When paralleling ground rods to reduce earth resistance at a construction site, how far apart must they be placed?

Placing ground rods at an appropriate distance apart is crucial for effectively reducing earth resistance and ensuring proper grounding. The correct answer indicates that the rods should be spaced twice the length of the rods driven into the earth. This spacing allows for optimal performance, as each rod's grounding effect can work independently without interference from adjacent rods.

When ground rods are spaced in this manner, they are more likely to provide a lower resistance path to ground. This is due to the way electrical currents disperse into the earth; sufficient distance between rods ensures that each rod can contribute maximally to the dissipation of electrical energy into the surrounding soil. By adhering to the specified distance, the effectiveness of the grounding system is enhanced, which is essential for the safety and functionality of electrical systems in construction settings.

The other options do not provide the optimal spacing based on grounding principles and may lead to increased resistance or insufficient grounding performance, which is crucial at a construction site where safety is paramount.