Disclaimer: RacewayIQ is an informational engineering tool only. All calculations must be independently verified by the user. Do not rely on these results as the sole basis for design, procurement, installation, construction, permitting, or code compliance decisions.

Motor Circuit Calculator

Check selected motor conductor ampacity, overload protection, and branch short-circuit / ground-fault protection using motor current, device type, and project assumptions. Motor circuits may require different current bases for conductors, overload protection, branch protection, disconnects, controllers, VFDs, and special applications.

Job Information

Project nameLocationPrepared byDateNotes

Main Inputs

Motor calculation modePreliminary sizing uses user-entered motor current and factors. Verify against adopted code, manufacturer data, and project requirements.Motor tag / equipment nameMotor typePhaseVoltageStarter / drive typeMotor current basisMotor conductor sizing, overload protection, and branch short-circuit / ground-fault protection may use different current bases. Verify which current basis applies to each part of the calculation.Motor current used for this check (A)Enter the code-table, nameplate, drive, manufacturer, or project-required current basis used for this calculation.Branch protection device typeSelect the protection type, then verify or enter the correct factor for the motor and device condition.Selected final conductor ampacity (A)Enter the final ampacity of the chosen conductor after all applicable adjustments.Selected overload protection setting (A)Use the overload relay, starter, or drive overload setting being checked.Selected branch short-circuit / ground-fault protection (A)Enter the selected breaker or fuse rating for branch short-circuit / ground-fault protection.

Advanced Inputs

Use these when the job has project-specific assumptions, manufacturer data, or review conditions.

Horsepower, optionalMotor nameplate FLA, optionalTable FLC, optionalService factor, optionalTemperature rise, optionalMotor conductor sizing factor

Common factor presets - verify before use.Motor overload factor

Common factor presets - verify before use.Branch short-circuit / ground-fault protection factor

Common factor presets - verify before use.

Result

Review

Overall status

Review Required

Minimum conductor ampacity

50 A

Selected final conductor ampacity

55 A

Conductor check

Pass

Maximum overload setting

46 A

Selected overload setting

46 A

Overload check

Review

Maximum branch protection

100 A

Selected branch protection

100 A

Branch protection check

Review

Reason

Selected values satisfy the entered factor-based checks, but overload and/or branch protection values are at their calculated maximums and require verification.

Practical Next Steps

Treat this as a workable planning result that still needs review.
Resolve warnings that are close to limits, based on manual assumptions, or missing manufacturer data.
Confirm the result against the project specification before procurement, permitting, or installation.

Verify whether code table full-load current, nameplate current, drive input current, or manufacturer data applies to each motor calculation.

Motor circuit factors were entered manually. Verify conductor, overload, and branch protection multipliers against the adopted code, motor type, protection type, and project requirements.

Selected overload setting is at the calculated maximum. Verify motor nameplate data, service factor, temperature rise, overload protection type, and applicable rules.

Selected branch protection is at the calculated maximum. Verify protection device type, exception rules, next-size provisions, and manufacturer requirements.

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Calculation Breakdown

Input Summary

Motor calculation mode: Check selected motor circuit
Motor tag / equipment name: Not entered
Motor type: General Single Motor
Phase: Three Phase
Voltage: 480 V
Horsepower: Not entered
Motor current basis: Code Table FLC
Motor current used for this check: 40 A
Branch protection device type: Inverse Time Breaker
Starter / drive type: Across The Line

Conductor Check

Motor conductor sizing factor: 1.25
Minimum conductor ampacity: 40 A x 1.25 = 50 A
Selected final conductor ampacity: 55 A
Result: Pass

Overload Protection Check

Motor overload factor: 1.15
Maximum overload setting: 40 A x 1.15 = 46 A
Selected overload setting: 46 A
Result: Review
Reason: Selected overload setting is at the calculated maximum.

Branch Short-Circuit / Ground-Fault Protection Check

Branch protection factor: 2.50
Maximum branch protection: 40 A x 2.50 = 100 A
Selected branch protection: 100 A
Result: Review
Reason: Selected branch protection is at the calculated maximum.

Design Review Reminders

Suggested disconnect review: Review Required
Controller / starter review: Review Required
VFD review: Not included
Grounding review: Not included / Review separately
Voltage drop review: Not included / Use Feeder or Voltage Drop Calculator

Overall Result

Status: Review Required
Reason: Selected values satisfy the entered factor-based checks, but overload and/or branch protection values are at their calculated maximums and require verification.

Code and Design References

NEC Article 430 and motor manufacturer data

Motor conductor, overload, short-circuit, ground-fault, controller, disconnect, and nameplate requirements use different current bases and rules.

Enter applicable table FLC, nameplate current, drive input current, manufacturer data, and protection factors from the adopted requirements.

Motor Current Basis

Conductors, overload protection, and branch short-circuit / ground-fault protection may use different current bases. Verify which basis applies to each check.

Special Motor Applications

VFD-fed motors, fire pumps, elevators, hermetic compressors, and multiple-motor circuits can require special sizing and protection review.