PROTECTION · CALCULATOR

Cable protection from short-circuit

Free cable protection from short-circuit: get cable withstand from conductor area, verified material/insulation k factor, fault current and disconnection time.

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

Conductor area

kcmil

Verified material/insulation k factor

A√s/mm²

Fault current

Disconnection time

Set area from AWG (geometric equivalent)

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

THE MATH BEHIND THE ANSWER

Method & assumptions

I²t ≤ k²S²; Smin = I√t / k

Adiabatic approximation for short durations. Enter k from adopted code/material data; protective let-through energy may require manufacturer curves.

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

Conductor area: 6.53 kcmil · Verified material/insulation k factor: 115 A√s/mm² · Fault current: 1,000 A · Disconnection time: 0.1 s

Cable withstand: 144,789.403 A²s · Fault energy: 100,000 A²s · Minimum adiabatic area: 5.427 kcmil

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

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