar to 4mm or 6mm.
Might be worth unshipping the stuff you can see, and testing with a meter - there may be hidden bonding under the floor for example..

-------------------------
regards Mike
 06 August 2014 05:02 PM
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perspicacious

Posts: 7235
Joined: 18 April 2006

"Now what code do I enter in the EICR?
I don't see any danger and an improvement is out of the question as far a the owner is concerned due to cost."


Should the cost of remedial work affect your technical decision making in accepting the risk transfer of an EICR?

Regards

BOD
 06 August 2014 05:45 PM
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NRG32

Posts: 9
Joined: 27 November 2013

Thanks for the replies.
AJ; Its PME. Definitely extraneous pipes. I am not sure I follow you on the increased fire risk. Are you saying fault currents could make their way from the public supply into the property and frazzle the ring cpc. Is this likely? Please explain.

mapJ; I am trying to get to the bottom of this as to why there was no original bonding. I will do some tests to see if there is any hidden bonding but since there are no conductors going back to the CU or suppliers earth I doubt it.
However I just had a thought. There was what looked like a 4mm earth darting down a telecoms conduit which I assume is for the telecoms but will investigate.

pesrp; you are quite right that safety should come first but I am afraid cost does have its limitations. I am trying to see if there are any clever ways of introducing new bonding cables but I am not a magician. And to think the property has been here for 40 years probably half that time under council management and it seems that its never been a cause for concern. And as my dear mother would point out that there was nothing wrong with it before!
 06 August 2014 05:48 PM
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UKPN

Posts: 513
Joined: 17 January 2012

"fire risk from diverted neutral currents in normal??? operation"

has our poster read the topic?

ie=1970 building=hello! 44 years old!!!

Regards.
 06 August 2014 06:35 PM
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aligarjon

Posts: 2837
Joined: 09 September 2005

In answer to your question lack of main bonding will be a C2, which basically is an unsatisfactory report. What makes it so disruptive. Is outside and round the outside possible.

Gary

-------------------------
Specialised Subject. The Bleedin Obvious. John Cleese
 06 August 2014 06:47 PM
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bobzzz

Posts: 49
Joined: 13 May 2014

Seeing as the CU was replaced the following might be relevant. Unfortunately the regs does not really take economical things into consideration

Main earthing and bonding

The installation of a replacement consumer unit
must comply with the current edition of
BS 7671. In particular, the installer must, as a
minimum, verify that:
a) the main earthing terminal of the
installation is connected to an adequate
means of earthing via a suitably sized
earthing conductor
b) the main protective bonding is adequate,
and
c) the meter tails and the distributor's
equipment have adequate current-carrying
capacity.
Note. Some electricity distributors have
requirements regarding the earthing conductor,
main bonding conductors and meter tails that
exceed the requirements of BS 7671.
If any of the above conditions (a), (b) or (c) is
not met, the customer should be informed that
upgrading is required.


source

Also a very useful piece on classification codes here

-------------------------
Want to know how to become an electrician? Follow the link electriciancentre.co.uk/electrician-courses/
 06 August 2014 06:52 PM
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jcm256

Posts: 1868
Joined: 01 April 2006

It may have been TT at one time before PME came on the scene, in which case a fault voltage operated protective device be fitted. With such a device care had to be taken to avoid installing near metalwork which may become electrically linked to the installation metalwork (such as an immersion heater) therefore shorting out the voltage sensitive element and making it inoperative. Water pipe bonding would be the same.
Bonding to water pipes should have been done at the time PME was made available. Clip earthing conductor around the wall with protection, or dig a trench from the MET if meter board is in a outhouse, to a point near the kitchen sink hole through the wall above damp course to the main stop cock.
 06 August 2014 07:10 PM
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NRG32

Posts: 9
Joined: 27 November 2013

Thanks for the replies.
UKPN; I have no idea what you are trying to say. I have not established the exact year of the building. I know for a fact and from experience that electrical installations suffer over time from shoddy diy work and below standard alterations and additions. In this case the installation is in reasonably good condition just because it is 40 years old does not necessarily ring alarm bells. thanks for guiding me to the topic you mentioned. I could not find it.
aligarjon; thanks for your input. I am planning some potential routes for new cables. May need to get the poly filler out!
bob; I cant really start an investigation and hunt down the installer of the CU, all though they did what looks like a good job. thanks for the link its useful.
 06 August 2014 11:02 PM
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AJJewsbury

Posts: 11467
Joined: 13 August 2003

AJ; Its PME. Definitely extraneous pipes. I am not sure I follow you on the increased fire risk. Are you saying fault currents could make their way from the public supply into the property and frazzle the ring cpc. Is this likely? Please explain.

