This tool calculates the grounding resistance of an earthing system based on soil resistivity, electrode type, and geometric parameters. It helps verify compliance with IEC 60364-4-41 for coordination between earth electrodes and residual current devices (RCBOs). The calculated resistance is compared to the safety voltage limit (typically 50 V or 25 V) to ensure safe operation and proper tripping of protective devices.
| Parameter | Description | Typical Values / Notes |
|---|---|---|
| Type of Ground Electrode | Physical configuration of the earthing conductor | Rod, Horizontal rope, Ring, Mesh network |
| Soil Type | Determines soil resistivity (ρ) | Agricultural (10–150 Ω·m), Clay (50–200 Ω·m), Rocky (1500–10000 Ω·m), etc. |
| Quantity (n) | Number of identical parallel electrodes | Must be ≥1; affects total resistance via parallel reduction |
| Length (L) | Total buried conductor length | Rod: depth; Rope: linear length; Ring: circumference; Mesh: sum of all conductors |
| Resistivity (ρ) | Soil's electrical resistivity | Measured in Ω·m; use field measurement or typical values |
| Safety Voltage (U₀) | Maximum permissible touch voltage | 50 V (dry), 25 V (wet/high-risk) |
A low grounding resistance ensures that during an earth fault, sufficient current flows to trip the protective device quickly. More importantly, it limits the touch voltage (V = I × R) to a safe level—typically ≤50 V in dry areas or ≤25 V in wet locations.
Soil resistivity (ρ) directly impacts grounding resistance. Rocky or sandy soils have high ρ (up to 10,000 Ω·m), leading to poor conductivity and high resistance. Clay or moist agricultural soils have low ρ (10–150 Ω·m), making them ideal for earthing.
You can: (1) increase electrode length or depth, (2) add more parallel rods, (3) use conductive backfill (e.g., bentonite), (4) install a ring or mesh network, or (5) treat the soil to reduce resistivity.
No. Due to mutual coupling, adding a second rod typically reduces resistance by only 30–40%, not 50%. The spacing between electrodes must be ≥ twice the rod length to achieve near-ideal parallel reduction.
Check that R ≤ U₀ / IΔn, where U₀ is the safety voltage (50 V or 25 V) and IΔn is the RCBO’s rated residual current (e.g., 0.03 A). For example, with a 30 mA RCBO and 50 V limit, R must be ≤ 1667 Ω—which is almost always satisfied. The real challenge is achieving low enough R for high-sensitivity or high-current systems.
To comply with IEC 60364-4-41, your grounding system must satisfy:
Where:
• R = Calculated grounding resistance (Ω)
• U₀ = Safety voltage (50 V or 25 V)
• IΔn = Rated residual operating current of the RCD/RCBO (e.g., 0.03 A for 30 mA)
Tip: Always validate critical installations with on-site soil resistivity measurements (e.g., Wenner four-point method) rather than relying solely on typical values.
