Grounding Resistance Chart

Use this worksheet after the calculator result to record soil resistivity, rod dimensions, spacing, estimated or measured ohms, target basis, and field verification.

Open calculator

Quick reference table

A grounding resistance chart is a calculator-led planning worksheet. It keeps estimated rod resistance, field-test resistance, target notes, and electrode spacing context together before owner, utility, or AHJ review.

Grounding resistance worksheet

Grounding resistance worksheet
Field	Record from result	Follow-up
Electrode layout	Rod count, length, diameter, spacing	Confirm installed geometry
Soil basis	Measured or assumed resistivity	Document season and moisture conditions
Resistance value	Estimated or measured ohms	Compare with project target
Test method	Fall-of-potential or accepted method note	Attach instrument and setup notes
Review path	Owner, utility, or AHJ note	Close before using as final record

Grounding test context worksheet

Grounding test context worksheet
Context item	Record on worksheet	Why it matters later
Probe setup	Probe spacing, direction, and obstructions	Fall-of-potential readings depend on setup geometry
Season and moisture	Date, weather, soil condition	Resistance can move with soil moisture and temperature
Nearby metal	Fences, buried piping, rebar, utilities	Parallel paths can distort field readings
Target basis	Owner, utility, project, or code-screening note	The acceptance target must be tied to its source

Formula basis

Grounding record = electrode geometry + soil assumption + estimated or measured resistance + target basis + field-test method.

Electrode geometry includes rod length, diameter, quantity, spacing, and connection path.
Soil assumption is measured or estimated resistivity used for planning.
Measured resistance is the field-test result in ohms.
Target basis identifies whether the value is a project target, utility requirement, or code screening item.

Worked examples

Multi-rod grounding recordRecord rod quantity, spacing, soil assumption, estimated array resistance, measured field result, test method, and project target before documenting acceptance.

Seasonal retest comparisonKeep spring and dry-season readings beside probe layout, instrument model, soil notes, and electrode geometry so the owner can compare trends.

Assumptions. Balanced load and line-to-line voltage assumptions behind this chart.

Planning estimates can differ from field measurements because soil layers, moisture, seasonal conditions, and nearby electrodes affect resistance.
A resistance target alone does not prove bonding, equipment grounding, fault-clearing performance, or lightning protection adequacy.

Code and standard notes. Planning limits that should be checked before final equipment selection.

Use this chart as a field record; verify adopted NEC grounding electrode rules, utility or owner targets, IEEE grounding practices, test instrument setup, equipment manufacturer instructions, AHJ expectations, and qualified-person review before acceptance.

How to use this chart

1Separate estimate from testMark whether the ohm value came from the calculator model or from a field instrument.

2Record electrode contextWrite rod length, diameter, count, spacing, conductor path, and soil basis.

3Close acceptance notesDocument the project target, owner or utility requirement, test setup, and AHJ follow-up.

Worksheet checklist. Record source basis, review gaps, and assumptions before using the chart result.

Capture geometryRecord electrode count, length, spacing, material, and connection details.
Capture measurementDocument measured ohms, instrument, probe layout, soil condition, and date.
Capture target basisList the project target, code screening item, utility requirement, and reviewer.

Common mistakes to avoid. Review these before turning chart current into an equipment decision.

Treating an estimated rod value as an installed field-test result.
Using one resistance value as proof that bonding and fault-current paths have been verified.
Recording ohms without probe spacing, soil condition, instrument setup, or the target basis that makes the number meaningful.

Frequently asked questions

These answers explain how to use the chart without turning a quick reference into a final design decision.

Does a low resistance value prove the grounding system is complete?

No. Resistance-to-earth is one record. Bonding, electrode installation, conductor sizing, fault path, corrosion, and test method still need review.

Why record the test method?

Grounding measurements are sensitive to probe spacing, soil conditions, nearby metal, and instrument setup. The value needs context to be useful later.