Discuss Power point in external glasshouse in the UK Electrical Forum area at ElectriciansForums.net
#32 shows the amended Reg see the blue book to compare.
That is the way I see it.
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But both 544.1.1 and 54.8 have the caveat "except where PME conditions apply"
That is the crux of the matter.
I take it to mean if the conductors are part of the PME system (i.e. the combined part) then table 54.8 and 10mm^2 or 6mm^2 etc do not apply, and no figures are specified within the wiring regs.
In all other cases - where the conductors have been separated (after the service head) then the conditions in table 54.8 and 544.1.1 are applicable.
If it did just simply mean "except for PME" then that would be the wording.
Why write the clause as particular to PME conditions, if they didn't mean where it is part of the PME (TN-C ) aspect.
Taking "except where PME conditions apply" to mean you can't use that table or regulation when dealing with part of the PME system fits the words, and the fact that the bonding size isn't specified.
Taking "except where PME conditions apply" to mean that the bonding size in the regulation and table isn't applicable to an installation supplied by a PME system begs the questions 1) what cable size should be used as 54.8 is "except where PME conditions apply" so what size for PME; and 2) why the "odd" wording, why not just say 'except for installations supplied from PME"?
I'm at a disadvantage here, as I'm hanging out for a breakfast roll which comes with a free Amendment 2 book, and so don't have the new book yet.
Trying to summarise, for my own benefit, and because this is getting highly confusing, and first looking at the blue book, we have:
-a paragraph about NOT PME, saying main bonding should be 50% of earthing conductor and bigger that 6mm
-a sentence about PME (except highway / street stuff), saying look at 54.8
-a sentence about more that one source of supply.
From the scan above, the new book has exactly the same structure, with one extra bit tacked onto the end of the first point.
The extra bit adds a bit more leeway for the size of bonding in submains.
Am I understanding correctly that the complex debate is whether the new bit applies to all installations, or only 'NOT PME' installations?
I'm not seeing the caveat for 54.8 in blue book or in the scan above - can you help me out?
Trying to summarise, for my own benefit, and because this is getting highly confusing, and first looking at the blue book, we have:
-a paragraph about NOT PME, saying main bonding should be 50% of earthing conductor and bigger that 6mm
-a sentence about PME (except highway / street stuff), saying look at 54.8
-a sentence about more that one source of supply.
From the scan above, the new book has exactly the same structure, with one extra bit tacked onto the end of the first point.
The extra bit adds a bit more leeway for the size of bonding in submains.
Am I understanding correctly that the complex debate is whether the new bit applies to all installations, or only 'NOT PME' installations?
I'm confused - in blue book you are referred to 54.8 specifically "where PME conditions apply"
I'm not seeing the caveat for 54.8 in blue book or in the scan above - can you help me out?
PME conditions is the nature of your supply and the condition is the earthing and main protective bonding requirements satisfy these conditions hence that Regulation does not apply.
I am confused also!
The heading for table 54.8 says 'minimum csa of the main protective bonding conductor in relation to the PEN conductor of the supply' so surely that is the csa of the DNO supply cable combined neutral earth, which as was mentioned previously in a domestic supply would be 35mm or less?
So in @cliffed s case above I would have thought 10mm or equivalent in steel, the combined swa of the cable and cpc would be sufficient to cover that? But then what is the supply connected to wasn't it an existing ring final, in which case the earthing conductor from there would only be 3mm and as such undersize?
My brain hurts!
Ps @mainline I think pages 55 and 56 osg do a better job.
The heading for table 54.8 says 'minimum csa of the main protective bonding conductor in relation to the PEN conductor of the supply' so surely that is the csa of the DNO supply cable combined neutral earth, which as was mentioned previously in a domestic supply would be 35mm or less?
So in @cliffed s case above I would have thought 10mm or equivalent in steel, the combined swa of the cable and cpc would be sufficient to cover that? But then what is the supply connected to wasn't it an existing ring final, in which case the earthing conductor from there would only be 3mm and as such undersize?
My brain hurts!
Ps @mainline I think pages 55 and 56 osg do a better job.
I think this is wandering slightly, from early on in the thread the interpretation of the new Regulation 544.1.1 is what is being brought into question.
The heading for table 54.8 says 'minimum csa of the main protective bonding conductor in relation to the PEN conductor of the supply' so surely that is the csa of the DNO supply cable combined neutral earth, which as was mentioned previously in a domestic supply would be 35mm or less?I am confused also!
The heading for table 54.8 says 'minimum csa of the main protective bonding conductor in relation to the PEN conductor of the supply' so surely that is the csa of the DNO supply cable combined neutral earth, which as was mentioned previously in a domestic supply would be 35mm or less?
So in @cliffed s case above I would have thought 10mm or equivalent in steel, the combined swa of the cable and cpc would be sufficient to cover that? But then what is the supply connected to wasn't it an existing ring final, in which case the earthing conductor from there would only be 3mm and as such undersize?
My brain hurts!
Ps @mainline I think pages 55 and 56 osg do a better job.
Correct
So in @cliffed s case above I would have thought 10mm or equivalent in steel, the combined swa of the cable and cpc would be sufficient to cover that?
It may very well do
But then what is the supply connected to wasn't it an existing ring final, in which case the earthing conductor from there would only be 3mm and as such undersize?
His problem is using the cpc as bonding to the greenhouse.
Page 55 blue osg is switching and page 56 is blank
Last edited:
It isn't a new Regulation it has been reworked so you need to compare both you will then understand the core debate here.
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