免费接地电阻计算器
计算接地系统的接地电阻值。
Ground Resistance
35.12 ohm
Ground Resistance vs Soil Resistivity (rho)
公式
## Ground Rod Resistance The resistance of a ground rod depends on soil resistivity and rod geometry. ### Formula (simplified for vertical rod) **R = (rho / 2 pi L) ln(4L / d)** where rho is soil resistivity in ohm-metres, L is rod length, d is rod diameter, and ln is the natural logarithm. Lower resistance is better for safety. Most codes require < 5 ohms for power systems and < 25 ohms for lightning protection.
计算示例
A 3 m x 16 mm ground rod in soil with 100 ohm-m resistivity.
- 01d = 0.016 m
- 02ln(4 x 3 / 0.016) = ln(750) = 6.62
- 03R = 100 / (2 x pi x 3) x 6.62 = 100/18.85 x 6.62 = 35.12 ohm
- 04This exceeds 5 ohm. Multiple rods or soil treatment may be needed.
常见问题
What is typical soil resistivity?
Wet clay: 10-100 ohm-m. Sandy loam: 50-300 ohm-m. Dry sand: 500-5000 ohm-m. Gravel: 1000-5000 ohm-m. Rock: 2000-100,000 ohm-m. Moisture and mineral content have the strongest effect.
How do I reduce ground resistance?
Use longer rods (doubling length reduces R by about 40%), multiple rods spaced apart (parallel combination), chemical soil treatment (bentonite, conductive cement), or ground enhancement materials.
How is soil resistivity measured?
The Wenner four-pin method (ASTM G57) is standard. Four equally spaced pins are driven into the soil and resistance is measured between the inner pair while current flows through the outer pair.
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