On 8 Jan, 21:54, The Natural Philosopher wrote:

Probably around 60 years inside a house away from weather.

All depends on whether peeople have "run the cable neatly", i.e. under
the carpet and across doorways, where it gets walked upon.

Back when I worked for BT and did installs we had it drummed into us
where to run cables correctly (i.e. go up and over a door, not under
it), and how important it was to do so even if it made the job longer
to carry out. BT were still planning to be around in 25 years, or even
60 years, so it was expected that it would be _their_ bottom line that
paid to fix the future fault otherwise.

I've not seen this same attitude in commercial phone or CTV cablers,
any time in the last decade (even from BT). Network cablers are a bit
more conscientuous, as Cat5 is itself fussier.