Someone clear this up asap!

[domestic spark]

"Generally speaking the exportation of a TN-C-S supply is the decision of the local DNO and only done with their permission. In the absence of such permission it would be recommended to use a TT system and RCD protection. However most DNO's will allow such exportation to an outbuilding provided it is 2 meters or less in distance from the main
building.

I advise that you check with your local DNO as to their requirements."







2 meters or less in distance from the main
building.

OPEN TO CORRECTIONS BUT, this is stating that, if you want wiring done in garage, conversion etc further than 2 meters from your house, it has to be a TT system??????

 

[DaveyD]

Does this help? http://www.electriciansforums.net/e...l-electrical-forum/28414-exporting-earth.html

 

[domestic spark]

Under the Electricity safety, quality and continuity regulations 2002 you cannot use a suppliers earth to an out building


so every out building has to be tt???

see what i mean, first it fine, then its ok to do as long as garage is no more than 2 meters from house? now its, not allowed at all and must be TT!




NO CLEARER SOMEONE PUT ME STRAIGHT!

 

[Engineer54]

Read this....

A good guide For 'exported PME' and outbuildings!


Where does this ''2 metre'' myth come from, that many keep quoting??
​

 

[DaveyD]

Or this pdf http://www.electriciansforums.net/e...9-good-guide-exported-pme-outbuildings-2.html

 

[domestic spark]

Read this....

A good guide For 'exported PME' and outbuildings!


Where does this ''2 metre'' myth come from, that many keep quoting??
​

BROWSING THE INET and found this quote in many places!

so is exporting tn-cs acceptable? over a distance of 25m? max

 

[Engineer54]

We need Official quotes, not assumptions by those that don't really know!!

It has more of an economical bearing in a domestic situation, when it ceases to become acceptable. Otherwise it has everything to do with cable calculations... Personally i've seen PME taken almost 48 metres, and that was some years ago in Essex. And the owner of the property was and still is a Regional DNO manager !!!!!

 

[domestic spark]

Re: A good guide For 'exported PME' and outbuildings!

A lot of these myths stem from the numerous ''Scaremongers'' of the PME system!! In that ''IF'' (and it's a very big IF) a break in the neutral occurs all connected metal parts will have a potentially dangerous voltage. In reality, the chances of that happening is remote to say the least. I would take a PME system earth out, to any out-building, wouldn't give it a second thought either

Again In reality, what would you rather have as your earth connection, a system that gives you 0.35ohms or a rod at maybe 200ohms, ...i know what i would rather have in my home.

There is no reason why you can't employ a rod on a PME system, in fact many countries insist on it. Many local authorities used to rod TNS supplies to there council houses in the 50s.


i think this clears my questions up!!!!
​

 

[domestic spark]

engineer, presumably a much older wiser man than myself, ran armoured off a pme supply yesterday, 30meters max, tested secondry board where i ran i to and got a reading of 36ohms on ZE. ???????????????????????????????????

thats not good enough? now what?

max is 0.35 right!

 

[Engineer54]

Do you really think 0.01ohms is going to make a difference to your earth fault protection??? I take it you mean't 0.36 ohms ...not 36 ohms??

 

[domestic spark]

0.36 yes, and no i dont, only done 2392 testing course so new to testing, been informed it doent matter anyway as it only applies to orign, i thought that but was admittidly unsure!

 

[Deleted member 9648]

The vast majority of installations in the UK come under Bs 7671.....the only document you need to comply with when choosing the earthing system for an outbuilding is Bs7671. There are no special requirments for ordinary outbuildings in Bs 7671.

 

[malcolmsanford]

The crazy thing about this argument is, as the earth on a TNC-S is the responsibilty of the DNO, it is still their call if they will allow you to export it to an outbuilding, I'm not saying that today they won't allow you but it's best to ask IMO, so just call them. If you don't call them, and export, and something happens you are the one that is going to carry the can.

What is this hatred of TT systems on here.

 

[Deleted member 9648]

Hi Malcolm,
It's not a hatred of TT for me it is just that it is totally unnecessary.As long as the install complies with Bs 7671 and is certified as such,if anything happens the installer is not going to carry the can...it's no different to any other situation.
You can go on and on...what if the earth on a TT goes missing?,they are always vunerable to damage and changing ground conditions,is the installer going to be held to account over that?
The thing I cant fathom is why outbuildings are the only thing people always use to highlight the horrors of TNCS...if you apply that logic it has to apply to all electrical installs outside of the main building,people never seem to ask..."I'm installing an outside light,do I have to rod it?"......yet the same person comes over all unnecessary as soon as an outbuilding is mentioned.

 

[malcolmsanford]

In agreement, but a lot of us more mature guys remember the old electricity supply regulations which IMO were so much more concise as they had a part in them for PME supplies.

I have no trouble exporting the earth, as long as I get assurances from the DNO that they are happy for me to do so. I can say that 99 times out of 100 it would either be "Why are you asking" or "yes".

I still like to make sure that they are happy with this. I would more shocked if the DNO said no, but they may do just that for some reason,

It's not that your doing the install to the regulations, a fault can still develop in that installation, and if you exported the earth without the DNO knowing, and you did have a situation where you had a difference in potential because exporting it was no viable, for whatever reason, then you are held responsible.

It's not a case for me TNC-S then outbuildings TT every time, it's a case of calling the DNO and enquirying if I can export it. IMO though a building that is over 25 metres away from the origin of the supply is more economical to be a TT