C-H,
Power cables generally have 2 ratings.
The first is the voltage between cores.
The second is the voltage between the conducting cores to earth.
Over here, the cables have a 600V/1000V rating, respectively.
This is for LV reticulation within a Domestic installation, with 2C+E or 3C wiring.
Using this sort of wire in a Distribution system would be frowned upon!.
Use Neutral-Screened or Armoured for Direct Burial.
All stuff we use for Distribution is 1000V/1000V or if you want to be really silly, 33kV/33kV Alu.
Also, all of our U/G stuff is run in 150mm (6") Orange Conduit, regardless of the size of the inside wires, up to a maximum size of conduit of 400mm diameter, for really large feeders. [Linked Image]