Exporting PME

[suffolkspark]

hi there guys first time post so be kind some help to solve an argument at the work place.
1. what is the general rule on exporting PME to an outbuilding am i right in think its ok with TNCS but a no-no with TNS.
Does TNS need a stake at the outbuiding with a 30mA RCD, Where in the regs does it say any of this because i cant find it

2. could flex be used as fixed wiring, as in chased in the wall like you would with a T+E etc

 

[electronicsuk]

hi there guys first time post so be kind some help to solve an argument at the work place.
1. what is the general rule on exporting PME to an outbuilding am i right in think its ok with TNCS but a no-no with TNS.
Does TNS need a stake at the outbuiding with a 30mA RCD, Where in the regs does it say any of this because i cant find it

You wont find such a regulation because it doesn't exist. TN-C-S and TN-S earths can both be exported, but the regulations do specify certain special circumstances/installations where an installation MUST be TT, such as in certain places on farms where animals are likely to be in close proximity to the installation.

2. could flex be used as fixed wiring, as in chased in the wall like you would with a T+E etc

Yes, although there is a regulation stat states that the conductors of fixed wiring must be of a minimum CSA. I can't remember it properly off-hand and I don't have my copy of the regs within reaching distance, but I believe it's 1.0mmsq.

 

[Taylortwocities]

This article deals with this in some detail. http://www.theiet.org/publishing/wiring-regulations/mag/2005/16-elect-inst-outdoors.cfm?type=pdf

Note this is pre-17th edition but most of it is relavent.

 

[LoveRocket]

hi there guys first time post so be kind some help to solve an argument at the work place.
1. what is the general rule on exporting PME to an outbuilding am i right in think its ok with TNCS but a no-no with TNS.
Does TNS need a stake at the outbuiding with a 30mA RCD, Where in the regs does it say any of this because i cant find it

2. could flex be used as fixed wiring, as in chased in the wall like you would with a T+E etc

1. TNC-S is PME, TNS is TNS. There's no such thing as "TNS PME"
If you're using an earth rod then it's not TN is it? It's TT.
The RCD requirements depend on what circuits are installed in the outbuilding, the fact that it's an outbuilding makes not a jot of difference.

2. Yes.

 

[suffolkspark]

iam aware TNC-S is PME, don't think i said TNS PME any where??

with regards to the earth rod iam refereing to the out building its self, TNC-S in the house,
i was unsure if you had to just take the L and N and stake or it was within regs to take a for example 3core L N and CPC
Thanks Taylortwocities for the link, has anyone else got a 17th version, iam aware it could possibly be the same

 

[LoveRocket]

The first thing you said was

1. what is the general rule on exporting PME to an outbuilding am i right in think its ok with TNCS but a no-no with TNS.

I read that as "can I export PME on TNC-S but I can't export PME on TNS", which is why I corrected you.

If you use an earth rod at the outbuilding becomes TT.

To get at what I think you're asking, you can export a TNC-S earth, but you must export the equipotential zone by means of a full sized MPB conductor.

 

[ban-all-sheds]

I read that as "can I export PME on TNC-S but I can't export PME on TNS.

That's what he said.

What with that, and his other questions, I am really struggling to understand why he calls himself suffolkspark...

 

[suffolkspark]

Ok sorry, my wording wasnt the best in my first post.
With regards to calling my self Suffolkspark, I have been qualified for 2 years now and iam still learning and iam sure yourself will admit you can't know everything and as I couldn't find it in the regs anywhere I just 4t I would ask, I read stuff on here and find some stuff on here interesting and know there aresome experienced sparks on here .

 

[LoveRocket]

Ok sorry, my wording wasnt the best in my first post.
With regards to calling my self Suffolkspark, I have been qualified for 2 years now and iam still learning and iam sure yourself will admit you can't know everything and as I couldn't find it in the regs anywhere I just 4t I would ask, I read stuff on here and find some stuff on here interesting and know there aresome experienced sparks on here .

FarmerSpark (if I may call you that ), nothing wrong with asking questions, but didn't they explain all this to you (it is important safety critical stuff!) at college?Is this "argument at work" between other newly qualified guys, or experienced 'experts'?

You can either export the house earth (be it TT, TNS or TNC-S), but you must main bond any extraneous conductive parts in the outbuilding back to the MET in the house. If TNC-S you must also check with the DNO that they will allow you to export their earth.
OR
You can make the outbuilding TT, and thus it gets its own MET to which you can main bond.

Does that make sense?

Do you understand what we're saying here about earthing? (The last page of Taylor's link is very good)

 

[bongos]

1. TNC-S is PME...

Didn't GaryMo post something on here recently about PNB (as opposed to PME)? They're both TN-C-S...

Sorry i'll take my pedantic hat off.

PNB

 

[LoveRocket]

1. TNC-S is PME...

Didn't GaryMo post something on here recently about PNB (as opposed to PME)? They're both TN-C-S...

Sorry i'll take my pedantic hat off.

PNB

Now THAT, bongos, is outstanding pedantry! Well done, Sir!

I will rephrase my statement: "PME is TNC-S" (Which is true, however to avoid even more pedantry maybe "PME is a form of TNC-S" would be better)

 

[Adam_151]

1. TNC-S is PME...

Didn't GaryMo post something on here recently about PNB (as opposed to PME)? They're both TN-C-S...

I consider PNB to be TN-S, you've got separate neutral and earth conductors from the point at which the neutral is tied down to earth, the only thing that is different from the TNS you see in textbooks is that that point is in the customers main panel rather than the substation. While I can see how you could make the point for it being TNCS, as someone on the IEE forum pointed out, if you did this then people start lumping it in with PME and then it causes complications which dont really exist if you want to export it

 

[bongos]

While I can see how you could make the point for it being TNCS, as someone on the IEE forum pointed out, if you did this then people start lumping it in with PME and then it causes complications which dont really exist if you want to export it

I was only going by what it was described as in the link. I'm not committing either way - i'd never even heard of it until GaryMo posted that link previously.