UK Advice needed for garage power job

[westward10]

due to not being allowed by dno to transport pme to other buildings and or high earth readings,

You are not exporting PME at all, what you are doing is extending a circuit to another building which happens to be derived from a PME source.

 

[drilltoaster]

I’m not sure any DNO have any reservations on exporting/extending pme supplies in a domestic installation.

What Scheme are you with?

niceic
IF the outbuilding has NO exposed conductive parts & thus no introduced low resistance earth path then the PME can be exported.
e.g. total wooden shed on support battens with no pipework entering the shed...
This will meet BOTH of the above regs so OK exported.
Obviously if the house supply was TT or TNS the max fault current down the earth conductor would NEVER be the full load current. e.g. a broken neutral in these situations would just mean NO power!https://talk.electriciansforums.co.uk/uploads/emoticons/default_plain.gif
so only a smaller CSA earth needed to safely export earth.

which is why i said check not a must do.

 

[westward10]

You don't want to be listening to the non-collective opinions of the NICEIC. The presence of extraneous conductive parts is irrelevant providing the cpc of the supply cable to the building is adequate to support main protective bonding.

 

[Pretty Mouth]

western power is my area and ive been shoulder tapped by my governing body before on a visit
tt allows for higher than 35ohms at db

Hi drilltoaster, I've had a good look into the whole 'DNO forbids exporting PME earth' thing, and it would appear to be a myth. I can find no evidence that any DNO outright forbids it, and neither can anyone else when challenged.

For western power, the best information I can find comes from their website, click on 'Can you provide an earthing terminal'

Western Power Distribution - Information for electrical installers

Western Power Distribution is the electricity distribution network operator for the Midlands, South Wales and the South West. You can contact us 24 hours a day, 7 days a week, 365 day a year.

www.westernpower.co.uk

In short, if everything meets BS7671 and Engineering Recommendation G12 then you're good to go.

http://www.dcode.org.uk/assets/uploads/ENA_EREC_G12_Issue_4_Amendment_1__2015_.pdf

 

[goasis]

Can someone explain to me what this phrase "exporting PME" actually means, and if it is actually mentioned in bs7671?

 

[davesparks]

Can someone explain to me what this phrase "exporting PME" actually means, and if it is actually mentioned in bs7671?

I think it strictly means selling PME to another country, which is utter nonsense.

It is a phrase used incorrectly, usually by people who get their knowledge from rumours and what their mates tell them in the pub, to refer to extending the equipotential zone of a PME installation to outbuildings.
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western power is my area and ive been shoulder tapped by my governing body before on a visit
tt allows for higher than 35ohms at db

A governing body tapped you on the shoulder???

Do you mean the assessor from a competent person scheme talked to you about this and you believed everything they told you without checking the facts and theory for yourself?

 

[drilltoaster]

Hi drilltoaster, I've had a good look into the whole 'DNO forbids exporting PME earth' thing, and it would appear to be a myth. I can find no evidence that any DNO outright forbids it, and neither can anyone else when challenged.

For western power, the best information I can find comes from their website, click on 'Can you provide an earthing terminal'

Western Power Distribution - Information for electrical installers

Western Power Distribution is the electricity distribution network operator for the Midlands, South Wales and the South West. You can contact us 24 hours a day, 7 days a week, 365 day a year.

www.westernpower.co.uk

In short, if everything meets BS7671 and Engineering Recommendation G12 then you're good to go.

http://www.dcode.org.uk/assets/uploads/ENA_EREC_G12_Issue_4_Amendment_1__2015_.pdf

i never said forbid
i got a dilemma for you
2 core swa installed in ground by house builder (major builder) already supplying a db in garage ze is 175 ohms what do you do?
scenario
customer wants a new consumer unit installed in the detached garage.
main incomer to building is on other side of house approximately 20 mtrs away new cable route if required is via grass and concrete, clay and rock is located in ground approximately 18inches if lucky.

