Quote Originally Posted by The Master View Post
Ive read on the net that there is a need for a 3rd wire to link the grounds together and a shielded wire.
If you do that, then you have to be concerned about ground loops. Read the section on grounding in the B&B app note.

Ground loops are very difficult for most people to understand. If there's any current flow between "ground" points, there can be problems. And, the fact that ground loops can act like a loop antenna with currents induced by electromagnetic fields complicates things even more.