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Motor FLA & Protection Sizer

Estimate motor FLA to recommend contactor, overload, and breaker sizes.

Motor Details

Estimated from NEC 430.248/250. You can override this value.

Sizing Results

Max Breaker/Fuse Size 0 A
Max Overload Relay 0 A
Min Wire Ampacity (125%) 0 A
Note: Sizes are absolute maximums per NEC. Standard sizes should not exceed these values.
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Disclaimer of Liability: This calculator is provided for educational and estimation purposes only. By using this tool, you agree to discharge AutomationView of any liability for direct, indirect, or consequential damages resulting from its use. It is your strict responsibility to independently verify all calculations, validate the results against official manufacturer documentation, and ensure compliance with all applicable safety and engineering standards before implementing any parameters in a production environment.

The Critical Distinction: FLC vs. FLA

When sizing motor circuits for industrial automation in compliance with NEC Article 430, the most common error is confusing Full-Load Current (FLC) with Full-Load Amperes (FLA). Understanding this distinction is vital for safety and code compliance.

  • Full-Load Current (FLC): You must use the values found in NEC Tables 430.248 (1-phase) or 430.250 (3-phase) for sizing branch-circuit conductors and short-circuit/ground-fault protective devices. Never use the nameplate FLA for these calculations.
  • Full-Load Amperes (FLA): Use the actual motor nameplate rating only when sizing the separate overload protection.

Sizing Steps for Motor Branch Circuits

A. Branch-Circuit Conductors

Conductors must be sized at a minimum of 125% of the motor FLC as determined by the NEC tables.

B. Short-Circuit and Ground-Fault Protection (SCGFP)

This protection defends the conductors and controller against high-level faults. Sizing is based on the motor FLC and the device type (NEC Table 430.52). For example, an Inverse-Time Circuit Breaker is typically sized at 250% of FLC, while a Dual-Element Fuse is sized at 175%.

C. Motor Overload Protection

Overload protection prevents the motor from overheating due to excessive load. It is calculated based on the motor nameplate FLA. Standard sizing is usually 125% for motors with a service factor of 1.15 or greater, and 115% for others.

Important Considerations for Automation

Keep in mind that motors draw 6–8 times their FLC during startup. Additionally, installations involving Variable Frequency Drives (VFDs) often require adhering to the drive manufacturer’s specific instructions for input protection. Using a dedicated Motor FLA & Protection Sizer can streamline these complex NEC calculations.