Not fault currents. It's a feature of the PME system. The supply system doesn't have a conventional earth conductor, just Ls + N - customer's "earth" are connected to the supply N. If you look at what happens as the mains cable wends its way down the street you'll see that the N is connected to everyone's pipework by bonding (or c.p.c.s) and the pipework also runs down the street - so the supply N is electrically connected in parallel with the public gas and water pipework (where it's still metallic). So supplier's N current (both from your installation and neighbouring ones) flows not just in the supplier's N conductor but a proportion of it in the pipework too - via bonding conductors. A smaller proportion may also find its way back to the supply's star point via the general mass of the earth. So the bonding conductors can carry a sometimes significant current, and for long durations. That's why we're told to use larger bonding conductors (i.e. starting at 10mm2) for PME.

Of course the actual size of this 'diverted N' current depends on loads of factors we can't control - the amount of current flowing in the the supply N to start with - which depends on the neighbourhood loads and (if 3-phase distribution) how well they're balanced; the relative impedances of the supplier's N and pipework, physical layouts and so on. Mostly currents are relatively small, sometimes they're big enough to start very significant fires (look back at some of JP's posts).

I suspect that UKPN's point was that whatever the state of the bonding, it's been like that for a long time and hasn't burned down yet - thus you might deduce that the amount of diverted N current in the neighbourhood is relatively small. I guess the counter argument to that is rather like the warning often given with financial products - past performance is no guarantee of future returns - i.e. whatever the state of the network today, there's no guarantee that it'll be the same tomorrow. Neighbours can introduce new loads (or remove some), very occasionally the lads in a van might actually get out, dig a hole and make an alteration to the network (either cables or pipes) and change the balance of things very significantly.

- Andy.
 07 August 2014 11:33 AM
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NRG32

Posts: 9
Joined: 27 November 2013

AJ. excellent explanation.
( I looked for JPs posts, but sorry cant find them. Is he the author of the posts?)
Any way it has me thinking are these stray currents making there way into the system via the shared neutral or the extraneous metal work or both?
What could be the rating of these strays?
Why aren't they dispersed through the earth?
Any way im sure ill find these answers with a bit more research (time permitting!).

I have heard of surges taking out TVs and electronics on PME systems and wonder if this id due to non existent main bonding.

I know that in this case that the house is on a small street in a small residential estate with no industry or room for it. There has been no incidents as far as I am aware relating to electrical fires over 40 years.

My objective is to attempt to install a main bonding cable. But this could be disruptive since the water and gas services are at the back of the house and the MET at front. Im looking at disturbance to decoration and 40m cable run through loft.

My dilemma is is it justifiable. Can I make an educated decision not to upgrade and. Am I satisfied that the installation is safe (I was!). And what code do I put on the EICR?
 07 August 2014 01:51 PM
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perspicacious

Posts: 7235
Joined: 18 April 2006

"Any way it has me thinking are these stray currents making their way into the system via the shared neutral or the extraneous metal work or both? What could be the rating of these strays? Why aren't they dispersed through the earth? Any way I'm sure I'll find these answers with a bit more research (time permitting!)."

Refresh yourself on Kirchhoff's First Law and have a look at Fig 3.9 in 312.2.1.1. Add extra earths to the exposed-conductive-parts of the consumer's installations and link the four earths together with say 40 Ohm resistors. Then add say 0.03 Ohms between the nodes shown on the PEN conductor. Now show 60 A flowing in the PEN conductor of the single phase installation and using Kirchhoff's First Law, put the magnitude (and direction) of the current flowing inbetween the nodes.

Regards

BOD
 07 August 2014 03:12 PM
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AJJewsbury

Posts: 11467
Joined: 13 August 2003

I looked for JPs posts, but sorry cant find them. Is he the author of the posts?

I can't find them either at the moment! Maybe JP will look in and remind us. I'm sure there was one where PME bonding had been connected on a temporary site. There was this one http://www.theiet.org/Forums/f...tid=205&threadid=48343 too, but that was exacerbated by the supply N being completely open circuit so the bonding took the entire N current rather than just a proportion of it, which isn't really typical.
- Andy.
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