Available Fault Current Estimator

How It Works

1. Enter Source Data

   Choose transformer mode with kVA, secondary voltage, phase, and percent impedance, or utility mode with a dated available-fault-current value.

2. Add Conductor Hops

   Enter feeder conductor size, material, length, and parallel sets. The app applies a resistance-only point-to-point reduction.

3. Review Source Fault Current

   See the source-terminal screen before downstream conductor resistance is applied. Transformer mode assumes an infinite primary bus unless you use utility data.

4. Review Downstream AFC

   Compare the final available fault current against common AIC rating screens while keeping the app limitations visible.

5. Verify Before Use

   Check utility data, transformer nameplate impedance, X/R, motor or generator contribution, equipment markings, series ratings, adopted code, and AHJ requirements before labels or equipment decisions.

Built For

• Electricians doing a first-pass available fault current screen before requesting formal data
• Electrical engineers sanity-checking transformer and feeder assumptions before a study
• Inspectors and plan reviewers discussing why dated AFC values and equipment markings matter
• Electrical contractors comparing common AIC rating screens during early equipment planning
• Plant electricians evaluating how transformer or feeder changes can affect available fault current
• Estimators flagging when a project needs formal short-circuit and SCCR review

Features & Capabilities

Point-to-Point Screen

Uses a simplified transformer or entered-utility source value and downstream conductor resistance hops. It is not a complete IEEE short-circuit study.

Transformer Source Estimate

Calculates transformer source fault current from kVA, secondary voltage, phase, and percent impedance for preliminary screening.

Conductor Resistance Hops

Shows how entered feeder length, size, material, and parallel sets reduce the local resistance-only available-fault-current screen.

Common AIC Rating Flags

Compares the calculated screen against common kAIC ratings and warns that listed device, equipment, voltage, SCCR, and series-rating data still control.

Single-Phase and Three-Phase

Handles both system configurations for the local source and conductor-resistance screen.

PDF Export

Export the screening inputs, assumptions, warnings, and source pointers for internal review records.

Assumptions

• Transformer mode assumes infinite primary bus unless separate utility or study data is entered
• Point-to-point reduction is resistance-only and uses the app local conductor table
• Transformer impedance uses the entered %Z or a local kVA-range default; tolerance is not applied automatically
• Reactance, raceway effects, conductor temperature, and installed conductor geometry are not fully modeled
• Bolted fault screen only; arcing current and incident energy are not calculated
• Motor, generator, UPS, battery, and inverter contribution are not included

Limitations

• Does not perform asymmetrical fault current or X/R duty calculations
• Does not verify motor contribution, generator contribution, inverter contribution, or utility network changes
• Does not calculate arc flash incident energy, PPE, or approach boundaries
• Does not perform selective coordination or protective-device duty evaluation
• Does not verify UL listing, panelboard SCCR, classified breakers, or series-rated combinations
• Does not account for every busway, switch, fuse, breaker, splice, lug, raceway, or transformer tolerance in the real circuit

References

• Eaton Bussmann FC2 Available Fault Current Calculator source pointer
• IEEE 551 - Calculating AC Short-Circuit Currents in Industrial and Commercial Power Systems source pointer
• NFPA 70 National Electrical Code source pointer
• UL 489 Molded-Case Circuit Breakers source pointer
• UL Molded Case Circuit Breaker Marking and Application Guide
• OSHA 1910 Subpart S Electrical source pointer

Frequently Asked Questions