HELP with Bonding please

[Sam7]

Hello
I am currently doing an electrical course at college and have a query reguarding TT circuits.

This is the scenario :
For my theory project i have to imagine i'm wiring a detached building.
It will consist of a new Consumer unit ( 1x 6amp breaker and 1x 16amp breaker) which will feed 4 x 2gang sockets in a radial circuit and one Two way light set up (1x Strip light).
The consumer unit it connected to the main house Consumer unit on it's RCD side by 4mm SWA (3 core).

Where i'm stuck is, as the SWA has an earth attached from the main Consumer unit to the New detached building unit, do i connect the Earth OR do i need to install a Earth Rod (16mm Bonding) instead ?

In other words, do i :
A) leave just the Earth from the 3 core SWA attached ?
B) Disconnect the SWA's earth and fit a 16mm bonding to a Earth rod ?
C) Attach both of these ?

I hope i've explained my question enough.
Thank you.

 

[Mac]

Personally i would install an earth rod.Run a 2 core armoured from the house and install a rod.10mm from the earth rod to the consumer unit in the outbuilding.

 

[aiofe07]

how good's the earth from the db, 17th edition would say, if the earth was lost from the supply it would be lost from the garage (outbuilding) so rod, but common sence anyone would use the supply if good enough. Are they looking for your understanding?

 

[Sam7]

Yes i think the question is set for us to try and understand the theory we've been learning.

I thought it would need to be 16mm and not 10mm.
And as the SWA is 3core, we need to work out whether to use the SWA earth or a separate Rod.

or both, but i think this would compromise the RCD protection ? Am i right ?