Motor Full-Load Amps (FLA) Calculator
Look up NEC table FLA and calculate conductor and OCPD sizing for motors.
| Full-Load Amps (FLA) | 7.6 A |
|---|---|
| Service Factor Amps | 7.6 A |
| Min Conductor Ampacity (125% FLA) | 9.5 A |
| Max Inverse-Time Breaker (250% FLA) | 19 A |
· FLA from NEC Table 430.248 (1φ) / 430.250 (3φ), approximate.
· Minimum conductor ampacity: 9.5A (125% of FLA per NEC 430.22).
· Maximum inverse-time breaker reference: 19A (250% of FLA). Select a standard OCPD per NEC 430.52 and 240.6.
· Verify nameplate FLA before final design. Actual FLA may differ from NEC tables.
How It Works
Motor circuits have their own sizing rules in NEC Article 430, separate from general branch circuits. Full-load amps (FLA) come from NEC Tables 430.248 (single-phase) or 430.250 (three-phase). These are table values, not necessarily the actual nameplate FLA. Whenever possible, use the nameplate for final design. Key rules: - Minimum conductor ampacity = 125% of FLA (NEC 430.22) - Maximum inverse-time circuit breaker = 250% of FLA (NEC 430.52, Table 430.52) - Service factor amps (SFA) from the nameplate is the maximum continuous current the motor can handle with its built-in service factor; it is higher than FLA.
Example
5 HP, 3-phase, 460 V: FLA = 7.6 A. Min conductor = 7.6 x 1.25 = 9.5 A. Max breaker = 7.6 x 2.5 = 19 A, so use the next standard size at or below 19 A.
Frequently Asked Questions
Why use table FLA instead of nameplate FLA?
NEC tables are used for conductor and OCPD sizing when nameplate data isn't available at design time. Always verify with actual nameplate data during installation.
Can I use a smaller breaker than 250% for better protection?
Yes. You can size down, as long as the motor starts reliably. Smaller breakers trip less often on running overloads, which is fine. The 250% is a maximum, not a target.
What about motor starters and overloads?
Separate overload protection is required per NEC 430.32. This calculator covers the branch circuit conductor and OCPD only.