Electrical
Fault Current Calculator
Calculate available fault current at the end of a conductor run using the point-to-point method. Supports copper and aluminum, single- or three-phase systems.
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Calculations use the point-to-point method with NEC Chapter 9 Tables 8 & 9 conductor properties at 75°C. Source impedance is split using an assumed utility X/R ratio of 4.
Fault current at end of run
8,615
AReduced from 22,000 A at the source
About this calculator
NEC-compliant. Free to use. No watermarks.
Every panel and overcurrent device has an interrupting rating: the maximum fault current it can safely interrupt. NEC 110.9 requires every device to be rated for the fault current available at the point it's installed. NEC 110.24 requires that available fault current be marked on service equipment.
The point-to-point method uses the utility's available fault current at the source, then de-rates it through each conductor run based on length, wire size, and conductor material. This calculator runs that math and gives you a defensible number for the equipment label and the AHJ submittal.
NEC references
- NEC Article 110.9: Interrupting Rating
- NEC Article 110.10: Circuit Impedance, Short-Circuit Current Ratings
- NEC Article 110.24: Available Fault Current
- NEC Chapter 9, Tables 8 & 9: Conductor Properties
The same calculations, running live as you design.
Solar Design Lab runs this calculator (and a dozen more) live as you build plansets. Stamping from $150 per planset.