 

[drilltoaster]

i never said forbid
i got a dilemma for you
2 core swa installed in ground by house builder (major builder) already supplying a db in garage ze is 175 ohms what do you do?
scenario
customer wants a new consumer unit installed in the detached garage.
main incomer to building is on other side of house approximately 20 mtrs away new cable route if required is via grass and concrete, clay and rock is located in ground approximately 18inches if lucky.

i forgot to mention current ze is armour cpc

 

[davesparks]

i forgot to mention current ze is armour cpc

What on earth is that supposed to mean?
Ze is the EFLI of the DNO's service, it does not include any part of the installation.

 

[goasis]

i forgot to mention current ze is armour cpc

What's the swa supplied from? Ze is only measured at origin of installation, you're presumably taking about the zs of a distribution circuit.

 

[drilltoaster]

I think it strictly means selling PME to another country, which is utter nonsense.

It is a phrase used incorrectly, usually by people who get their knowledge from rumours and what their mates tell them in the pub, to refer to extending the equipotential zone of a PME installation to outbuildings.
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A governing body tapped you on the shoulder???

Do you mean the assessor from a competent person scheme talked to you about this and you believed everything they told you without checking the facts and theory for yourself?

it was a long time ago and yes while being assessed working for someone else and i had the unlucky visit with the company manager aswell so never really looked into it.
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What's the swa supplied from? Ze is only measured at origin of installation, you're presumably taking about the zs of a distribution circuit.

20a mcb at board db1 measured at db2 rewirable fuse metal clad board

 

[goasis]

it was a long time ago and yes while being assessed working for someone else and i had the unlucky visit with the company manager aswell so never really looked into it.
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20a mcb at board db1 measured at db2 rewirable fuse metal clad board

What's the supply earthing arrangement? & the actual ze?

 

[westward10]

I assume you mean Zs not Ze as it is in the garage. If you have a Zs of 175 ohm then the circuit to the garage needs addressing as to why it is so high.

 

[drilltoaster]

What's the supply earthing arrangement? & the actual ze?

pme and ze at db1 if my memory serves about 22 omhs

bottom end i couldn't rely on the swa cable earth so installed a rod and isolated the gland earth connection at garage to stop parallel paths

 

[davesparks]

ze is 175 ohms what do you do?

Contact the DNO and get them to fix the high Ze.
No matter what you do with the garage supply the Ze will still be 175

 

[drilltoaster]

Contact the DNO and get them to fix the high Ze.
No matter what you do with the garage supply the Ze will still be 175

i think we have covered to issue i miss abbreviated Ze as Zs

 

[davesparks]

pme and ze at db1 if my memory serves about 22 omhs

bottom end i couldn't rely on the swa cable earth so installed a rod and isolated the gland earth connection at garage to stop parallel paths

If the armour is not in good condition then the cable is damaged and must not be used. Installing an earth rod will not fix a damaged SWA cable.
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pme and ze at db1 if my memory serves about 22 omhs

If the Ze is 22 ohms you still need to contact the DNO as it is way above what is acceptable.

 

[goasis]

That Ze needs addressing, and unless the swa is miles long, surely there is some reason why your zs is so massively high that you could look, into? Loose terminations or something? I'm not sure the solution to an unexpected Zs is to stick an earth rod in.

This is a slightly different scenario to the Op.

 

[drilltoaster]

If the armour is not in good condition then the cable is damaged and must not be used. Installing an earth rod will not fix a damaged SWA cable.
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If the Ze is 22 ohms you still need to contact the DNO as it is way above what is acceptable.

sorry 0.22 my bad (trying to quote and not preproofing what i reply)
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That Ze needs addressing, and unless the swa is miles long, surely there is some reason why your zs is so massively high that you could look, into? Loose terminations or something? I'm not sure the solution to an unexpected Zs is to stick an earth rod in.

This is a slightly different scenario to the Op.

i wasnt looking to get roasted here i just put something out there and asked them to check

 

[goasis]

Ah, that seems more reasonable, that high zs would still need some investigating I think, using the armour as cpc would not account for that reading, and this situation doesn't mean that every outbuilding install needs an earth rod.


Not meaning to "roast" you buddy, I certainly don't know it all, just having a discussion... ?