Protection & Control calculator
Grounding Conductor Sizing: Thermal Area & Tape
Calculate minimum grounding-conductor thermal area and tape thickness from fault current, clearing time and a verified material k factor.
ProtectionBasis: Adiabatic thermal withstand only
Results
- Enter values to calculate
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How to use this calculator
Grounding conductor sizing has a thermal part and a grounding-system part. This tool checks whether a conductor has enough metal to absorb short-duration fault heating under an adiabatic assumption. Use the current that actually passes through that conductor after current division, not automatically the total station fault current.
Select k from the governing material and temperature assumptions. A buried substation grid also needs touch and step potential assessment, ground-potential rise, corrosion allowance, connection checks and mechanical minimums. In US work, distinguish substation grid design from NEC equipment-grounding and grounding-electrode conductor selection.
Formula
Amin = I √t / k; I²t ≤ k²A²; tape thicknessmin = Amin / width
I is RMS current in A through the particular conductor; t is seconds; A is mm²; k is A√s/mm² and depends on conductor material and permitted initial/final temperatures. For changing current, use the applicable equivalent energy integral: Amin = √(∫i²dt) / k.
Worked example
For an illustrative I = 10,000 A, t = 1 s and assumed k = 143 A√s/mm², Amin = 69.93 mm². A 25 mm-wide tape requires at least 2.80 mm thickness for this thermal calculation. A 25 × 3 mm tape has 75 mm²; it passes this single assumed thermal check.
Assumptions and standards
- Short-duration adiabatic check, t ≤ 5 s. Not a complete EN 50522 or IEEE 80 grounding design.
- Material k, initial temperature and permitted final temperature must be established for the project. Soil resistivity does not determine this k factor.
- For current-limiting protection, use verified device let-through I²t where applicable. Connections may impose a lower temperature limit.
Calculation model checked: November 4, 2026
Frequently asked questions
Is thermal area enough to design a substation ground grid?
No. A thermally adequate conductor can still be part of an unsafe grounding system. Touch/step voltage, ground-potential rise and the entire current-return network require separate checks.
Can I use one k value for copper and aluminium?
No. The factor depends on material and temperature limits, and must match the conductor and installation being assessed.
Can I use these results for final design?
Use them for preliminary design and checking. Final designs must be verified by a qualified engineer against the code edition and standards adopted where the work is installed.
Is my data sent anywhere?
No. Every calculation runs in your browser. Nothing you type is uploaded or stored on our servers.
References and further reading
Power system calculations: formulas and model guide