Two-wire

Most Two-wire systems only have one 2-wire path linking all of the devices (valves, sensors, pump relays, etc.). Therefore, the size of the irrigation system can help determine which type of technology should be installed. Once a system gets more than 30 to 35 zones, it becomes less expensive to install a 2-wire system. One distinct advantage to 2-wire technology is its expandability. If a new section of irrigation needs to be added to an existing 2-wire system, the path can be tapped into and new irrigation can be added.

Think of a Two-wire system like a phone. Each decoder on the system has a unique number and the controller calls the decoder when it is time to do something.