Martin Carroll wrote:

What I meant to say was why should it be buried 50mm below surface?

To circumvent the 17th edition requirement that concealed cables have
"Additional protection" from a = 30mA trip RCD. (protecting the cable
(metal conduit etc), using shielded cable (SWA, Earthshield, MICC, etc),
and surface wiring being other ways.

--
Cheers,

John.

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