When using a copper grid for bonding, it must not be more than how many inches below finished grade?

The requirement for a copper grid used for bonding to be no more than 6 inches below finished grade is established to ensure that the bonding system is both effective and accessible for maintenance and inspection. A grid positioned at this depth provides a balance between being sufficiently buried to avoid damage and remaining at a depth where it can still be adequately monitored or accessed if needed.

By keeping the grid no more than 6 inches below finished grade, it also minimizes the risk of corrosion or degradation that may occur if it were placed too deep in moist or unfavorable soil conditions. This depth is consistent with safety standards, ensuring that the bonding system effectively performs its role in preventing electrical hazards, especially in the context of swimming pools and similar installations where proper grounding is critical.

The other choices of depths—4 inches, 5 inches, and 7 inches—do not align with NEC regulations and may present issues related to either corrosion, accessibility, or overall effectiveness of the bonding system. This makes 6 inches the optimal and compliant choice.