Does cabling underground corrode over time? We have light posts that don't work and were told that the wiring was simply put in the ground 30 years ago, instead of within 'piping', and that it has become corroded. Wouldn't there be rubber insulation around the wiring? Corrosion would happen pretty quickly wouldn't it ... so that even 30 years ago they would have insulated it in some way ... like with rubber/plastic coatings ... ????