Electrical resistance of concrete

[John Rumm]

While titting about with my wiki article on outside electrics:

"Know your environment

To make a sensible selection we need knowledge of the local environment. The phrase "outbuilding" can encompass anything from a damp draughty shed, to something as civilised as your front room.

Hence establish:

• How damp is the interior likely to get? * Is it easy to make a good contact with earth? (e.g. A concrete floor in a garage that has no extraneous metal parts in contact with earth and no other services like water pipes entering the building will offer a good isolation from earth, whereas a greenhouse sat on damp ground would offer none. "

NT raised the question of ufer earthing (i.e. connecting the rebar in a reinforced concrete slabs, and using it as an earth), and is it really true that a concrete slab will offer good isolation from ground?

that concrete slabs in new builds, and PME supplies are quite common. Also ufer seems to require the concrete to absorb water - something a floor screed at least (being above a DPC etc), is unlikely to do.

Anyone have a take on this?

[meow2222]

AIUI Ufer earthing produces very low earth R for 3 reasons: concrete slabs absorb & store water, staying wet it provides ions in solution it chemically dopes the soil around it, enhancing conduction further

So R of floor surface to ground is going to depend entirely on water content of the slab. If you have a working dpc and no leaks, then R should be high. But that is by no means always so with house crete floors, thre are still lots about that harbour some damp and thus conduct electrically.

NT