Direct Burial Wire
Direct Burial Wire, 18 Gauge.
The only wire (solid core) recommended for automatic systems. It can be used with or without conduit. One central timer can operate valves in many locations. Low current requirements make it possible to have wire runs of up to 500' between AC valves and the timer.
To determine the number of strands you will need, count your valves and add one wire for the common. Thus, a three strand wire is designed for two valves with a common, a five strand wire is used for up to four valves and a common.
If there is any chance of adding a valve in the future, it's a good idea to size the wire for that possibility now.