I need to run a SWA 16mm2 cable eiher in the ground at the footings of a garden wall next to a lawn or clipped direct to a north facing wall. The cable will need to come through the cavity wall and follow the edging a footpath and similarly at the side of a tarmac drive. I am happy with 500-600 mm along the lawn at the footings of the garden wall but how deep does the cable need to be buried below the footpath and garage tarmac drive. This has an electric heating installed and I doubt that is 500mm beow the tarmac.