Grounding Resistance Calculator

NEC 250.56 requires that if a single ground rod exceeds 25 ohms, a supplemental electrode must be added. For most residential applications, 25Ω or less is acceptable. Telecommunications typically requires 5Ω, and sensitive electronics may require 1-5Ω. Industrial and commercial facilities often target 5Ω or less.

Methods include: adding more ground rods (spaced 2× rod length apart), using longer rods, improving soil conductivity with chemical treatment (bentonite or ground enhancement material), using ground plates or ground rings, and ensuring moist soil conditions around the electrode.

Soil resistivity depends on: soil type (clay is lower, sand/gravel is higher), moisture content (wet soil conducts better), temperature (frozen soil is very resistive), mineral content (salt reduces resistivity), and depth (deeper soil may have different characteristics).