How often must the system common neutral be connected to a deep earth ground rod?

The correct choice indicates that the system common neutral must be connected to a deep earth ground rod every 1/4 mile. This requirement is rooted in electrical safety standards and practices that emphasize the importance of grounding to protect electrical systems and enhance safety for individuals.

Proper grounding helps to ensure that any fault currents have a path to the ground, minimizing the risk of electrical shocks or hazards. The frequency of connecting the common neutral to a grounding rod is designed to improve the overall reliability of the electrical system and ensure effective dissipation of electrical energy.

Choosing a distance of every 1/4 mile balances the need for safety and practicality. This regular interval allows for sufficient grounding while preventing excessive installation costs and efforts that might arise from connecting the neutral more frequently. Moreover, maintaining this standard helps in reducing the voltage rise in the system under fault conditions and in stabilizing the electrical system against transient voltages.

Other distances, such as every 1/8 mile, would likely lead to unnecessary complexity and expense, while longer distances, like every 1/2 mile or every mile, could compromise the effectiveness of the grounding system. Thus, the choice of 1/4 mile reflects a well-considered compromise in electrical grounding practices.