By how much does doubling the length of ground rods reduce resistance?

Doubling the length of ground rods is an effective way to reduce the resistance of the grounding system due to the principle of resistance in electrical circuits. When the length of a ground rod is increased, this effectively increases the surface area that is in contact with the earth, which leads to a decrease in the resistive path for electrical currents.

The resistance of a conductor can be modeled with a direct relationship to its length. Specifically, resistance is proportional to the length of the conductor; however, it is inversely proportional to the cross-sectional area. By doubling the length, the overall resistance diminishes significantly due to the larger area interacting with the ground, effectively increasing the available paths for current to disperse.

In practice, doubling the length of the rod results in a resistance reduction of approximately 40%. This reduction signifies a substantial improvement in grounding effectiveness, which is crucial for safety and performance in electrical systems, especially in substation environments where grounding is critical for protecting equipment and personnel.

Therefore, the correct answer reflects the significant impact of this change on resistance, showcasing an important concept in grounding system design and implementation.