To help understand what a common wire is, we first need to know what components exist in a sprinkler system.
Electrically, sprinkler systems have 4 parts: a sprinkler timer (that controls when the sprinklers should turn on), a valve solenoid (that recieves signal from the timer), and 2 wires; a signal wire, and a common wire.
Purposes of the two wires
You can think of the signal wire as the deliverer of the signal from the timer. The electrical signal from the timer is sent through the signal wire to the valve, which then uses that signal to turn itself open and allow a sprinkler zone to turn on.
The common signal is used to return the signal to the timer. A good way of thinking of this signal is to remember it needs a loop. It goes to the valve, and then needs a separate way home. The electricity in the signal has to be returned to the timer in order to work properly. So the common wire is a one-way street that leads back to the timer.
Why is there only one common wire at the timer?
The wires all basically are going to an "address." Since there are multiple valves (one for each zone), there are multiple wires. Any time a signal needs to go to a specific zone, there needs to be a wire to that zone.
Conversly, there is usually only 1 sprinkler timer, so only 1 path needs to go to the timer. As this goes in one direction from the valve solenoid to the timer, you can simply use 1 wire to tie all the valves to the single timer.
If there are 2 timers or more on your sprinkler system, you will need a common wire to go to each timer. The wires should make a loop. If a valve is tied to one timer, then a "common" wire should tie back to that same timer.
Still want help?
If you need to have a common wire replaced or installed, call Sprinkler Master at (720) 577-5542 to get help from the masters at sprinkler repair. We're licensed and insured, and know our way around sprinkler systems, so we can get yours up and running in no time!