The 3-wire version works with an isolated and separate rail side, which is connected to the annunciator module and connected to ground via the conductive axles of the vehicles.
Uhlenbrock GBM 43400 Track Occupancy Detector With Relay In Original Packaging
Uhlenbrock GBM-R 432 Track Occupancy Detector New In Original Packaging
Viessmann 5233 Feedback Decoder with Track Occupancy Detector HO
LDT 'MULTI' GAUGE RS-8 8-FOLD FEEDBACK MODULE W/ INTEGRATED OCCUPANCY DETECTOR
