this is taken from something that i am working on right now. it's a 1idejim thing Irrigation circuitry: There are three types of low voltage electrical circuitry involved in irrigation field wiring. Series circuits: An electrical circuit where there is only one path for the electrons to flow. Traditional automated irrigation systems are wired in series. Series systems use one shared common and individual valve wires. Parallel circuits: An electrical circuit where there is more than one path in which the electrons may flow. Two wire systems are wired in parallel which requires much less wire for the wire path itself. Combination circuits: Combination circuits use both series and parallel circuits. We normally see a combination circuit when there are two or more valves wired parallel in a valve box or wired parallel via a splice in the field and connected to a single wire at the controller. To determine what the resistance of the solenoids in a combination circuit is, the solenoid resistance is divided by the number of solenoids wired parallel. Example: Resistance - 30 ohms x 2 solenoids = 15 ohms. Resistance - 30 ohms x 3 solenoids = 10 ohms. These same solenoids wired in series would measure much higher. i hope this helps and doesn't confuse any issues that anyone is involved with right now.