Determination of Motor Full-Load Current

MotorsNEC 2023CEC Equivalent: CEC Rule 28-100

Every motor has a nameplate that lists its full-load amperes (FLA). You might assume that number is what you use for everything — but the NEC says otherwise. The tables in the back of Article 430 list generic full-load current (FLC) values based on horsepower, voltage, and phase. These table values are typically higher than what any individual motor's nameplate shows because they account for the range of efficiencies and power factors across different manufacturers and motor designs. The idea is to build in a margin of safety. You use these table values for sizing your branch-circuit conductors, your disconnect switch, and your short-circuit protection device. However, for the motor overload device (the component that protects the motor itself from prolonged overcurrent), you switch back to the nameplate FLA — because the overload must be matched closely to the specific motor it is protecting.

When You Need This

Sizing conductors for a new motor installation — you need the table FLC, not the nameplate value
Selecting a disconnect switch or branch-circuit breaker for a motor circuit
Choosing the correct motor overload relay heater — this is the one time you use the nameplate FLA
Performing a load calculation for a facility with multiple motors
Answering exam questions that test whether you know the table-vs-nameplate distinction

Key Points

1Use NEC Table FLC values (Tables 430.247-430.250) for conductor sizing, disconnect ratings, and short-circuit protection

2Use the nameplate FLA only for motor overload protection sizing

3Table values are intentionally higher than most nameplate values to cover the range of motor designs on the market

4For low-speed motors (below 1,200 RPM) or high-torque motors, use the nameplate current for everything because the tables may not represent them accurately

5For multispeed motors, use the nameplate current for each speed because the tables do not cover variable-speed ratings

6This dual-current approach is one of the most tested concepts on electrical licensing exams

Common Mistakes

Using the motor nameplate current for conductor sizing — the NEC requires the table values instead

Using the table value for overload protection — this is the one place where the nameplate FLA must be used

Looking up a 3-phase motor in the single-phase table or vice versa

Forgetting that low-speed and high-torque motors are exceptions that use nameplate values for everything

Confusing FLC (full-load current from the NEC tables) with FLA (full-load amperes from the nameplate)

Exam Tip

Remember this simple rule: TABLE for the circuit, NAMEPLATE for the overload. If the exam question asks about conductor or breaker sizing, use the table. If it asks about the overload device, use the nameplate FLA.

Frequently Asked Questions

Different manufacturers build motors with different efficiencies and power factors, so a 10-HP motor from one brand might draw 26 amps while another draws 28 amps. The NEC tables use a conservative value that safely covers the full range. This way, if you swap a motor later, the circuit is still properly protected.

Table 430.250 covers three-phase AC motors. Table 430.248 covers single-phase AC motors. Table 430.247 covers DC motors. Table 430.249 covers two-phase motors, which are very rare.

This can happen with low-speed or high-torque motors. In that case, the NEC says to use the nameplate current for all calculations, not the table value.

Inline Tools

Motor FLC Calculator

Look up full-load current for any motor HP and voltage

Related Code Sections

430.22Single Motor Branch-Circuit Conductor Sizing 430.52Motor Branch-Circuit Short-Circuit and Ground-Fault Protection

This is an educational summary, not the official code text. The NEC® is a registered trademark and copyright © National Fire Protection Association (NFPA). The CEC is copyright © CSA Group. For official code text, visit nfpa.org or csagroup.org. SparkShift is not affiliated with NFPA or CSA Group.