Bill said:
They are installing an underground electrical cable in my neighborhood. It
has about 20 plastic tubes 4 inches in diameter. I suppose they will have
metal conductors inside. Does anybody know about this design? I suppose it
is about 750kv. What if water gets inside to tube?
Why do you think it is power cables?
Why do you think it is ~750kV? 20 lots of 750kV is rather a lot of power...
It will help cool the cable. Plastic tubes of the ribbed variety often
are just push fit into each other and laid on a sand base. No attempt is
made to keep water out and they often have small slots in them anyhow,
to stop gas build up, etc.. Nice wet ground will take the heat away
better and will probably give the cable a longer life.
If it is power cable, then, you are right, it will have metal conductors
inside. But the metal conductors will be covered in insulating material
and then have stranded steel armour around that, then another layer of
insulation. The tube is covered with sand and a strip of bright yellow
warning tape laid over that. Electricity distribution companies are
rather keen that the electric stays in the pipe.