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Topic Title: 18th EDITION DPC
Topic Summary: NOW LIVE
Created On: 02 June 2017 10:55 PM
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 12 June 2017 07:03 PM
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Legh

Posts: 4028
Joined: 17 December 2004

Thanks Mike....
I had it and then lost it and then found it again but only the abbreviated contents.......
It states that it is a long document which doesn't respond well when using explorer 10 and advises all to use Chrome or Firefox.......
So, I think that now we've dealt with the most important topics we need to move onto the next colour of the cover ! ........

Legh

-------------------------

http://www.leghrichardson.co.uk

de-avatared
 12 June 2017 08:33 PM
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sparkingchip

Posts: 9953
Joined: 18 January 2003

Still looking for a computer to view the document?

You are not alone!

Andy B
 13 June 2017 11:21 AM
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Bhilly

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Appears to have gone totally AWOL now - just says "server error"
 14 June 2017 05:51 PM
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AJJewsbury

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There look to be some significant changes to section 708 too - if my quick read is accurate then it's widened in scope to apply to hard-wired supplies to static caravans (residential park homes) as well as traditional tourers and tends. Also the pitch sockets will have to be interlocked (which will presumably mean quite a design change for the traditional outlet box with the protective devices in the middle and to to four simple sockets on the sides).
- Andy.
 17 June 2017 04:11 PM
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weirdbeard

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bump!

-------------------------
:beer)
 17 June 2017 04:59 PM
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sparkingchip

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This consultation is null and void as far as I can see as the document is completely unusable in its current form.

I assume it is supposed to be the entire book, rather than just the edited highlights of the proposed revisions is being presented in a way to stop people saving or printing a copy, but this has made it unusable.

Perhaps the document should be taken down and replaced with edited highlights, then if someone wants to comment on something that is not included in the proposed revisions they can email it in.

Because it is not going to be a relevant consultation.

Andy B
 17 June 2017 05:37 PM
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sparkingchip

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With one hell of a lot of perseverance, I managed to comment on 542-1-201 the requirement to supplement the suppliers earth with an a direct earth.

542.1.201 The main earthing terminal shall be connected with Earth by one of the methods described in Regulations 542.1.2.1 to 3 , as appropriate to the type of system of which the installation is to form a part and in compliance with Regulations 542.1.3.1 and 542.1.3.2 . Additionally, there shall be an earth electrode, supplementing any earthing facility provided by the distributor, in accordance with one of the requirements of Regulation 542.2.3, to prevent the appearance of a dangerous touch voltage in the event of the loss of the main connection to Earth.

Maybe I haven't got the drift of it, anyway my comments are:


First,there is a total lack of clarity to this regulation.

Secondly, without a requirement for a RCD main switch upfront of the complete installation is it achievable?

I won't be making anymore comments, lifes too short!

Andy B
 17 June 2017 06:43 PM
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sparkingchip

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I cannot see that a TN installation reverting to TT if there is a broken PEN without some sort of voltage operated or earth leakage breaker upfront can limit the dangerous voltage to 50 V, so unless dangerous voltage is defined at a higher level in BS7671it is really not going to be generally achievable.

Andy B.
 17 June 2017 07:03 PM
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dustydazzler

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I might have got completely the wrong end of the stick here , but chatting to a sparks this morning at my local trade counter he is being told 'not' to reconnect the pme earth to the consumer unit on a board change. But to TT the property.
Errrr 'what' I said.......
 17 June 2017 08:22 PM
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sparkingchip

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Originally posted by: dustydazzler

I might have got completely the wrong end of the stick here , but chatting to a sparks this morning at my local trade counter he is being told 'not' to reconnect the pme earth to the consumer unit on a board change. But to TT the property.

Errrr 'what' I said.......


You'll hear a lot of that if this req comes in as trying to achieve a Ra of 200 ohms or less on a earth rod for TT is far more achievable than 1.6 ohms to backup a TNCS earth terminal for a installation with a 60 amp main fuse.

Andy B
 18 June 2017 05:27 PM
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sparkingchip

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Will the Australian standards for installing a consumers earth rod for a MEN earthed installation be followed, as they seem to accept that the the proposed BS7671 requirements are to onerous, indeed the standard does not set a maximum Ra.

Australian standards earth rod testing page 45

Andy B
 18 June 2017 05:55 PM
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mapj1

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Currently if the PEN fails, then neutral current returns via the bonding to metallic services shared with other buildings on the substation that have a functioning supply. That is how it is supposed to work. However if it goes un-detected for years until it kills a plumber changing a stop cock then we have not won. Similar thoughts I presume, drive the recent change to the advice to put insulating breaks into the gas pipes, so large currents which may heat the gas pipes cannot flow.
Now in a building with a plastic water pipe and isolated gas mains this pull down path is removed. I think the thinking is that the earth rod is some kind of replacement, as there is a history or electrodes making open circuit street lamps and similar that would otherwise be lethal, just tingly. This works as street lamps present a small and well defined load. A house or group of houses with 100A supply are quite different.
BUT, while it will work if you only have the landing light on, the first person to plug in a kettle, is likely to liven up all the metalwork in the house as before, and now we have the additional problem of a square meter of live ground in the front garden or whatever.

