Fault Current Calculator
Available fault current and short-circuit calculations using the point-to-point method. Model the service from transformer to panel and get a value at every point, in seconds, from your mobile, tablet, or desktop.
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How it works
Start at the source
Enter the AFC on the source branch from utility data or a meter reading, or calculate it from the transformer's kVA and %Z. Pick the service voltage and you're set.
Build the chain
Add each point in the chain, pick the equipment type, and name it if that helps. Editing is fast, so reworking a run or renaming a node takes seconds.
Clean PDF, ready to send
One click exports the full chain and per-point AFC in a branded PDF, with headers that match your load calcs and line diagrams. Ready to hand to a client or an inspector.
Built for the office and the field
Live recalculation
Every AFC value updates as you edit lengths, sizes, and sources.
Name every node
Label each point in the chain, meter, transformer, panel, so the report reads like your job.
Conductor data built in
Conductor C-values for every copper and aluminum size, applied automatically.
Start from anywhere
Seed the source with a known utility AFC, or calculate it from the transformer's kVA and %Z.
All common voltages
Residential and commercial services, single- and three-phase: 120/240V, 208Y/120V, 480Y/277V, 480V delta, and more.
Keep organized
Every calc is saved to a shared dashboard for you and your team, ready to edit or share alongside your load calcs.
Clearly shows each point in the chain, not just a number
Every report prints the per-point AFC table with the method and assumptions. Use it to check equipment SCCR and interrupting ratings and to document available fault current for NEC 110.24 labeling. No side spreadsheet required.
Included in Commercial Pro
Fault current calculations come with Commercial Pro, alongside commercial load calcs, commercial panel schedules, and 3-phase voltages.
What is available fault current (AFC)?
Available fault current is the maximum current that can flow at a point in an electrical system during a bolted short circuit. Contractors document AFC to verify that equipment interrupting ratings are adequate, and NEC 110.24 requires service equipment to be field-marked with the maximum available fault current.
How does the calculator work?
It uses the point-to-point method. You model the system from the source (a known utility AFC, or a transformer's kVA and %Z) through wire runs, transformers, and panels, and the calculator gives you the available fault current at every point in the chain.
What assumptions does it make?
In calculate mode it seeds a worst-case infinite-bus source, and it uses conductor C-values for wire impedance. Every report prints its method and assumptions.
How is available fault current different from SCCR?
Available fault current (AFC) is how much current the system can deliver into a bolted short circuit at a given point. Short-circuit current rating (SCCR), and a breaker's interrupting rating (AIC), is how much fault current a piece of equipment can safely handle. Equipment SCCR/AIC needs to be at least the available fault current at that point (NEC 110.9). The calculator gives you the AFC so you can compare it against equipment ratings.
What voltages and phases does it support?
It handles common residential and commercial services, single- and three-phase, including 120/240V, 208Y/120V, 240V delta, 240/120V high-leg delta, 480Y/277V, 480V delta, and 600V. You pick the service voltage for the source and for any downstream transformer.
Which plan includes the fault current calculator?
Fault current calculations are included in the Commercial Pro plan, alongside commercial load calcs, commercial panel schedules, and 3-phase voltage options. See our pricing page for details.
Can I include fault current calculations in my project documents?
Yes. Like every Kopperfield document, fault current calculations support your business branding, sharing, and combined PDF packages together with load calculations, single line diagrams, and panel schedules.
Who can I contact with questions?
Send an email to team@kopperfield.com and we can help with questions about the fault current calculator or your subscription.
Complete your fault current calculations in seconds
Load calcs, line diagrams, panel schedules, and fault current, all on Kopperfield.
