Fault types

Short-circuit studies use different fault types depending on the engineering question. Each type produces different fault currents and affects equipment differently.

EKX's current production calculation path supports validated three-phase maximum-current analysis only. The other fault types below are engineering background and planned validation scope, not currently enabled production workflows.

Three-phase fault (3ph)

Most severe fault:

• All three phases short-circuited together
• Highest fault current magnitude
• Balanced fault (symmetrical on all phases)
• Used for equipment rating verification

When to use:

• Breaker interrupting capacity sizing
• Bus bracing calculations
• Equipment worst-case rating
• Most conservative analysis

Typical magnitude:

• Highest fault current at any location
• 1.0 per-unit base for comparison
• Other fault types are lower

Phase-to-phase fault (2ph)

Two phases short-circuited:

• Lower current than three-phase fault
• Typically 87% of three-phase current
• Unbalanced fault
• One phase remains healthy

When to use:

• Coordination studies
• Protection device settings
• Realistic fault scenarios
• Delta-connected systems

Typical magnitude:

• About 0.87 × three-phase fault current
• Varies by system grounding and configuration

Single-phase fault (1ph)

One phase to ground:

• Common in grounded systems
• Current magnitude depends on grounding method
• Can be higher or lower than three-phase fault
• System grounding critical

Grounding effects:

Solidly grounded systems:

• Single-phase fault ≈ three-phase fault
• Low zero-sequence impedance
• High ground fault current

Resistance grounded:

• Lower ground fault current
• Intentionally limited for safety
• Common in medium voltage systems

Ungrounded systems:

• Very low ground fault current
• First fault may continue operation
• Uncommon in modern practice

When to use:

• Ground fault protection settings
• Grounding system design
• Single-phase equipment protection
• Realistic fault analysis

Phase-to-phase-earth fault (2ph-e)

Two phases to ground:

• Higher than phase-to-phase fault
• Lower than three-phase fault typically
• Unbalanced fault
• Depends on grounding impedance

When to use:

• Complete fault analysis
• Grounded systems only
• Worst-case unbalanced fault

Fault current comparison

Typical relative magnitudes (solidly grounded system):

Actual values vary by system grounding and impedance.

Selecting fault type

For equipment ratings:

• Use three-phase fault
• Most conservative
• Required for breaker selection

For protection coordination:

• Calculate all fault types
• Verify protection operates correctly for all scenarios
• Minimum fault current determines sensitivity

For arc flash analysis:

• Use three-phase fault
• Highest incident energy
• Worst-case personnel protection

For comprehensive study:

• Run all fault types
• Identify limiting cases
• Verify grounding effectiveness

In EKX today, use the three-phase maximum-current result for equipment interrupting-capacity and withstand checks. Do not treat phase-to-phase, single-phase, phase-to-phase-earth, or minimum-current cases as available until the app exposes them with their own tested calculation fixtures.

System grounding influence

Solidly grounded (most common in US):

• Neutral connected directly to ground
• High ground fault current
• Single-phase fault ≈ three-phase fault
• Typical for 480V and below

Resistance grounded:

• Neutral through resistor to ground
• Limited ground fault current (5-10A typical)
• Reduces arc flash hazard
• Common in medium voltage (5-15kV)

Ungrounded:

• Neutral isolated from ground
• Very low ground fault current
• Can operate through first fault
• Rare, special applications only

Grounding method dramatically affects single-phase fault currents.

When to use each type

Routine analysis:

• Three-phase fault only
• Fastest calculation
• Covers worst case

Detailed coordination:

• Three-phase and phase-to-phase
• Verifies protection for realistic faults
• Ensures minimum fault current detected

Complete analysis:

• All fault types
• Comprehensive protection verification
• Grounding system validation
• Required for critical systems

Related topics

• Understanding short-circuit - Short-circuit analysis fundamentals
• Running analysis - How to execute short-circuit calculations
• Protection devices - Interrupting capacity based on fault currents