Device Couplers provide easy and practical mechanisms for implementing fieldbus systems. TRUNKGUARD Series 300 Device Couplers (TG300) simplify the use of fieldbus devices in Zone 1 by allowing “live” access for maintenance and eliminating the need for Exd junction boxes. The TG300 Series offers our patented Automatic Segment Termination feature and a key-operated magnetic interlock which permits one spur at a time to be de-energized and worked on without shutting down the entire segment.