What would be the resistance of a 16-foot ground rod compared to an eight-foot rod?

The resistance of a ground rod primarily depends on its length and the soil conditions around it. A longer ground rod typically has less resistance than a shorter rod due to the increased surface area in contact with the soil, providing a better path for electrical current to disperse into the ground.

In general, doubling the length of the ground rod can significantly reduce its resistance—this is because the electrical current has access to more conductive material, which decreases the overall resistance encountered.

In this case, an 16-foot ground rod will have lower resistance compared to an 8-foot rod, and the resistance of the 16-foot rod is calculated based on empirical formulas and real-world testing that suggest a longer rod would show a notable decrease in resistance. The value of 18 ohms reflects this decreased resistance as compared to the 8-foot rod.

The options provided reflect potential resistance values, and 18 ohms emerges as a plausible answer based on the characteristics of ground rods. This choice aligns well with expectations for ground resistance based on length, hence it being the correct answer for this scenario.