Analyze fault current using practical network equipment inputs. Compare source, transformer, cable, and motor effects. Generate charts, exports, and clear, study-ready electrical results fast.
| Case | Voltage (kV) | Source level (MVA) | Transformer (kVA) | Impedance (%) | Cable length (m) | Total initial current (kA) | Peak current (kA) |
|---|---|---|---|---|---|---|---|
| LV panel | 0.415 | 250 | 1,500 | 6.00 | 35 | 24.678 | 47.426 |
| MCC bus | 0.480 | 350 | 2,500 | 5.75 | 20 | 40.340 | 84.500 |
| Remote load bus | 0.400 | 180 | 1,000 | 6.50 | 80 | 12.030 | 20.040 |
Zsource = V² / Ssc
Use system line voltage in kV and available short-circuit level in MVA. The result is the source Thevenin impedance in ohms at the studied bus.
Ztransformer = (Z% / 100) × (V² / Stransformer)
The transformer percent impedance is converted to ohms on the selected voltage base. This usually dominates low-voltage fault duty near transformer terminals.
Rcable = Rkm × Lkm
Xcable = Xkm × Lkm
|Zcable| = √(R² + X²)
Longer cables increase system impedance and reduce available short-circuit current at remote boards or motor control centers.
|Ztotal| = √((ΣR)² + (ΣX)²)
Isym = c × V / (√3 × |Ztotal|)
The voltage factor c lets you study conservative maximum duty. Current is reported in kA for practical equipment checks.
Imotor = multiplier × P / (√3 × V × pf × η)
Ipeak = k × √2 × Iinitial
This adds an initial motor contribution and estimates asymmetrical peak duty using the total system R/X relationship.
Use manufacturer data, utility fault data, and corrected conductor impedances whenever available. Final protection studies should still be checked against your project standard.
It estimates a three-phase bolted fault at the selected bus. That case is commonly used for maximum interrupting-duty checks because it usually produces the highest symmetrical current.
Longer cables add resistance and reactance. Higher impedance limits current flow, so remote panels usually see lower available fault current than buses close to the transformer.
Transformer percent impedance often dominates low-voltage short-circuit calculations. A lower impedance transformer usually delivers higher fault duty on its secondary side.
The X/R ratio affects the DC offset and the asymmetrical peak current. Higher X/R systems generally produce larger peak duty on switching and protective devices.
Yes, when large motors are running near the faulted bus. Rotating machines can feed current back into the fault for the first few cycles.
It adjusts the prefault voltage for a conservative maximum-duty estimate. Many studies use a factor slightly above nominal voltage for worst-case screening.
It is useful for early screening and design checks. Final breaker selection should also consider applicable standards, device curves, and detailed coordination studies.
No. It gives a practical engineering estimate, but formal studies should include exact impedances, utility data, sequence networks, and project-specific assumptions.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.