The Parish Council want to light up a tree that is on the village green for Christmas, I have been given the short straw  on designing the installation.

I have a quote from SPEN to install a unmetered TNCS 0.1 KVA supply to a box on the green and I would appreciate some advice on the bit that will go from the box to the tree and the lights. This will be approx  8 M underground from the supply box with the probability of sandstone a few  inches under the green for part of the route. A small box by the tree may have to be acceptable. The tree is approx 20 ft high and is climbable  from the ground. I would prefer not to have to excavate the sandstone to the normal underground cable depth. The main risks to disturbance would be from tent pegs if someone set up a gazebo for an event or someone decided to plant bulbs.

While I would prefer  ELV for this with the power supply and switching in the supply box most light sets appear to come with a transformer and controller as part of a prewired set unless they are the static always on type which may be acceptable.

If I have to go for a mains supply to the tree I would prefer to run the TNCS supply from the supply box to the tree, with 30mA RCD protection on the cable as nuisance tripping will not be an issue  and have any lighting ELV power supplies / controllers in box by the tree removing the need to TT the final box

Has anyone got words of advice which would help me design/install the above at low cost. While I have experience of  all the individual elements  I feel there may be some issues I am not aware of  in these particular circumstances.  Also I suspect I will be given  the short straw for the FOC installation with a team of volunteers doing the hard work. 

Many thanks