PROTECTION · CALCULATOR

Design current calculator

Free design current calculator: get design current from connected load, voltage, power factor and verified demand 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

Connected load

Voltage

Power factor

SupplyVerified demand factor

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

THE MATH BEHIND THE ANSWER

Method & assumptions

Ib = P × demand / (k × V × PF)

Demand factors are project-specific; no residential code load calculation is implied.

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

Connected load: 12 kW · Voltage: 120 V · Power factor: 0.85 · Supply: Single phase · Verified demand factor: 1

Design current: 117.647 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.