While many square metres of hammer driven steel piling might be a pretty good ohm or two earth, a post build addition of an electrode of a hundred ohms or so is likely to be about as much good as holding down the house voltages against even 3kW of load as towing a Landrover using knicker elastic - all the tension is across the thing least able to handle it.

As regards the AU/Z document linked above I find the introductory sentence in 3.10.3 to be very telling.

-------------------------
regards Mike


Edited: 18 June 2017 at 08:59 PM by mapj1
 19 June 2017 01:47 PM
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sparkingchip

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This is for both TNS and TNCS earth terminals.

In the case of TNS it would simply become a TT installation, however it will then need RCD protection to provide protection against indirect contact, but presumably the neutral may be intact so protection against direct contact is unaltered.

The real problem is TNCS as presumably if the earth goes then the neutral goes with it and everything bonded gets livened up possibly to mains potential without trippping RCD devices.

What is considered a dangerous voltage and now low does the resistance have to be on these new earth electrodes? Until we have this information we cannot really judge what the requirements are, however as of the moment I will say it is unachievable in the majority of installations without considerable electrical installation work that will be intrusive and expensive for clients, whilst the benefit of solving a problem that is generally not a problem will not justify the work.


Andy B
 19 June 2017 02:12 PM
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dustydazzler

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Originally posted by: sparkingchip

This is for both TNS and TNCS earth terminals.



In the case of TNS it would simply become a TT installation, however it will then need RCD protection to provide protection against indirect contact, but presumably the neutral may be intact so protection against direct contact is unaltered.



The real problem is TNCS as presumably if the earth goes then the neutral goes with it and everything bonded gets livened up possibly to mains potential without trippping RCD devices.



What is considered a dangerous voltage and now low does the resistance have to be on these new earth electrodes? Until we have this information we cannot really judge what the requirements are, however as of the moment I will say it is unachievable in the majority of installations without considerable electrical installation work that will be intrusive and expensive for clients, whilst the benefit of solving a problem that is generally not a problem will not justify the work.








Sums things up nicely



Mic drop
 19 June 2017 05:36 PM
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weirdbeard

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Originally posted by: AJJewsbury




It would appear we will have to wait until MondaY.


seems we're still waiting, still BSI have acknowledged the problem at least...


Update: 5 June 2017



Apologies - due to technical issues the draft of BS 7671 is not yet available for comment on this site. We are working to resolve this issue as soon as possible. Please check back for an update later today.


Regular readers might remember 5th of June was the expected date given in this topic nearly a year ago and despite the IT problems suffered by the IET and BSI they delivered on time, well done them


http://www.theiet.org/forums/f...id=205&threadid=66046


Originally posted by: burn

Does anyone know when the DPC is to be released?



burn






Originally posted by: NicoleWhitton

Hi burn,



The DPC is expected to be released 5th June 2017 and should be open until 28th August 2017, but we will continue to update you.



Thanks,



Nicole


-------------------------
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 19 June 2017 07:29 PM
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sparkingchip

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Everyone seems to be holding back on commenting about the proposed changes to earthing requirements, , am I the only person who doesn't know who has made the proposal?

Andy B
 19 June 2017 10:30 PM
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Parsley

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The additional earth electrode is probably not an issue where new build is concerned, It is quite easy to sling some buried bare copper around the perimeter of the building wth the civils like they do in France or tie into the ring beam. Surely this cant apply to existing installations? It's not really workable in an existing installations, lots of urban properties don't have access to a garden. It would also be a bit difficult in an high rise flats that was supplied PME by the DNO before BNOs existed.

Regards
 19 June 2017 10:48 PM
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sparkingchip

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So you are potentially going to have an estate of several hundred new houses built all with electrodes when the DNO have just installed a brand spanking new distribution system, that should also have several hundred electrodes.

That's a really worthwhile exercise isn't?

Andy B
 20 June 2017 09:55 AM
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Angram

Posts: 651
Joined: 23 March 2009

Please correct me if I am wrong here.

When I last looked at putting a rod down on PME I found a Guidance Note (not to hand as I write this) giving impossibly low resistance values to bring down the voltage rise to 50v.

On the other hand if a really low value of resistance was achieved there was the chance of excess current flowing in the earth conductor under fault conditions, and a risk of diverted neutral currents in normal working.

What happens in those areas of the UK where the sub soil is sand?

A foundation earth on new builds would involve other trades at an early stage on the site.

Angram
 20 June 2017 10:00 AM
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jcm256

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And Quarries where not recommended PME, well pointless trying to hammer an earth rod into rock anyhow. I see (when got the DPC one time only) that quarries will still come under BS7671.
Could say more but trying to get this DPC is now impossible.

So they are changing from PME to MEN in the 18th.

Protective Multiple Earthing (PME) or Multiple earthed neutral (MEN) systems. In most cases these types of distribution system also included an earth rod at or near to the point of supply to individual consumers. The main purpose of the local earth rod was to ensure that the neutral conductor would be held at earth potential in the event of a high impedance or break in the neutral conductor. In the even conductor, the load current would return via the earth connection.
IET » Wiring and the regulations » 18th EDITION DPC

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