Where should grounding electrodes located under basement slabs or in crawl spaces be installed?

The appropriate location for grounding electrodes under basement slabs or in crawl spaces is as close as possible to the outer perimeter. This positioning helps to ensure that the grounding system is effectively coupled with the earth, utilizing the most stable soil conditions, which can enhance the system's performance in fault conditions. Grounding electrodes need to reliably dissipate fault currents into the earth, and being closer to the perimeter increases the chances of maintaining good electrical conductivity with the ground.

Additionally, placing the electrodes at the perimeter assists in meeting the National Electrical Code (NEC) requirements for grounding systems, which focus on safety and efficiency in protecting structures and occupants from electrical faults and lightning strikes. The perimeter location minimizes the risk of interference from structural elements and improves the overall reliability of the grounding system by providing a more direct path to the earth.