Motor Full Load Current Calculator

Look up 3-phase motor full load amps (FLA) per NEC Table 430.250 and calculate conductor ampacity, OCPD, and disconnect ratings.

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How to Calculate Motor Full Load Current

What Is Motor Full Load Current (FLA)?

Full load current (FLA) is the steady-state current a motor draws at its rated horsepower and voltage under full load conditions. NEC Table 430.250 provides the authoritative FLA values for 3-phase AC motors. These values are used (not the motor nameplate) for sizing conductors, overcurrent protection, and disconnecting means.

NEC Table 430.250 — The FLA Lookup

FLA: Look up from NEC Table 430.250 based on HP and voltage.

Conductor Ampacity: FLA × 125% (NEC 430.22)

OCPD Rating: Next standard size ≥ FLA × 175% (NEC 430.52, inverse-time breaker)

Disconnect Rating: Next standard size ≥ FLA × 115% (NEC 430.110)

For synchronous motors, apply a 0.9 power factor multiplier to the induction FLA values.

Worked Example: 10 HP Motor at 460V

FLA (NEC 430.250): 14.0 A
Conductor ampacity (× 1.25): 14.0 × 1.25 = 17.5 A
OCPD rating (× 1.75): 14.0 × 1.75 = 24.5 → next standard = 25 A
Disconnect rating (× 1.15): 14.0 × 1.15 = 16.1 → next standard = 20 A

Practical Tips

Always use NEC Table 430.250 values for branch circuit sizing — not the motor nameplate current.
For motors ≥ 100 HP at low voltage, check NEC 430.52(C)(1) Exception 2 for higher OCPD percentages.
Synchronous motors operate at leading power factor; the 0.9 PF multiplier is a convention for approximate calculation.
3 HP and larger motors are not typically available at 115V (table shows N/A).

Code References

NEC 430.250, NEC 430.22, NEC 430.52, NEC 430.110

Frequently Asked Questions

Should I use the motor nameplate amps or NEC Table 430.250?

For sizing conductors, overcurrent protection, and disconnecting means, NEC requires using the values from Table 430.250 — not the motor nameplate FLA. The nameplate may differ due to motor efficiency and design variations.

Why multiply FLA by 1.25 for conductor sizing?

NEC 430.22 requires motor branch circuit conductors to have an ampacity of at least 125% of the motor full load current. This accounts for the sustained current draw during motor operation and provides thermal margin.

How do I size OCPD for a motor circuit?

Per NEC 430.52, the motor branch circuit OCPD must be sized at 175% of FLA for an inverse-time breaker (typical), then rounded up to the next standard size. For motors with high inrush (e.g., NEMA Design B), higher percentages may apply.

What is the difference between induction and synchronous motor FLA?

Induction motors are the most common type. Synchronous motors run at a fixed speed and operate at leading power factor. For approximate synchronous FLA, multiply the induction table value by 0.9 (90% power factor convention).