Running short-circuit analysis
This guide shows you how to run short-circuit analysis on your single-line diagram and interpret the results.
Before you start
Ensure your diagram has:
- At least one power source (utility feed or generator)
- Complete network with all components connected
- Utility feed short-circuit MVA and X/R ratio specified
- Generator subtransient reactance (X''d) if applicable
- Transformer impedance percentages
- All component voltage ratings
Missing source impedance data causes analysis to fail.
Running the analysis
- Open your project in the SLD editor.
- Verify all sources have impedance data.
- Click Run Short-Circuit button in the toolbar.
- EKX runs the validated three-phase maximum-current short-circuit calculation.
- Analysis executes in 2-5 seconds.
- Results appear on the single-line diagram.
Selecting fault type
Three-phase fault (recommended for equipment rating):
- Highest fault current
- Use for breaker interrupting capacity
- Most conservative
The current production workflow supports three-phase maximum-current analysis only. Phase-to-phase, single-phase, minimum-current, and all-fault-type workflows require separate validation before they are enabled.
Viewing results
Results display shows:
Per bus:
- Fault current magnitude (kA)
- Peak fault current (kA)
- Fault MVA
- Voltage during fault
Critical buses:
- Highest fault currents highlighted
- Identifies locations needing high interrupting capacity
Summary:
- Maximum, minimum, average fault currents
- System fault level
Interpreting fault currents
High fault currents (>20 kA at 480V):
- Near utility connection or large generators
- Require high interrupting capacity breakers (65kA, 100kA AIC)
- May need current-limiting fuses
- Higher arc flash hazard
Medium fault currents (10-20 kA):
- Middle of distribution system
- Standard industrial breakers (25kA, 42kA AIC)
- Typical for most equipment
Low fault currents (<10 kA):
- End of long feeders
- Far from sources
- Lower interrupting capacity acceptable
- Verify protection sensitivity
Compare fault currents to breaker interrupting capacity ratings. Breaker AIC must exceed fault current at installation point.
Equipment verification
Circuit breakers:
- Interrupting capacity ≥ fault current
- Example: 20 kA fault requires ≥22 kA AIC breaker
- Use next standard size up for safety margin
Buses and switchgear:
- Short-circuit withstand rating
- Based on peak current and duration
- Verify bracing adequate
Cables:
- Short-circuit withstand: I²t rating
- Duration typically 0.1-1.0 seconds
- Larger cables have higher withstand
Coordination verification
Short-circuit results used for protection coordination:
- Plot device time-current curves.
- Mark fault currents on the plot.
- Verify upstream device is slower than downstream at fault current.
- Maintain separation for selectivity.
ekx may support coordination plotting in future versions.
Arc flash considerations
Fault currents determine arc flash incident energy:
Higher fault current:
- Higher incident energy
- Greater arc flash hazard
- More extensive PPE required
- Larger arc flash boundary
Lower fault current:
- Lower incident energy
- Reduced hazard
- Less PPE needed
Arc flash analysis is planned for a future release and will use short-circuit results as input. This feature is not yet available.
Troubleshooting failed analysis
"No sources defined":
- Add utility feed or generator
- Verify source has impedance data
"Missing transformer impedance":
- Set transformer Z% in properties
- Use typical value if nameplate unavailable
"Network not connected":
- Check for isolated components
- Ensure all buses connect to main system
"Calculation did not converge":
- Verify all impedances are positive, non-zero
- Check for missing component data
- Review validation warnings
Exporting results
Export short-circuit data for reporting:
- Click Export Results button.
- Results save to
debug-exports/sc-debug-[timestamp].md. - File contains fault currents for all buses.
- Include in project documentation.
Related topics
- Understanding short-circuit - Short-circuit fundamentals
- Fault types - Different fault scenarios
- Protection devices - Breaker sizing based on fault currents