Cable short-circuit rating calculator
Check a cable or earth conductor against the prospective fault. Enter the fault current and clearing time to get the minimum conductor area, or a size to get its short-time withstand current, using the adiabatic equation and IEC k factors.
Basis
Adiabatic equation and k factors: IEC 60364-4-43 (Table 43A); see also IEC 60949.
Reference values for planning and comparison. Confirm against the current standard, the purchaser’s specification and the manufacturer’s datasheet before ordering.
One-second short-circuit rating (kA)
| Size | Copper, XLPE / EPR (k=143) | Copper, PVC (k=115) | Aluminium, XLPE / EPR (k=94) | Aluminium, PVC (k=76) |
|---|---|---|---|---|
| 16 mm² | 2.29 | 1.84 | 1.5 | 1.22 |
| 25 mm² | 3.58 | 2.88 | 2.35 | 1.9 |
| 35 mm² | 5.01 | 4.03 | 3.29 | 2.66 |
| 50 mm² | 7.15 | 5.75 | 4.7 | 3.8 |
| 70 mm² | 10.01 | 8.05 | 6.58 | 5.32 |
| 95 mm² | 13.59 | 10.93 | 8.93 | 7.22 |
| 120 mm² | 17.16 | 13.8 | 11.28 | 9.12 |
| 150 mm² | 21.45 | 17.25 | 14.1 | 11.4 |
| 185 mm² | 26.46 | 21.28 | 17.39 | 14.06 |
| 240 mm² | 34.32 | 27.6 | 22.56 | 18.24 |
| 300 mm² | 42.9 | 34.5 | 28.2 | 22.8 |
| 400 mm² | 57.2 | 46 | 37.6 | 30.4 |
| 500 mm² | 71.5 | 57.5 | 47 | 38 |
| 630 mm² | 90.09 | 72.45 | 59.22 | 47.88 |
Worked example: Minimum copper XLPE size for 25 kA for 1 s
- S = I √t ÷ k = 25,000 × √1 ÷ 143.
- S = 174.8 mm².
- Next standard size: 185 mm².
What is the k value for copper XLPE cable?
143 for copper conductors with XLPE or EPR insulation (90 °C to 250 °C); 94 for aluminium XLPE; 115 for copper PVC and 76 for aluminium PVC up to 300 mm².
What is the 1-second short-circuit rating of a 240 mm² copper XLPE cable?
I = k × S / √t = 143 × 240 / 1 ≈ 34.3 kA for one second. For 0.5 s it rises to about 48.5 kA.
Does the metallic screen need checking too?
Yes. In MV and HV cables the copper screen or metallic sheath carries earth-fault current and has its own rating. Specify the earth-fault current and duration in the enquiry.