pme to tt

[KEVINDOE]

Hi all,

Was hoping for a bit of advice on this,
Existing pme supply to domestic house, a supply needed to a shed, an avery,anothershed then a metal framed shed , all these out buildings are strung down a long garden over 40 meters.
My thoughts were to export pme to a submain, lets say Db1, then switch to TT, feed 1st shed and avery{ just a couple sockets in each}, then, take another ciruit from Db1 to another sub, Db2 and TT with additional rod, to feed metal shed and greenhouse, cstomer has requested that all outside circuits can be isolated from inside the house, so i was thinking of r.c.b.o from ccu ?,, are there any issues regarding r.c.b.o and different earthing systems?, radials to Db1+2 will be 6mm swa burried in ground and surfaceing to subs....
would like some advice please ....as this is my first real post, and i am a new member, could anyone just put a reply in so i know its getting seen ? thanks in advance..

 

[Spudnik]

No need to divorce pme for outbuildings, however, in this instance i would do it a the first DB submain.

 

[KEVINDOE]

Thanks Jason,

do you think it should have its own instalation cert ,,, the TTpart i mean ??

 

[Spudnik]

Each new DB should have an installation cert along with the circuits it supplies.

 

[KEVINDOE]

Sorted !!

thanks again

 

[aptsys]

I wouldn't put an RCBO in the main CU in the house. If you're laying SWA then there's no need to use RCD protection for the cable run. You'll already have a 30mA RCD in DB1 for the TT supply, so you'd have to find a time delayed RCBO anyway to provide discrimination.

 

[KEVINDOE]

Ok, see where your coming from,, my prob is that the customer wants to be able to isolate all outbuildings from inside the house, so i didnt intend using r.c.d in Db1 or 2, just the r.c.b.o to protect the lot ?

does that make sence ?

 

[pushrod]

You could just locate an isolator in a convenient place for the client in the house and keep the rcd for the TT. As there are extraneous conductors in the out buildings i would not export the earth. There are 2 pole lockable ones or i would guess you could use something as simple as a cooker isolator.

 

[aptsys]

You could just locate an isolator in a convenient place for the client in the house and keep the rcd for the TT. As there are extraneous conductors in the out buildings i would not export the earth. There are 2 pole lockable ones or i would guess you could use something as simple as a cooker isolator.

Spot on. I would treat DB1 onwards as a separate installation, and keep your RCD there. Have a switchfuse or isolator/MCB combo at the house to supply the submain.

 

[Guest123]

I'd opt for TT in this situation also, as you mention a steel framed shed and only a 6mm SWA supply.