Two-wire is a communication methodology between an irrigation controller and solenoids in the field.
Traditional Wiring #
In traditional “multi-wire” communication, an independent wire is installed between the controller and each individual solenoid. A second or “common wire” is connected to each solenoid and closes this electrical circuit. When sending an “On” command to a specific solenoid, its corresponding solenoid wire carries this message to the related solenoid. Only solenoids upstream of a break will operate. If a single station wire breaks to a specific solenoid or the corresponding solenoid fails, then only that solenoid won’t work. This failure makes troubleshooting a single solenoid easy to manage. Broken common wires typically require more diligence and skill to troubleshoot.
One major disadvantage of multi-wire systems is the ability to add new valves in the future. Adding new valves requires a new, dedicated “solenoid wire” to a new solenoid to operate. You can extend Commons wires from the nearest valve box. Extending new wire can be prohibitively expensive in sites with mature landscapes with parking lots or sidewalks.
Two-wire communication incorporates a pair of wires shared between all solenoids in the field. When the irrigation controller sends an “On” command, it broadcasts this message to a corresponding solenoid. A previously programmed “decoder” addressed to the specific solenoid station translates this broadcast message and acts accordingly. While all other decoders will “hear” the message, they won’t act upon the message if the decoder address doesn’t correspond to the adjacent solenoid station number.
Troubleshooting Two-wire systems can also initially be intimidating, but using some simple techniques in the “Troubleshooting” section of this knowledgebase may quickly become your favored product choice.
One advantage of Two-wire communication is when additional valves are needed. The Two-wire path is easily extended anywhere, reducing the cost of site disruption common to multi-wire systems. New decoder(s) are addressed to correspond with any “open” or “unused” stations on the controller. You can do this continuously as long as the maximum number of managed stations is not exceeded.