I would suggest using underground plastic conduit, it's cheap compared 
to the cable, provides considerable protection. Go one size larger than 
the recommend size if possible, makes pulling cable easier. Depth should 
(must) be below your frost line (check your local authorities for this)( 
here in Northern Ohio 3.5' (1M) is required, though I have on 
construction sites encountered as deep as 7' (2M). Don't recommend 
aluminum cable, stick with copper if long term reliablity is important. 
I replaced our 200 amp underground service alum. with copper last 
summer, sure glad it was in 3" plastic conduit. For grounding check with 
your local authorities, or people in the trade. Generally the supply 
houses that deal with contractors and industry know what's necessary.

peter green wrote:
>> I need to have mains (230V) outside the house, at a remote part
>> of the garden, and would like to know if this solution is (a) safe
>> (b) feasible (c) legal [intimate knowledge of NZ law assumed !!]
>>
>> I have plenty of 2-core mains-rated cable - obviously no earth. At
>> the remote end the circuitry will be in a metal box. If I use an RCD
>>
>> http://en.wikipedia.org/wiki/Residual-current_device
>>
>> (which I do when working with tools outside), bang a metal stake
>> into the ground, to which the metal termination box is connected, and
>> put a fuse on Active, is this going to pass muster wrt not killing
>> people (especially me) ?
>>     
> i don't know anything about NZ regs but i do have some familiarity with the british ones and your idea screams dodgy as hell to me.
>
> firstly you say nothing at all about core sizes, this matters from 3 points of view: volt drop, disconnect times (with whatever protective device you use) and cable rating.
>
> secondly the cable doesn't sound like its armoured in any way which is going to be a problem if you bury it
>
> thirdly the cables outer sheath is unlikely to be suitable for long term outdoor use especially if the cable is white (black pigments tend to block UV penatration, thats why most proper outdoor cables are black).
>
> finally earth rods (if considered an acceptable as a means of earthing where you are) are not a DIY job to install. Its all too easy to end up driving d into ground that is not very conductive.
>
>
>   
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