Decoder Irrigation System: Advantages And Disadvantages

The conventional way involves a controller with several terminals. Each has a wire to an individual solenoid on a water valve that is electrically-activated. There is a common wire that completes the circuit. It daisy-chains to the other side of the solenoids and goes back to the controller. A 2-wire system relies on pre-numbered decoders. These are usually connected along a common 2-wire path and connected to a solenoid valve.


  • Cable faults of a multi-wire system are easy to diagnose. The fault is usually confined to only one or two valves. The other valves are not affected at all. There is one exception though. That is if it is the common wire that got cut. All valves past the said cut will not be operational.
  • There is also minimal fault finding equipment needed in a multi-wire system. A $20 digital multimeter can be enough.
  • Cable tracing techniques in a multi-wire system can locate lost valves. There is a direct path from the controller that goes to the solenoid.
  • The cabling price for a 2-wire system is much affordable per foot than the multi-wire system. The total project costs are also lower even after factoring in the decoder costs.
  • The installation of a 2-wire system takes less time. It can often be one-third the time installing a multi-wire system. This also contributes to reducing the total costs.
  • Damaged cables are easier and more simple to repair in a 2-wire system. Rejoining two wires is easier than fixing cable bundles.
  • Checking out the entire cabling system takes only about half an hour.


  • A multi-wire decoder irrigation system is simple to understand. Despite its simplicity, it suffers from significant disadvantages. One of which is the cost of the wire. A wire for a multi-wire system can be quite expensive. The installation labor is also not that affordable.
  • Damaged cable bundles are not easy to fix. One needs proper skill and plenty of time to join the cables together. An improper procedure can compromise safety.
  • Adding new valves in a multi-wire system is not easy. One needs to route an extra wire for each new valve. The wire has to go right back to the controller.
  • Some 2-wire systems need a special 14AWG cable. Some of these systems are sensitive to 2-wire cable ground leakage.
  • Locating cable opens, shorts, and ground leakage in a 2-wire system can be challenging. A leakage current clamp meter is always needed by a service engineer. Another essential thing is a fault finding transformer. Diagnosing is easier with these two. A spare solenoid completes the set. The transformer cannot turn decoders on or off by itself.
  • Finding lost valves in a 2-wire system is not easy. Some decoder systems block cable tracing past the decoder. This is often true in systems using DC on the solenoid.