Available Fault Current Calculator

Calculate available fault current (Isc) from transformer kVA & %Z—or enter a known kA—then verify the panel SCCR / kAIC mark. Example: ~24 kA from 1000 kVA / 5%Z / 480 V vs 25 kA mark → adequate. Not FC2, feeder impedance, or arc-flash.

Quick Available Fault Current Calculator

Mode 1: estimate Isc from transformer (matches “fault current calculator” intent). Mode 2: direct SCCR vs known available kA.

Estimate from transformer kVA & %Z
Direct compare (available kA vs equipment SCCR)

Advanced screening inputs

Use the transformer path only when its kVA, secondary voltage, and nameplate impedance are known; otherwise compare the available utility fault-current value directly to the marked SCCR.

Transformer kVA

Impedance %ZTypical distribution transformers: 4–6%.

Secondary voltage (V)

Phase

Equipment assembly SCCR (kA)Use the marked assembly SCCR. A protective device interrupting rating (kAIC) is a separate check.

Planning margin (%)Optional buffer—0% for direct mark comparison.

About this calculator

Free available fault current screen (transformer kVA/%Z) plus SCCR / kAIC pass/fail—aligned to the same job as OEM fault-current tools, without feeder impedance or X/R. Hub: protection calculators. Definition: short-circuit current rating (SCCR). Next: breaker sizing.

Calculation Results

Available fault current: ~24.1 kA (1000 kVA · 5%Z · 480 V 3φ screen).

SCCR check: Adequate — 25 kA mark vs ~24.1 kA available.

Continue Your Calculation

After SCCR screening, size OCPD frames from load current in the breaker size calculator.

Breaker sizing →

Engineering disclaimer

Screening only—not a substitute for Eaton FC2-class point-to-point studies, UL 508A SB assembly calculations, or utility sign-off. Utility contribution, motor contribution, X/R, and series ratings are not modeled—confirm with a qualified engineer and manufacturer data.

Transformer available fault current chart (480 V, 5%Z screen)

Quick Isc ≈ IFL ÷ (%Z/100) at the secondary—utility and motor contribution not included. Use the calculator for other voltages or %Z.

Transformer kVA	IFL (A)	Available Isc (kA)	Typical SCCR mark to clear
500	≈601	≈12.0	14 / 18 kA+
750	≈902	≈18.0	22 / 25 kA+
1000	≈1203	≈24.1	25 / 35 kA+
1500	≈1804	≈36.1	42 / 65 kA+
2000	≈2406	≈48.1	65 kA+

How to calculate available fault current & check SCCR

Available fault current (transformer screen): IFL = kVA × 1000 ÷ (√3 × V) for 3-phase; Isc ≈ IFL ÷ (%Z ÷ 100)

SCCR check: Equipment SCCR (kA) ≥ available fault current (kA). The optional margin creates a separate planning target; it does not redefine the direct SCCR comparison.

Vs OEM tools (e.g. FC2): those add feeder length, conductor size, and labeling helpers. This page is a fast Isc + mark compare for planning—not a substitute for a signed study.

Definition: short-circuit current rating (SCCR) · Planning: Short-circuit planning · Coordination & SCCR

Common SCCR / kAIC marks (reference)

Mark (kA)	Typical context
10 / 14	Small panels, remote branches
18 / 22 / 25	Industrial MCC / panelboards
35 / 42 / 47	Higher fault industrial buses
65 / 85 / 100	Large switchgear, close-in utility

Worked example: 1000 kVA, 5%Z, 480 V → ≈24.1 kA available → a 22 kA panel fails the screen; pick 25 kA+. Direct: utility 18 kA vs 22 kAIC → adequate.

Frequently Asked Questions

How do you calculate available fault current?

Isc ≈ IFL ÷ (%Z/100). For 3-phase, IFL = kVA×1000÷(√3×V). Example: 1000 kVA, 5%Z, 480 V → ≈24.1 kA at the secondary. Utility and motor contribution add on top—this is a planning screen only.

How to calculate the SCCR rating?

Assembly SCCR comes from listing methods (e.g. UL 508A SB) or manufacturer combination tables—not from this calculator. Enter the marked kA value and compare it to available fault current.

Is SCCR the same as fault current?

No. Available fault current is system duty. SCCR is the equipment withstand mark. You need SCCR ≥ available fault current—see SCCR vs available fault current.

What is the SCCR value?

The nameplate or listing mark in kA (commonly 10–100 kA buckets). It is the maximum prospective fault current the assembly is rated to withstand.

What is SCCR vs kAIC?

SCCR is usually an assembly withstand rating; kAIC is typically a device interrupting rating. Read short-circuit current rating (SCCR) for NEC context.

Is this the same as Eaton FC2 or a full short-circuit study?

No—no feeder impedance, X/R, or NEC 110.24 label export. Use FC2-class or PE studies for signed deliverables; use this page for a fast Isc + mark check.

What is the next step after this SCCR check?

Size breakers, validate cable ampacity, then coordination & SCCR planning.