PROTECTION · CALCULATOR

Minimum short-circuit current

Free minimum short-circuit current: get minimum fault current estimate from line-to-ground voltage and verified minimum voltage factor. With the formula shown.

Written by Chameera Sampath · Not yet reviewed by a licensed electrician. See the methodology.

US (NEC) only · NFPA 70 / NEC — locally adopted editionDefaults are US values. Verify the locally adopted NEC edition and project data.Official reference ↗

Project inputs

Measurements

Line-to-ground voltage

Verified minimum voltage factor

Maximum hot fault loop impedance

Updates as inputs change. Unit changes preserve the same physical values.

THE MATH BEHIND THE ANSWER

Method & assumptions

Imin = cmin × U0 / Zloop,max

Requires verified hot impedance and voltage factor; not a complete disconnection assessment.

Results do not check every aspect of an electrical installation. The calculators follow US (NEC) practice only; a regional preset changes defaults such as voltage and units, and no result certifies NEC compliance.

Sources and validation →

Worked example

Line-to-ground voltage: 120 V · Verified minimum voltage factor: 0.95 · Maximum hot fault loop impedance: 1 Ω

Minimum fault current estimate: 114 A

This example uses the stated inputs; results for the entered values appear above.

Explore the protection branch →See the related electrical concepts →

Estimating and invoicing tool

Ampxa is developing an estimating and invoicing application for electrical contractors. The list below receives notice when it opens.