Short Circuit & Arc Flash Calculator

electrical

Calculates available short circuit current at a point downstream of a transformer (accounting for cable impedance and X/R ratio) and IEEE 1584-2018 arc flash incident energy for PPE selection.

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System Voltage

System line-to-line voltage in volts at the point of fault. Common values: 208, 240, 480, 600, 4160, 13800. If omitted, defaults to 480 V.

Transformer Kva*

Transformer nameplate kVA rating. Standard dry-type sizes: 15, 30, 45, 75, 112.5, 150, 225, 300, 500, 750, 1000, 1500, 2000, 2500. Standard dry-type: 75-2500 kVA. Standard liquid: 500-10000 kVA.

Transformer Impedance Pct*

Transformer nameplate impedance in percent (%Z). Found on the transformer nameplate. Typical values: 2-6% for dry-type, 4-8% for liquid-filled.

Transformer Xr Ratio

Transformer X/R ratio (reactance to resistance). Typical range: 3-8 for dry-type, 5-15 for liquid-filled. Higher X/R increases asymmetric fault current. If omitted, defaults to 4.5.

Cable Length Ft

One-way length of feeder cable in feet from transformer secondary to the point of fault. Longer cables reduce available fault current. Distance from transformer secondary to equipment. Typical: 10-200 ft. If omitted, defaults to 25 ft.

Cable Size Awg

Cable conductor size in AWG or kcmil notation. Valid sizes: 14-1 AWG, 1/0-4/0 AWG, 250-1000 kcmil. Example: '4/0 AWG', '500 kcmil'. If omitted, defaults to '500 kcmil'.

Equipment Class

Type of equipment enclosure at the fault location. Determines electrode gap and working distance per IEEE 1584-2018. If omitted, defaults to 'switchboard'.

Fault Clearing Time Cycles

Protective device clearing time in cycles (60 Hz basis). Includes relay sensing + breaker operating time. Common values: 6 (instantaneous), 30 (typical), 120 (delayed). If omitted, defaults to 30 cycles.

Upstream Fault Mva

Available fault MVA from the utility at the transformer primary. Obtain from the utility company. If provided, accounts for utility source impedance. If omitted, assumes infinite bus (conservative).

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Reference data

This calculator pulls live values from the following engineering reference tables in the database.

short circuit data
arc flash parameters

About this calculator

Short Circuit & Arc Flash Calculator is part of the Engineering Database calculator suite. Each tool runs deterministic calculations against authoritative reference data and code-compliant methods, so results are reproducible and traceable to source standards.

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Reference data

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