A cable can only be short-circuited. k²·S² ≥ I²·t It withstands (TS EN 60364-4-43); permissible opening time t_max = (k·S/I)². For example, a 25 mm² copper-XLPE (k=143) cable withstands 6 kA for 0.2 s (t_max ≈ 0.36 s).
k²·S² ≥ I²·t · t_max = (k·S / I)²
Example calculation: 25 mm² copper-XLPE (k=143), Ik=6 kA, t=0.2 s → t_max = (143×25/6000)² ≈ 0.36 s > 0.2 s → cable withstands.
Cable Short Circuit Withstand (I²t)
Check whether a cable can thermally withstand a potential short-circuit current and tripping time.
Allowed time
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Cable I²t strength
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Fault I²t
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Notes: The cable strength must be k²·S² ≥ I²·t (TS EN 60364-4-43). The allowable duration is t_max = (k·S/I)². The k value is for the phase conductor. (different from the protective conductor k). The adiabatic approach is valid for t ≤ 5 s; the protective tripping curve should also be evaluated.
How is it calculated?
- Select the cable cross-section (mm²) and the k value (conductor/insulation).
- Enter the short-circuit current (kA) and tripping time (s).
- Press Calculate; the endurance and allowed time will be displayed.
Frequently Asked Questions
How to check the short-circuit withstand capability of a cable?
With the condition k²·S² ≥ I²·t, the I²t allowed by the cable must be greater than the potential fault current and the protection tripping time.
What is the value of k?
For the phase conductor (TS EN 60364-4-43): copper-XLPE 143, copper-PVC 115, aluminum-XLPE 94, aluminum-PVC 76. It differs from the shielding conductor k.
When is the adiabatic equation valid?
For short-duration short circuits (t ≤ 5 s), the tripping curve of the protective device should also be evaluated.
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