A good guide For 'exported PME' and outbuildings!

[IQ Electrical]

For anyone bored by the constant myths and rumours regarding this subject, have a read of this guide from the IEE on supplies to detached outbuildings.

It was published in 2005 but the important bits remain unchanged and might be of some help!

 

[malcolmsanford]

That's what i thought. I have still strapped a 10mm g/y to it though, no harm in that is there?
The supply cable is fed via a 100ma RCD in the house, im moving it off though because other circuits on the RCD side have faults. No harm in having an swa distribution circuit protected by an MCB only is there?

You can always check to see if the pipe is an extraneous conductive part, Attach a wander lead to the MET in the house and via your meter to the pipe and do an IR test. If you get above 22Kohms reading then it is not an extraneous conductive part and therefore you do not need to bond it, and as you say the supply pipe is plastic, there is little chance of it being an ECP.

You say your earth system is a TN-S and the 100mA RCD would make me think that it was fitted to the installation perhaps because the Ze might at one time, or still be high. Have you done a Ze to check? If you do remove the distribution cable from the RCD protection you will need to make sure your Zs is low enough to activate the MCB in time.

 

[IQ Electrical]

22 kOhms is the figure, below this and the part is classed as extraneous.

 

[TinyT]

Zs is good. lower than 0.6 if i recall.

 

[Chr!s]

for a tncs to be PME it is required to be rodded at regular intervals along its length, and also to have a rod as close as is reasonably practicable to the consumers installation, most TNCS in the UK do NOT comply with this requirement, hence they are not proper PME supplies.

I Disagree

I assume this is what you are getting at?
a lot of people mistakenly mix up tncs and pme as being the same supply method, its not,
pme must in its nature be tncs, but tncs does not always have to be multiple earthed.

Agreed, PNB being one variation.

Al.

ESQCR

Protective multiple earthing
9.—(1) This regulation applies to distributors' low voltage networks in which the neutral and
protective functions are combined.
(2) In addition to the neutral with earth connection required under regulation 8(3)(b) a distributor
shall ensure that the supply neutral conductor is connected with earth at—
(a) a point no closer to the distributor’s source of voltage (as measured along the distributing
main) than the junction between that distributing main and the service line which is most
remote from the source; and
(b) such other points as may be necessary to prevent, so far as is reasonably practicable, the
risk of danger arising from the supply neutral conductor becoming open circuit.
(3) Paragraph (2)(a) shall only apply where the supply neutral conductor of the service line
referred to in paragraph (2)(a) is connected to the protective conductor of a consumer’s installation.

 

[oldAL]

Like I said,
even ESQCR doesn't describe a proper PME as recognised by most other developed countries in the world,
have you checked the conditions that are required by 2012 for a TNCS to be called PME ?
I think you may find them somewhat more stringent.

 

[Engineer54]

Like I said,
even ESQCR doesn't describe a proper PME as recognised by most other developed countries in the world,
have you checked the conditions that are required by 2012 for a TNCS to be called PME ?
I think you may find them somewhat more stringent.

You will find that most, if not all new DNO supplies are meeting PME conditions.

Then you have the god knows how many old supply cables, that were previously TN-S but now being converted to PME because of there lead sheath's deterioration etc. There are many such cables, that are in the process of being converted, but do not yet meet full PME conditions. I suppose you could call these situation TNC-S supplies!!! ....Conversion costs money, so it's not going to all happen over night so to speak, but all i'm sure, all will eventually meet PME conditions, just maybe later rather than sooner ...lol!!! .

 

[Chr!s]

Like I said,
even ESQCR doesn't describe a proper PME as recognised by most other developed countries in the world,
have you checked the conditions that are required by 2012 for a TNCS to be called PME ?
I think you may find them somewhat more stringent.

ESQCR is statutory in this country. That is what the law requires.

What other countries do is irrelevant.

IEC 60364-1 which most developed countries base many standards on also describe TNC-S PME in the same way.

What recognised stanard are you referring to ?

Regards Chris

 

[Silly Sausage]

Does anyone know of a decent book for electricity distribution, from generation up to consumers installations, that would explain PME etc etc in a not too analytical way?

It could help with my insomnia...

 

[Chr!s]

Does anyone know of a decent book for electricity distribution, from generation up to consumers installations, that would explain PME etc etc in a not too analytical way?

It could help with my insomnia...

I have a Earthing guide which is not to analytic, other than that try:

"Transmission and Distribution Electrical Engineering"

 

[Silly Sausage]

Thanks...but I might have to take out a second mortgage!
Transmission and Distribution Electrical Engineering: Amazon.co.uk: Colin Bayliss, Brian Hardy: Books

 

[Chr!s]

Archy

Try this link :http://www.eon-uk.com/distribution/...nts/CN East/East Earthing Manual Feb 2002.pdf

Chris

 

[Silly Sausage]

Cheers Chris,

Had a quick scan through, that'll keep me going for a while.
File saved.

Andy

 

[bozobro0]

So i take it this means then that a house that used to be TT but has been upgraded to TNC-S which has a seperate wc in the yard,which some still have,that has a lighting circuit and a cold water feed that normaly comes from the ground has to be seperate from the house, has to have a seperate means of earthing-TT.

 

[SW1970]

This is one of the most interesting threads on the forum!

Here's a variation on a theme. TN-C-S house, twin and earth with small earth conductor to detached garage with no earth rod. What if extraneous-conductive-part is not actually in the garage but is for example, a water pipe on the outside wall of garage (which does not appear inside the garage at all and there are no other e-c-parts inside the garage). Does the need for improved earthing still apply in this scenario? I'm thinking the answer might be yes because user could (e.g.) have a tool plugged into extension lead running into garage. Tool develops fault, and user touches water pipe.

Thanks, SW

 

[IQ Electrical]

This is one of the most interesting threads on the forum!

Here's a variation on a theme. TN-C-S house, twin and earth with small earth conductor to detached garage with no earth rod. What if extraneous-conductive-part is not actually in the garage but is for example, a water pipe on the outside wall of garage (which does not appear inside the garage at all and there are no other e-c-parts inside the garage). Does the need for improved earthing still apply in this scenario? I'm thinking the answer might be yes because user could (e.g.) have a tool plugged into extension lead running into garage. Tool develops fault, and user touches water pipe.

Thanks, SW

The point here is that the pipe wouldn't be classed as an extraneous-conductive part because it wouldn't be capable of introducing a different potential into the equipotential zone.

Because the person using the tool in your scenario would actually be standing on 'true earth' bonding the external pipe to the PME earth terminal would create a greater danger, this is why it was common practice to insert an insulating section in the pipework to external taps on PME installations.