David,
I was aware of the PVC/Polystyrene interaction.
A new sort of TPS cable has just been released over here that has been especially formulated for contact with Polystyrene foam.
SWA cable never really caught on over here, if you do want to use it for anything, it is horrendously expensive.
We use concentric wound Neutral-Screened PVC or XLPE cables for underground services here, with XLPE being used exclusively above 3.3kV.
Paul,
I've seen the garden hose installation and the direct burial too!.
One guy even laid all the wires under the concrete slab in his house and just threw the concrete over the top.
This was all well and good, until the plumber went to drill the holes to bolt down the toilet pan. [Linked Image] [Linked Image]