This simulator shows why a low-impedance fault produces very large current and why distance matters to anyone working near it. A source transformer feeds a bus; you set its size and impedance, add cable resistance, and choose how far away a worker stands. The lab reports the bolted three-phase fault current, an estimated arc current, a simplified incident energy and the NFPA 70E-style PPE category it falls into.
• A schematic with a transformer block (kVA and percent impedance), a bus, a glowing arc that changes color with the PPE category, and a worker figure at the chosen distance. • Five sliders: system voltage, transformer kVA, transformer impedance, cable resistance and working distance. • Readout tiles for ISC (3-phase), arc current, incident energy in calories per square centimetre and PPE category. • A color-coded PPE requirement banner that runs from Cat 0 to Cat 4, with notes, formulas and a worked example below the controls.
A transformer can only push so much current into a bolted secondary fault. Full-load current is the kVA rating divided by the voltage times √3; dividing 100 by the percent impedance gives the multiple of full-load current that flows into a zero-impedance fault. A 500 kVA, 480 V unit at 5 percent impedance has about 601 A of full-load current and roughly 12 kA of bolted fault current. Cable resistance between the transformer and the fault adds series impedance and lowers the current.
An arcing fault carries less current than a bolted one because the arc has its own impedance; the simulator takes arc current as 85 percent of the bolted value. Incident energy in this teaching model rises with arc current and falls with the square of working distance, which is why small changes in distance matter so much. The result is grouped into PPE categories 0 through 4 using energy bands. It is a simplified estimate for learning, not a substitute for an IEEE 1584 arc-flash study.
The transformer's kVA rating, voltage and percent impedance. Full-load current times 100 divided by the percent impedance gives the bolted three-phase fault current at the secondary terminals. Lower impedance or a larger kVA rating means a higher available fault current.
A bolted fault is a theoretical zero-impedance connection. A real arcing fault includes the arc itself as an impedance in the circuit, so less current flows. This simulator uses a fixed 85 percent factor for that reduction.
Thermal energy from an arc spreads outward, so the energy reaching a person falls roughly with the square of distance. In this teaching model incident energy is proportional to arc current and inversely proportional to distance squared, so doubling the distance cuts the reading to about a quarter.
No. It is a simplified educational model. A real arc-flash assessment follows IEEE 1584 or an equivalent method and accounts for clearing time, electrode configuration, enclosure size, gap and other factors. Use an engineering study for equipment labels and PPE decisions.