Which factor has the greatest impact on voltage drop in irrigation circuits?

• A. Soil moisture
• B. Conductor length and gauge
• C. Controller brand
• D. Valve color

Answer: (B)

Voltage drop in an irrigation circuit is driven mainly by the resistance of the wiring. That resistance comes from how long the wire run is and how thick the wire is. The longer the run, the more resistance the current encounters, which increases the amount of voltage that is lost along the path to the valve. Using a thicker gauge (lower AWG number) reduces resistance per unit length and lowers the voltage drop. So, for a given number of valves and current, the length of the conductor and its gauge have the biggest influence on how much voltage is lost.

Other factors listed don’t change the electrical resistance of the run in the same way. Controller brand and valve color don’t affect the circuit’s resistance, and soil moisture isn’t a primary driver of voltage drop in the conductor path.