Protective conductor adiabatic equation
The PE conductor must withstand fault energy until the protective device clears.
Smin = I × √t / kI²t ≤ k²S²where:
- S
- Protective conductor cross-section[mm²]
- I
- Earth fault current[A]
- t
- Clearing time[s]
- k
- Material and insulation thermal constant[A√s/mm²]
Mechanical minimums and fault-loop requirements are separate checks.
How to use the Protective Conductor Size Calculator
Calculate minimum protective-conductor cross-section using the IEC adiabatic equation and a user-selected material k value. Start by choosing the operating mode, then enter values from nameplates, measurements, or project documents in the units shown. The result updates immediately and keeps intermediate quantities visible for review.
- Confirm the system and calculation mode.
- Enter measured or manufacturer-rated values.
- Review the primary result and intermediate metrics.
- Continue with the related protection or equipment-selection checks.
Calculation method and validation
The equations and symbol definitions above show the complete calculation basis. Inputs are checked before calculation so zero, negative, incompatible, or physically impossible combinations are flagged instead of silently producing a misleading result.
How to interpret the result
Use the main result as a starting value and read every supporting metric. Fault current remains constant for the entered duration Entered k value matches conductor material, insulation, and temperature limits A passing or recommended result means the entered mathematical conditions are satisfied; it does not certify the complete installation or a particular product combination.
- Fault current remains constant for the entered duration
- Entered k value matches conductor material, insulation, and temperature limits
Selection limits and next checks
Preliminary engineering estimate only. Verify the final design against the current applicable standard, local rules, manufacturer data, and project conditions. Also check minimum mechanical cross-section, bonding requirements, terminals, and fault-loop impedance. Compare the output with the current applicable standard, local rules, exact VIOX product datasheet, environmental conditions, protection coordination, and the engineer's project requirements before procurement or installation.
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Assumptions
- Fault current remains constant for the entered duration
- Entered k value matches conductor material, insulation, and temperature limits
Important Warnings
- Preliminary engineering estimate only. Verify the final design against the current applicable standard, local rules, manufacturer data, and project conditions.
- Also check minimum mechanical cross-section, bonding requirements, terminals, and fault-loop impedance.