Admissible I2t Calculator for Cables – k2S2 for Copper and Aluminum Conductors
Calculate the maximum admissible let-through energy (I2t = k2S2) for copper or aluminum cables based on IEC 60364 standards. Ensure your protective devices can clear faults before cables overheat.
How It Works
This tool computes the highest I²t (in A²·s or kA²·s) a cable can safely withstand during a short circuit, using the formula:
Where:
S = conductor cross-sectional area (mm²)
k = material & insulation constant per IEC 60364-5-54
Input Parameters
- Conductor Type: Phase, single-core PE, or multi-core PE
- Wire Size: Cross-section in mm² (e.g., 2.5, 10, 95)
- Material: Copper (Cu) or Aluminum (Al)
- Insulation Type:
- Thermoplastic (PVC)
- Thermosetting (XLPE / EPR)
- Mineral-insulated (bare or PVC-covered, various conditions)
Output Results
- Admissible let-through energy (I²t) in kA²·s
- Reference to IEC 60364-4-43 & IEC 60364-5-54
- Guidance for comparing with protective device’s I²t rating
Frequently Asked Questions (FAQ)
What is admissible I2t for a cable?It’s the maximum fault energy (I²t) a cable can absorb during a short circuit without damaging its insulation or conductor—calculated as k²S² per IEC standards.
How is the k factor determined?The k value depends on conductor material (Cu/Al), insulation type, and initial/final temperatures. Standard values are defined in IEC 60364-5-54 Table 43A.
Why does insulation type affect I2t?Different insulations tolerate different final temperatures during a fault (e.g., PVC: 160°C, XLPE: 250°C). Higher temperature limits → higher k → greater I²t capacity.
Can I use this for DC systems?This calculator follows IEC AC standards. For DC, thermal withstand is similar, but verify protection coordination separately as DC arcs behave differently.
How do I check if my breaker is compatible?Compare the cable’s admissible I²t (from this tool) with the breaker’s actual let-through I²t (from its datasheet). The breaker’s I²t must be lower than the cable’s value.
Applications
- Cable Sizing Verification: Confirm selected cables meet thermal withstand requirements during short circuits.
- Protection Coordination: Ensure fuses or circuit breakers operate fast enough to protect conductors.
- Compliance with IEC 60364: Demonstrate adherence to international electrical installation standards.
- Design Review: Validate existing installations during upgrades or safety audits.
- Training & Education: Teach electrical safety principles using real-world I²t calculations.
Who Should Use This Tool?
- Electrical design engineers
- Project engineers in industrial & commercial buildings
- Electrical inspectors and safety auditors
- Contractors and installers working to IEC standards
- Students of electrical engineering or power systems
