said by konowl:
Would hate to ever see a response that included a line like well if there are no good pairings then they replace the line.
Cables or parts of cables used to get replaced on a regular basis. Bell cables were designated as either underground or aerial. Both cables can be either buried or in the air.
Underground cables are the most secure, are in many instances in buried conduits for protection and are pressurized from the office with dried air. The largest cables (usually 2400 pair are paper insulated are about 2.5 inches in diameter). Branches can run from these 2400 pair cables and be paper insulated or plastic insulated and can have as few as 200 - 300 pair.
Aerial cables connect to the underground cables at junction boxes in the street at ground level or on poles. A 900 pair underground cable into the junction cabinet could have 4-300 pair and 2-200 pair cables leaving the box.
Aerial cables are the most problematic. They get cut with a backhoe, chewed on by squirrels, are damaged in car accidents, are damaged by telephone company employees and are more prone to corrosion.
While the short list above can impact underground cables; aerial cables are the worst.
The cable in the alley behind our house was replaced about 12 years ago. Squirrels had caused so much damage that the economics was to replace the cable. With FTTH on its way in and the copper being abandoned; Bell will likely have limited the replacement of copper cables to some very specific circumstances. A cable feeding a home probably isn't one of them.