"Dave Plowman (News)" wrote in message
...
In article ,
dennis@home wrote:


"John Rumm" wrote in message
et...
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.

IMO putting it 50 mm deep is a problem. If you are putting something
substantial up you will use screws that are longer than 50 mm so it
offers little protection. It does make it harder to locate using a
detector. I expect its another of those "we haven't really thought this
through but it sounds like we are doing our job" things the IEE comes
up with periodically. I suppose they will try and ban screws longer than
50 mm to fix the problem.

Y es - it's a strange distance. Far more than needed to protect from a
picture hook nail.

Although most things you buy which are designed for screwing to a wall
come with screws which are far too short to make a really secure fixing.

Some of the walls in my house are dry lined.
they have a gap behind the plaster board that can be 50 mm.
That means the cables are 50 mm from the surface and meet the requirements
if they are dropped down and tacked to the wall.
However it offers zero protection as I have to use long screws (120 mm
usually) to get into the wall to fix almost anything.