Wiring and Protection
Short-Circuit Current Calculator
Calculate prospective fault current from source voltage and total fault impedance. The default values illustrate the workflow; replace them with measurements or ratings from one documented condition.
Calculate Prospective fault current
Use measurements from one operating condition.
Understanding the equation
For this worksheet, the governing relationship is Ifault = V ÷ Z. The participating entries are Source voltage and Total fault impedance.
For the example shown, prospective fault current equals 657.14 A. Treat that value as a demonstration, not a recommendation.
Calculate prospective fault current from source voltage and total fault impedance. Keep Fault Loop Impedance Calculator available for the companion calculation.
Interpreting the answer
Read Prospective fault current as the outcome of this equation, not as automatic equipment approval. Compare it with the applicable installation and equipment requirements.
A result without its source conditions is difficult to compare or audit. The ground potential rise step is handled by Grounding Voltage Rise Calculator.
Values this page needs
Record ambient temperature, bundling, insulation class, and termination conditions. Do not combine a worst-case value with unrelated nominal data.
Values used below a division bar must stay positive. Confirm decimal placement whenever a source uses a different unit scale. For the companion internal resistance calculation, open Battery Internal Resistance Calculator.
- Source voltage
- Default example: 230 V. Enter source voltage in V.
- Total fault impedance
- Default example: 0.35 Ω. Enter total fault impedance in Ω.
Practical limits
The protective device interrupting rating must exceed prospective current.
The arithmetic intentionally leaves out fault duration, protective-device curves, and conductor thermal limits. Resolve material omissions before selecting a standard size or rating.
Keep one-way and round-trip lengths clearly identified.
Documenting the calculation
Document source voltage and total fault impedance with prospective fault current. Keep enough context to reproduce the result later.
Carry prospective fault current as the raw numerical value until the final step. Apply standard sizes only after all checks are complete.
Common questions before using the result
Does the answer include a design margin?
No. Compare the value with the selected conductor and protective-device ratings and apply relevant equipment and installation requirements.
Why does Prospective fault current show several decimals?
Retain the raw result for comparison and create a separately rounded reporting value if needed.
Which input can create an undefined result?
A zero denominator is undefined, so the affected field has a positive minimum.
What data should go into Short-Circuit Current?
Use source voltage and total fault impedance from one operating condition. Use the installed route length, conductor material, and actual current path.