Granny Annexe

[Newpark7]

Hi All

I have to quote for wiring out an attached extension which will be used as a Granny Annexe, this will contain a small kitchen area & shower room. If I use a Henley block at the cut-out and run a 16mm T&E cable via a Switched Fuse to a separate CU for the Annexe will I need to provide Bonding in the Annexe? as the Main Services I.E. Water & Gas are already bonded in the house.

It is a TNC-S system. Also will the 6mm CPC of the T&E be sufficient if connected to the MET to serve the Annexe.

Thank you

Regards Newpark7

 

[davethsparky]

You need to calculate the size of the CPC required as per one of the standard methods. Either calculate using the adiabatic equation, or use the table which says anything up to 16mm requires a cpc of equal size to the live conductors.

You may need to provide bonding, but then again you may not, you need to assess whether or not there are extraneous parts accessible.

 

[Geoffsd]

or use the table which says anything up to 16mm requires a cpc of equal size to the live conductors.

Not disagreeing - but only applies to the required size of conductors, not to unnecessarily oversized ones.

 

[davethsparky]

I don't follow, who on earth would be installing unnecessarily oversized conductors? It would be unnecessary!
We can only assume that the 16mm has been calculated as the necessary size and therefore the cpc could be sized as 16mm in accordance with that table.

 

[telectrix]

i'd use 16mm SWA. 1. the cpc is then adequate. 2. it don't need RCD protection. also, if water and gas services come from the main house pipework, they're already bonde, provided there's no plastic in the water pipes between the house and annexe.

 

[Geoffsd]

I don't follow, who on earth would be installing unnecessarily oversized conductors? It would be unnecessary!

Precisely but lots do - see number of post saying "I always replace tails with 25mm. when changing CU".

If this annexe is having an 80A supply then 16mm sub-main will be required.
However, if 60A switch-fuse is fitted then 10mm would be sufficient - and/or used for cpc sizing (if not calculated) and half of that (except TNC-S) for bonding.

We can only assume that the 16mm has been calculated as the necessary size and therefore the cpc could be sized as 16mm in accordance with that table.

We can but hope.

If as you suggest the 16mm is oversized unnecessarily then I suggest the bloke is an idiot and may want to consider a career change to something befitting someone of lesser intelligence, painting and decorating for example.

Can I quote you the next time it arises?

 

[decolad69]

I don't follow, who on earth would be installing unnecessarily oversized conductors? It would be unnecessary!
We can only assume that the 16mm has been calculated as the necessary size and therefore the cpc could be sized as 16mm in accordance with that table.

If as you suggest the 16mm is oversized unnecessarily then I suggest the bloke is an idiot and may want to consider a career change to something befitting someone of lesser intelligence, painting and decorating for example.

* Unnecessary comment removed*