Inductive pickup (foreign voltage) from even fairly long runs (20kf +) of well maintained copper is usually much less less than half a volt, measuring either T-R, or T-G/R-G. It's supposed to be floating to ground - nothing on a twisted pair should be ground referenced, if you do have voltage to ground, you have a short.

If it was not floating, you'd get atmospherics, hum, and other issues that you saw in old fashioned ground return systems.

Indeed, measurement of voltage and continuity of T-G and R-G is a standard way to check for faulty cable