Dave Osborne wrote:
Toby wrote:



He is digging the trench now, but isn't sure about the depth - it will
run under some slabs of a patio, then under the back of a flower bed -
am I correct in thinking there isn't a finite depth required, it just
needs to be at a sufficient depth to avoid being damaged by any
reasonably foreseeable disturbance to the ground?


The minimum depth, as you say, is a moving target depending on a
risk-based likelihood of the cable being disturbed.

The minimum specified by DNO's for service cables is 450mm *to the top
of the buried cable or the duct containing the cable*, so you will need
to dig deeper than this to lay sand under the cable/duct and allow for
the diameter of the cable/duct.

Under agricultural land (where there is a likelihood of ploughing
activity) the depth requirement can be as much as 1000mm to top of
cable/duct.

see he http://preview.tinyurl.com/d8lswg

Pages 9-10

Just found another DNO document which specifies a trench depth of 530mm
for domestic new connections. They say that for a direct burial they lay
their cable in the bottom of this trench, but I suspect they are
allowing for an 80mm dia. duct to bring the top of the duct to 450mm
below finished level.