Motor Full-Load Amps (FLA) Calculator
The running current a motor draws — and the conductor amps that follow from it. Full-load current for three-phase, single-phase and DC motors, with the NEC 125 percent conductor figure.
Full-Load Amps: The Current That Sizes the Circuit
A motor full-load current is the current it draws at its rated output. It is the starting point for everything downstream — conductor size, overcurrent protection, contactor and overload selection. Get it wrong and the wire runs hot or the breaker nuisance-trips.
Single-phase drops the √3; DC drops both the √3 and the power factor. P is the mechanical output converted to watts (1 HP = 746 W), and dividing by efficiency accounts for the electrical input being larger than the shaft output.
The 125 Percent and 250 Percent Rules
For a continuously operating motor the NEC requires the branch-circuit conductors to be sized at 125 percent of the full-load current (430.22). The branch-circuit short-circuit and ground-fault protection — the breaker — may be set up to about 250 percent for an inverse-time breaker (430.52), then rounded to a standard size. The calculator reports both.
Use the Code Table, Not the Nameplate, for Sizing
This is the rule that trips people up. For sizing conductors and protection, the NEC requires the table values in 430.248 (single-phase) and 430.250 (three-phase), not the nameplate amps or a calculated figure. The table values are deliberately conservative and usually a little higher. Use this calculator to understand and estimate the current; size the actual circuit from the code tables.
Frequently Asked Questions
FLA, FLC or nameplate amps?
Full-load amps (FLA) and full-load current (FLC) are used loosely for the same thing, but the NEC table FLC is the legal sizing value. Nameplate amps reflect the specific motor and are used for overload protection.
Why divide by efficiency?
Because the electrical input power is larger than the mechanical output by the efficiency. A 90 percent motor draws about 11 percent more electrical power than its shaft horsepower suggests.
What power factor should I use?
Typical induction motors run 0.8 to 0.9 at full load, lower at part load. Use the nameplate value when available.
Related calculators
- Wire Size Calculator — turn the conductor amps into an AWG size.
- Three-Phase Power Calculator — the power behind the current.
- Voltage Drop Calculator — check the drop on the motor feeder.
- Engineering Unit Converter — HP, kW and more.