I am getting a reading of 50 volts between ground and neutral, and ground and hot. In the j-box where the 12-2 romex is connected to the hot and neutral. I disconnected the ground wire in the romex completely. The ground is not touching the j-box or anything else. On the other end of the same romex that feeds a ceiling light I disconnected the ground completely. At that ceiling box I am getting a reading of 120 volts from neutral to hot. When I go from ground to neutral I get 50 volts. And when I go from ground to hot I get 50 volts. Both ends of the ground wire are completely disconnected. Also, I traced the 12-2 romex from the jbox to the ceiling box and there is not a jbox between the two boxes. The 12-2 is laying in the attic exposed and appears not to be damaged. Thanks

Sounds like you have done all that is possible to isolate this ground wire in this cable, it is disconnected at both ends, and no other splices in this cable, completely isolated and located.

To start and help locate the source of this voltage, try shutting off each circuit breaker to determine what circuit, if any, the source of this voltage is. May not be relevant, but good place to start.

If any one breaker does not cause the voltage to go off, shut off all breakers, including the main.

If you can eliminate the voltage, then try doing a continuity test between the ground wire and a known ground, preferably a water line. There should be no measurement.

Can you see the entire length of this cable?

Any chance it is shorted to a water line, or some other grounded system?

Need to try these tests before moving on.

This all assumes you are using a good quality voltage meter.

Sometimes, voltage is induced in a conductor because it runs near a live source.

Sorry but my first thought is, are you sure you have your meter set correctly? An ac circuit will induce a small voltage in an unconnected conductor that runs parallel to other conductors. Perhaps your meter is set to dc volts..