Short-Circuit Current Calculator

Estimate short-circuit current using source voltage and total path resistance (source + wiring + connections). Includes unit conversions and Show Work.

How to Use

  1. Enter the source voltage.
  2. Enter total path resistance (or build it from parts below).
  3. Read short-circuit current and estimated power dissipation.
  4. Open “Show Work” for formulas and steps in base units.
Short-Circuit Lab View
Visual feedback: higher current = faster flow; higher power = more heat.
V
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Rtotal
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Isc
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P
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Risk: —
Source V Path R (total) R Drag: V handle or R handle for quick “what-if” testing Solve V Solve R Solve I Results assume a DC source and purely resistive path (no inductive surge modeling).
Inputs & Settings
Enter voltage + resistance to compute short-circuit current. Build resistance from parts if desired.
Common: 5V, 12V, 14.4V, 24V, 48V
Includes source internal + wiring + contacts + fuses. Never use 0Ω.
Resistance Builder (optional)

Add up path pieces. The tool will sum these into Rtotal when “Use builder” is enabled.

Battery internal resistance or supply limit equivalent.
Positive + negative run combined (loop).
Lugs, crimps, terminals, switch contacts.
Optional; can be small but not zero.
Show Work (step-by-step)
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Work is shown in base units (V, Ω, A, W) for clarity and consistency.

Reference Formulas

Core relationship: I = V ÷ R (using total path resistance).

  • Short-circuit current: Isc = V ÷ Rtotal
  • Power dissipated in path: P = V × I = I² × R = V² ÷ R
  • Total path resistance: Rtotal = Rsource + Rwire + Rcontacts + Rfuse + …
This tool is an estimate for resistive paths (DC steady-state). It does not model AC fault current, inductive surge, or breaker time-current curves.

FAQ

Why is short-circuit current not “infinite”?

Real sources and wiring have resistance. Even a battery has internal resistance, and cables/contacts add more.

What should I use for resistance?

Use the best estimate you have for the complete loop (source + both conductors + contact points). Milliohms matter a lot.

Is this a fuse sizing tool?

No. It’s an electrical estimate. Fuse sizing depends on time-current curves, ambient temp, and conductor ratings.

Tool Info

Last updated:

Updates may include UI improvements, unit support, and calculation edge-case handling.