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Discuss Earthing conductor csa/size (oh no, not that again I hear you cry) in the Electrical Forum area at ElectriciansForums.net

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Rob Smith 643

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Firstly, appologies for raking this one up again. Although not new to electrical work the earthing arrangements in some properties, including my own, still mystify me.

My home was built in 1997 by Bellway. It has a 60A service head with a 1361 fuse, is TNCS and has a PME sticker in place. The tails are 25mm and the earthing conductor is 10mm. A friend in a younger house in a neighbouring town ((different county and LABC) has the same set up but with a 100A head. His home was built by Barratt.

I have read various threads on the forum that discuss this issue including some fairly heated ones and we appear to have split camp. Some stick to the tables, some prefer the adiabatic equation, some have regard to both but err on the side of caution. And in some cases I doubt that pistols at dawn would have solved it for some parties!

But surely Bellway and Barratt are reputable builders and had their designs/plans passed by different LABC's which might indicate that the earthing arrangement is sound otherwise there are literally hundreds, nay thousands of newish homes throughout the area and possibly the country that were incorrectly wired?

I no longer have my 'red' regs but don't recall any changes with regard to earthing conductors (main) since the arrival of 'green' regs or the subsequent amendment.

Any further thoughts? :dizzy2:

 
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R

RISElectrical

  • Thread Starter Thread Starter
  • #2
With regards PME adiabatic is irrelivent
 
R

Rob Smith 643

  • Thread Starter Thread Starter
  • #3
With regards PME adiabatic is irrelivent
Thats my take on it but knowing that coupled with the existing earthing arrangement is what has created the mystification. :30:
 
O

oldtimer

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  • #4
I would not worry when the 15th came out they wanted to earth bond everything until they got real remember there are 30-40 year old properties with 6mm main earths and nobody is beating down their door demanding it gets changed to 16mm or else
 
IQ Electrical

IQ Electrical

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Why is that?
On a PME supply, the main protective bonding conductor CSA must be selected from table 54.8 based on the suppliers neutral conductor CSA (not the 'tails').
If the installation has extraneous-conductive parts then the earthing conductor will also be subjected to the same table regardless of adiabatic results.
 
M

Mainman

  • Thread Starter Thread Starter
  • #8
On a PME supply, the main protective bonding conductor CSA must be selected from table 54.8 based on the suppliers neutral conductor CSA (not the 'tails').
If the installation has extraneous-conductive parts then the earthing conductor will also be subjected to the same table regardless of adiabatic results.
I was quite happy with earthing until I opened this thread, I'm going for a lie down. Isn't the adiabatic only for the earthing conductor and the cpc? 543.1.1 states that the csa of every protective conductor other than a protective bond can either be calculated or selected from table 54.7. 54.8 is only for bonds on a PME or am I completely off the track?:behead:
 
telectrix

telectrix

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Mentor
Esteemed
Arms
IQ's post is correct table 54.8 relates to main bonding conductors. i still can't see any reason not to calculate the size of the main earthing conductor in accordance with 543.1.3 OR 543.1.4
 
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M

Mainman

  • Thread Starter Thread Starter
  • #10
Never too old to lurn sumfink!!
 
IQ Electrical

IQ Electrical

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On a PME system, the earthing conductor is also a main protective bonding conductor and that is why we are stuck with 54.8 as a minimum ;)
 
D

Deleted member 26818

  • Thread Starter Thread Starter
  • #12
As far as the adiabatic equation is concerned, 10mm² will be sufficient in the majority of cases for supplies up to 100A.
If the main conductors are bunched together or incorporated in a single cable, then a larger CSA may be required for 100A supplies.
In such cases it will depend on the disconnection times.
In general, domestic PME heads are rated up to 100A.
That does not necessarily mean that the main fuse is 100A
 

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