Part P assessment question

[markadams]

One of the questions on a recent Part P assessment was how would I wire an external outbuilding if the earthing arrangement to the property was PME.

I said I would run a three core SWA from the property to the outbuilding and use the cable armour and the third core as the exported CPC.

I was highly criticised and was told that I should install a rod at the property and at the outbuilding.

I can find no mention of this in 17th ed AMD3 book, can anyone tell me where i would find this if it is the case.

I have had a couple of other Assessments previously where they have checked out building installs and never mentioned this so I am not happy.

 

[Midwest]

I've seen that line posted a few times 'Distribution Network Operators may forbid their PME earth being exported from the supplied building' (or similar), but I've never seen it actually written in any DNO document?

 

[ipf]

I've seen that line posted a few times 'Distribution Network Operators may forbid their PME earth being exported from the supplied building' (or similar), but I've never seen it actually written in any DNO document?

….never seen anything done about it, either.

Anyone had any resultant problems?

 

[Wilko]

Maybe concerns around a DNO lost N fault causing E rise in both buildings now ?

 

[Midwest]

Supplementary 18th Ed earth rods will sort that

 

[Wilko]

Supplementary 18th Ed earth rods will sort that

I'm not sure how it can. Hopefully I'm wrong, but it seems to me a kettle on a 100 Ohm rod will still pull the touch voltage all the way up. Even 10 Ohms gets to 100V .

 

[Midwest]

I'm not sure how it can. Hopefully I'm wrong, but it seems to me a kettle on a 100 Ohm rod will still pull the touch voltage all the way up. Even 10 Ohms gets to 100V .

 

[telectrix]

we can apply for another sticker for the CU.

"WARNING. THE DNO SUPPLIED EARTH CANNOT BE USED FOR ANY OUTBUILDINGS OTHER THAN THOSE APPROVED BY NICEIC/ELECSA/STROMA/NAPIT/E.T.

 

[Richard Burns]

E.T.?

 

[Dave OCD]

I'm not sure how it can. Hopefully I'm wrong, but it seems to me a kettle on a 100 Ohm rod will still pull the touch voltage all the way up. Even 10 Ohms gets to 100V .

On a 30ma RCD ?

 

[Ian1981]

I'm not sure how it can. Hopefully I'm wrong, but it seems to me a kettle on a 100 Ohm rod will still pull the touch voltage all the way up. Even 10 Ohms gets to 100V .

I think they where looking for a reading of around 20 ohms for the supplementary earth electrode, similar to that of the DNO electrode at the supply end

 

[Dave OCD]

Good luck with that ! Here in Cornwall last week I drove in 2 x coupled 5/8 rods 8 feet in total and got 144 ohms !

 

[Ian1981]

I can’t confirm if that’s gospel but I think that’s one of a number of reasons why it’s been shelved for now anyway.
I heard the 20 ohms figure from an NICEIC webinar.
Yes I said it NICEIC !!
The guys that make the rules

 

[Deleted member 26818]

For street furniture to be allowed connection to the supply PME connection point in the LEB area, it used to be RA of 10 Ohms.

 

[Dave OCD]

All the streetlighting in Cornwall is on PME.

 

[Deleted member 26818]

All the streetlighting in Cornwall is on PME.

Electrode on the penultimate column.