Calculates R = (rho / (2 * pi * L)) * (ln(4 * L / r) - 1) for a single vertical anode
For preliminary estimation only, not a substitute for review by a qualified/licensed engineer.
Built for cathodic protection designers who need a rapid, offline way to estimate single-vertical-anode resistance during initial site surveys before committing to complex numerical modeling.
This tool quickly computes the earth resistance of a single vertical anode, providing a crucial parameter for cathodic protection system design. By inputting the soil resistivity, anode length, and anode radius, you can instantly determine the resistance to earth, a key factor in calculating current output and overall system efficiency.
Q: What is Dwight's Equation used for in CP?
A: It provides an analytical approximation of the electrical resistance to earth for a single vertical cylindrical anode in a uniform soil medium.
Q: Why is the condition L ≥ 4r enforced?
A: Dwight's derivation assumes a thin cylinder; when the length drops below four times the radius, end-effects dominate and the formula loses accuracy.
Q: How should I handle layered soil profiles?
A: Use an equivalent weighted average resistivity for preliminary sizing, but verify results with a multi-layer model later.
Q: Can I feed Wenner results directly into this tool?
A: Yes. Convert the Wenner reading to resistivity first (ρ = 2πaR, with the pin spacing a in meters for Ω·m), then enter that ρ here.