Re: Exterior cables in ground
Cables in the ground are designed to stand in water. Pits fill with water.
In my (UK) experience, the legacy underground copper telephone cables - the major trunk cables with 100 pair / 200 pair - are polyethylene sheathed with a foil wrap as a moisture barrier, then a paper wrap, then the cores with PTFE insulation, and are filled with petroleum jelly.
These are pretty resistant to water, but the polyethylene does become porous over extended time periods.
The bigger problem is where joints are introduced, these are commonly sealed in a Polyethylene tube with liquid resin poured into formers at the cable entries, then wrapped in self-amalgamating tape and latterley heat-shrink tubing. These tend to lose their watertight properties quite quickly.
It's rare,in the UK for armoured cable to be used in ductwork.