protective equipotential bonding cable size?


Postby ericmark » Mon Nov 10, 2008 1:19 pm

To quote from Electrical Safety Councils web site
“EDQ12 When carrying out electrical work on an installation forming part of a TN-C-S system, is it necessary to upgrade existing 6 mm² protective equipotential bonding to 10 mm²?
EDA12 Not necessarily. If the existing 6 mm² bonding connects all the extraneous-conductive-parts to the main earthing terminal, has been in place for a significant time and shows no signs of thermal damage, then it may not require to be upgraded. Regulation number 701.415.2”.
May be my old age but is not section 701 only to do with bathrooms? Note there is no “supplementary” in wording. I would have been looking at Tables 54.7 which says 16 mm² not 10 mm² and defiantly not 6 mm² for let us remember a TN-C-S supply. I will conceded that with a TT supply or as regulations state not PME then 6 mm² is OK as with regulation 544.1.1 but I was under the impression this was the main problem where the supply authority has changed to supply from TT to TN-C-S then earths also need up-grading have I got it all wrong?
Eric
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Postby kbrownie » Wed Nov 12, 2008 4:39 pm

Hi Eric,
Can't quote from any ref books as have none at hand at moment, but i'm sure Guidance Note 3 recommends that you should evaluate the system being altered and if you consider the system is in good condition and capable of operating safely you can leave it as installed.
KB
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Postby kbrownie » Wed Nov 12, 2008 4:41 pm

Sorry not guidance note 3 guidance note 8
KB
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Postby kbrownie » Thu Nov 13, 2008 12:56 pm

Sorry if a little vague with, requirements in earlier reply, as had nothing to quote from except for what was in my head and the head's a little mashed at moment.
Guidance note 8 refs to additions and alterations which points you in the direction of requirement 130-07-01 BS7671:2001 as guidance note eight has not yet been revised. This regulation number no longer exsists in BS7671:2008 eight but has been given the number 131.8 and worded slightly different.
I know you have the book so I won't quote this regulation.
I hope this offers some clarity to my origanal reply, as far as giving a concise answer to your question i'm unsure.
KB
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Postby ericmark » Thu Nov 13, 2008 5:07 pm

Thank you for your reply. But Guidance Note 8 like the Electrical Safety Councils web site could be sited as a source but not sure if I would except it as complying with BS7671:2008 and the Inspection and testing asks for one to compare against British Standards not some third party authority.

Same applies for lack of earths on lighting. It does not comply with BS7671:2008 and although Electrical Safety Council gives advice on what to do one would still have to mark it down as a non compliance.

However unlike the lighting where they admit it is wrong with the earths they seem to be saying you can use 6mm and if one person has tested then another does the repairs using two standards can cause conflict and to me we all need to be singing from same book.

All best Eric
ericmark


Postby kbrownie » Fri Nov 14, 2008 7:54 am

What your saying makes perfect sense and would be the logical steps, to sing all in tune, and there is plenty of contridiction and lots of grey areas with the many publications out there.
I'm a simple soul and try to stick to the recommend sources, BS7671 and it's guidances. I know they are not legal docs. but they are a branch out of THE EARW and follow the procedures in it.
KB
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Postby ericmark » Fri Nov 14, 2008 12:29 pm

I of course agree with what you as saying.
My point is where I do inspecting and testing of a job done by some one else the big red book is my Bible and if this says it required 10 or 16mm earth cable and the electrician had fitted 6mm earth cable I would flag this up as a fault.
Because it is common in this area to find properties which were originally TT and are now TN-C-S it is common to find the earth wires have not been up-graded at the same time.
Since normally the 100ma RCD is still in place or if the consumer unit has been changed two 30ma RCDs have replaced it I know in real terms there is no problem with 6mm earth cable. So there is a lot of sense in what the Electrical safety council have said although they do not stipulate that the RCD must be left in place.
If I did not flag up the fault and in the future some one else notices the non compliance then it could cause problems for me. But if the electrician had read the electrician safety councils statement he would be waving that at me and saying look its OK they say so why have to raised this as a fault.
Years ago we did what we felt was safe and before 1991 then the IEE regulations were made into a British Standard the regulations were only considered as a guide. Now with Part P which unlike other acts like electricity at work act does not say what you can and can't do but refers you to BS7671 thus making it law. The guild to 16th Edition did make me laugh a little fancy having a guide to a guide? In real terms it was not a guide more an Appendix with items which only appeared in the guide being asked as questions in the 16th Edition exam i.e. number of wires in a conduit. And some of the 15th Edition had been removed from main book and had appeared in the guide instead. Now it seems they have returned to main book with diagrams on what is permitted with a ring main etc.
Some items are a little sneaky like change of "rule of thumb" to "historically" which to me means it was permitted but not now.
If one reads 314.1 you make a comparison with 314-01-01/02 to me all it has done is to clarify the regulation and to show it should include all protective devices not just over current. If one reads it as a clarification rather than new rule than that means its not a code 4 but a code 2 but here we go again nothing in 17th Edition about codes that's all to do with guidance note 4 from electrical safety council.
Oh what a tangled web we weave.
Eric
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