exporting earth

[blenki]

Hi, ive got a new garrage wiring to do , its a tncs system and i do not want to export the earth.Im going to earth the swa at the house but whats the best way to connect to the metalclad CU in the garage without exporting the earth to it.When you attach the cleat at the garage it will automatically earth the CU from the house.Thanks

 

[Spudnik]

Install the SWA into a PVC adaptable box under the CU and run the tails in.

 

[blenki]

Thanks Jason,i didnt want to terminate the swa into a plastic CU for fear of breaking it!.

 

[Deleted member 9648]

As long as there are no other services in the garage which would neccessitate a separate main bond back to the MET,and the garage does not include an area where TNCS is restricted,ie swimming pools...construction site ....temp installation etc..there is nothing in the regs to preclude a TNCS earth in a garage as you describe.
This old chestnut keeps coming up on this forum.

 

[blenki]

Thanks for the reply,ive been in touch with elecsa and the said they have no problem with me exporting the earth.

 

[electric-ian]

Some supply companies don't like you exporting earths, depends where you are.

There is also a note somewhere in one of the books, regs, osg, egwr that says that a pme earth must never be taken outside the equipotential zone. I saw it once but have never found it again!!
Maybe it was hidden in the 16th somewhere...

Anyway, to be safe you can isolate the swa at the garge end with heatshrink or even tape, stick a stake in and an RCD & you cant go wrong.

A downstream RCD to protect the cable is also a good move.

Remember that tails into a metal consumer unit on TT require additional protection so upstream RCD is the best option.

 

[solo2771]

Maybe daft quesion but here goes,
if you have good continuity from met to garage why would you make the garage a tt system?
In my garage i have 10mm feed and a good earth path so why would i want to make it into a tt ?
(more vodka please)

 

[MarcT]

Maybe daft quesion but here goes,
if you have good continuity from met to garage why would you make the garage a tt system?
In my garage i have 10mm feed and a good earth path so why would i want to make it into a tt ?
(more vodka please)

As I see it,the whole issue, in a nutshell revolves around the integrity of the PEN conductor, the possibility of it being compromised by network conditions, and the fact that the DNO don't guarantee it.

 

[Deleted member 9648]

Some supply companies don't like you exporting earths, depends where you are.

There is also a note somewhere in one of the books, regs, osg, egwr that says that a pme earth must never be taken outside the equipotential zone. I saw it once but have never found it again!!
Maybe it was hidden in the 16th somewhere...

So what about an external socket outlet ? Or an outside light ? I'ts outside the equipotential zone...an exported earth...do you put in a separate stake for each of these ??.

Apart from the TNCS locations restricted in the BRB I've never seen anything restricting TNCS in normal installations outside the zone. If anyone can prove otherwise I'll happily admit I'm wrong.

 

[Guest123]

Hi.

A PME system can be exported provided that the either of the following 2 conditions are met

1. There are no extraneous conductive parts within the outbuilding i.e steel frame, water service, gas service etc.

2. If there are conductive parts, then the equipotential zone needs to be extended to the outbuilding via main equipotential bonding conductors sized accordingly i.e a minimum of 10mm2 for each service back to the MET within the house, unless the sub-main is greater than 10mm2 itself.


Some DNO's encourage the exportation of a PME, providing all the relevant conditions are met.

 

[electric-ian]

I love this topic......

Yes, TT maybe over the top, depends on the run and supply cables.

I agree with wirepuller that you cant avoid exporting the earth wiht external sockets, outside lights etc....

Oh and what about that outside tap which is plumbed off the rising main just by the earth clamp!!

Although I did once hear a tale of an NICEIC inspector making a sparky stake each of 7 metal lighting bollards down a driveway - Now that is OTT

All I remember is that my field officer showed me somewhere in one of the books - it was a one liner I think - a note about not takin the PEN conductor outside the EB zone...... I have looked several times but never found it myself since. I will email him and see if he can find it again...

Ian

 

[Deleted member 9648]

Although I did once hear a tale of an NICEIC inspector making a sparky stake each of 7 metal lighting bollards down a driveway - Now that is OTT

Ian

Think I'd have told him (politely) to go forth and multiply

 

[electric-ian]

Think I'd have told him (politely) to go forth and multiply

Or perhaps given him some advice to do with sex and travel..