Earth electrode resistance calculator
Estimate an Australian earth electrode resistance record from entered soil resistivity, electrode geometry, count and user-entered efficiency factor.
single_rod_resistance = rho / (2 x pi x L) x (ln(8 x L / d) - 1); estimated_resistance = single_rod_resistance / (electrode_count x parallel_efficiency_factor); reported_resistance = measured_resistance if entered otherwise estimated_resistance; target_margin = target_resistance - reported_resistance- Soil resistivity, electrode dimensions, electrode count, parallel efficiency factor and target resistance are entered by the user.
- Measured resistance is optional and becomes the reported value when entered.
- Parallel factor is a user-entered project assumption, not a published spacing table.
- Keep the soil source, measurement record and target basis with the worksheet.
| Variable | Meaning | Unit | Use |
|---|---|---|---|
| rho | Soil resistivity | ohm m | Value entered from project soil data or documented assumption. |
| L | Electrode length | m | Driven or effective electrode length used by the worksheet. |
| d | Electrode diameter | m | Electrode diameter converted from millimetres. |
| electrode_count | Electrode count | count | Number of electrodes included in the entered method. |
| parallel_efficiency_factor | Parallel efficiency factor | factor | User-entered factor for the electrode group. |
| measured_resistance | Measured resistance | ohm | Optional field value from a traceable measurement record. |
| target_resistance | Entered target | ohm | Project or reviewer basis used for comparison. |
| target_margin | Target margin | ohm | Entered target minus reported resistance. |
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Earth electrode resistance calculator technical guide
Estimate an Australian earth electrode resistance record from entered soil resistivity, electrode geometry, count and optional measured value.
Earth electrode resistance calculator technical guide
Use this calculator when an Australian earthing record needs a transparent resistance estimate from entered soil resistivity, electrode geometry and a target value. The worksheet is useful for keeping a preliminary method, optional measured resistance and project target in one exportable record.
The calculator does not reproduce controlled earthing tables, soil models, field procedures or final design rules. It keeps the arithmetic visible so the project source documents and competent-person review can remain separate from the public worksheet.
| Record question | Calculator treatment | Outside the calculator |
|---|---|---|
| What method is being used? | Choose single electrode or parallel electrodes with entered factor. | Detailed earthing system design method. |
| What soil value applies? | Enter soil resistivity in ohm m. | Soil testing plan, seasonal variation and site interpretation. |
| What geometry is assumed? | Enter length, diameter and electrode count. | Installation method, spacing, connection details and product constraints. |
| What value is reported? | Use measured resistance if entered, otherwise use the estimate. | Field record quality and project review. |
User-entered method boundary
The single electrode estimate uses the relationship single_rod_resistance = rho / (2 x pi x L) x (ln(8 x L / d) - 1). The result depends heavily on the entered soil resistivity and geometry, so the worksheet should travel with the source of those values.
Parallel electrode records use a user-entered efficiency factor. This keeps the page from publishing spacing tables or hidden assumptions. If the project method uses a different model, enter only the values that match that method and keep the method source with the export.
| Field | Strong record | Weak record |
|---|---|---|
| Soil resistivity | Value tied to project soil data or documented assumption. | Generic soil value with no source. |
| Geometry | Length, diameter, count and method all visible. | A resistance number with no electrode details. |
| Parallel factor | Entered factor tied to project method. | Factor copied without spacing or method basis. |
| Measured value | Instrument record and date retained. | Measurement pasted without source context. |
| Target value | Project, reviewer or authority basis recorded. | Target number with no source. |
Worked Australian examples
A single electrode record uses 100 ohm m soil resistivity, 2.4 m length and 16 mm diameter. The worksheet estimates about 40.386 ohm. Against an entered 50 ohm target, the margin is about 9.614 ohm.
A parallel electrode record with three electrodes and a 0.65 entered efficiency factor estimates about 20.711 ohm. Against an entered 20 ohm target, the row remains a review item because the reported value is above the entered basis.
If a measured 62 ohm value is entered for the same single electrode assumptions, the measured value becomes the reported value. The estimate stays visible only as a comparison reference, and the measurement record should stay with the worksheet.
Review workflow
Use the project record as the starting point rather than the formula. The useful output is a traceable row: reference, method, soil source, geometry, estimated value, optional measured value, target and review note.
- Name the electrode group, switchboard, asset or project row.
