In uk.d-i-y, Stephen Gower wrote:
Could you clarify what I've read on Google groups?

* For an outbuilding, a separate TT earth is required/recommended,
provided by an earth rod.
* The power itself is provided by a 2 core SWA cable carrying live
and neutral.
* The armour of the SWA is connected to earth.

Is this correct,
yup. Exporting the house earth is OK for a garage nice and close to the
house (nearly-attached or just a yard or two away); much further and
the TT route is somewhat better.

................ and to which earth should the SWA armour be
connected, the house, or the garage?

You connect the SWA armour to the house earth: that'll give you the
best (lowest-impedance) path back in the unlikely event of a live-to-earth
fault in the body of the cable (spade, mole with titanium false teeth,
or similar). At the outbuiling end you keep the SWA armour isolated from
the consumer unit - glands to do this are available, or you can just
terminate at an all-insulated CU.

That's the accumulated wisdom I've gathered from this 'ere group!

Stefek