- Enter soil resistivity and electrode geometry from the project basis.
- Choose single electrode or parallel electrodes with a user-entered factor.
- Enter the project target and optional measured resistance.
- Export the row with the soil source, measurement record and target basis.
| Result state | What it means | Practical next action |
|---|---|---|
| Estimate below entered target | The reported estimate is below the user-entered basis. | Keep the source record and target basis with the worksheet. |
| Estimate above entered target | The reported estimate is above the user-entered basis. | Review method, soil source, geometry and target before relying on the row. |
| Measured value entered | The measured value is used as the reported resistance. | Keep the instrument record and measurement context with the worksheet. |
| Source missing | The row cannot be traced. | Return to the project file before treating the number as a useful record. |
Boundary With Other Protection Records
Earth electrode resistance is not the same as fault loop impedance, protective conductor area, prospective short-circuit current or RCD test results. Use the fault-loop impedance calculator when the task starts from loop impedance and voltage. Use the protective conductor check when the task is conductor area comparison. Use earthing and MEN terms when the task is terminology rather than arithmetic.
Keeping those tasks separate prevents one worksheet from pretending to answer every protection question. Keep each measurement or estimate model visible and exportable.
Australian Standards Context
Australian earthing records sit within current Wiring Rules context, local authority requirements, soil and site conditions, product instructions, field records and competent-person review. AS/NZS 3000 is named as context because earth electrode records sit inside that installation environment.
This page does not reproduce controlled tables, test procedures, legal thresholds or field design methods. The user enters the comparison target and keeps the source with the project record. State or territory requirements, workplace procedures, manufacturer instructions and competent-person review can override the worksheet basis.
Single electrode record
A preliminary earth electrode row uses entered soil resistivity, one 2.4 m electrode and a user-entered target.
- Record reference
- EER-MS-1
- Method
- single-rod
- Soil resistivity
- 100 ohm m
- Electrode length
- 2.4 m
- Electrode diameter
- 16 mm
- Electrode count
- 1
- Parallel factor
- 1
- Entered target
- 50 ohm
- Estimate single electrodeApply the entered soil and geometry values to get 40.386 ohm before reporting logic.
- Choose reported valueUse the estimated 40.386 ohm value as the reported record.
- Compare with entered target50 - 40.386 = 9.614 ohm.
Reported resistance is 40.386 ohm.
The estimate sits below the entered target, subject to the soil source, method and project target being appropriate for the record.
- Soil resistivity is entered from project data or a documented assumption.
- The single-electrode formula is a simplified worksheet relationship.
- The result is not a field measurement or final design decision.
Parallel electrodes
A parallel-electrode worksheet uses three electrodes and a user-entered efficiency factor to avoid publishing a spacing table.
- Record reference
- EER-PARALLEL
- Method
- parallel-rods-entered-factor
- Soil resistivity
- 100 ohm m
- Electrode length
- 2.4 m
- Electrode diameter
- 16 mm
- Electrode count
- 3
- Parallel factor
- 0.65
- Entered target
- 20 ohm
- Estimate single electrodeApply the entered soil and geometry values to get 20.711 ohm before reporting logic.
- Choose reported valueUse the estimated 20.711 ohm value as the reported record.
- Compare with entered target20 - 20.711 = -0.711 ohm.
Reported resistance is 20.711 ohm.
The reported estimate is above the entered target, so the row remains a review item until the method and project basis are checked.
- Parallel efficiency is entered by the user.
- Spacing, soil conditions and installation details remain outside the simplified worksheet.
- The target value source stays with the project record.
Measured review
A worksheet includes an optional measured value so the report can show both the estimate and the measurement basis.
- Record reference
- EER-MEASURED
- Method
- single-rod
- Soil resistivity
- 100 ohm m
- Electrode length
- 2.4 m
- Electrode diameter
- 16 mm
- Electrode count
- 1
- Parallel factor
- 1
- Entered target
- 50 ohm
- Estimate single electrodeApply the entered soil and geometry values to get 40.386 ohm before reporting logic.
- Choose reported valueUse the measured 62 ohm value as the reported record.
- Compare with entered target50 - 62 = -12 ohm.
Reported resistance is 62 ohm.
The measured value becomes the reported value and sits above the entered target, so the measurement record needs review.
- The measured value comes from a traceable field record.
- The estimate remains visible for comparison only.
- The instrument record and target source remain with the worksheet.