Full Load Amps (FLA) is the maximum continuous current a motor or electrical device is designed to draw while operating at its rated capacity, voltage, and frequency without exceeding its thermal limits. If you are wiring an air compressor, a table saw, or an industrial conveyor, the FLA is the single most important number on the equipment nameplate. It serves as the absolute baseline for sizing your branch circuit conductors, overload relays, and short-circuit protection. Misunderstanding this value—or confusing it with starting current—is the most common reason DIYers and junior electricians end up with tripped breakers or melted wire insulation.
The Core Concept: What Full Load Amps Actually Means
Think of FLA like a pickup truck towing a heavy trailer up a long, steady grade. The engine is working at its maximum continuous design limit; it can sustain this effort indefinitely without overheating, provided the cooling system (in a motor's case, the insulation class and cooling fins) is functioning properly. If you ask the motor to do more work than its rated horsepower, it will draw more current than the FLA, generate excess heat, and eventually degrade the winding insulation.
In a real circuit installation, the FLA changes everything about how you protect the system. According to the NFPA 70 (National Electrical Code), Article 430, you do not simply match your breaker to the FLA. Instead, the FLA acts as a multiplier base for three distinct protective layers:
- Conductor Sizing: Wires must be sized to carry at least 125% of the FLA to prevent the wire itself from acting as a heating element under continuous load.
- Overload Protection: Thermal overloads are typically set between 115% and 125% of the nameplate FLA to protect the motor windings from slow, continuous overcurrent.
- Short-Circuit/Ground-Fault Protection: Breakers or fuses are sized much higher (often 150% to 250% of the FLA) to allow the motor to start without tripping, while still protecting against catastrophic short circuits.
Full Load Amps Reference Table for AC Motors
When sizing wire and breakers, the NEC requires you to use standardized table values rather than the specific number printed on the motor's nameplate. This ensures that if a motor is replaced in the future with a slightly less efficient model, the wiring remains safe. Below is an excerpt from NEC Table 430.250 for 3-phase AC motors, which is the standard reference for industrial and heavy-duty workshop equipment.
| Motor Horsepower (HP) | 208V (3-Phase) | 230V (3-Phase) | 460V (3-Phase) | 575V (3-Phase) |
|---|---|---|---|---|
| 1 HP | 3.9 A | 3.6 A | 1.8 A | 1.4 A |
| 3 HP | 10.6 A | 9.6 A | 4.8 A | 3.9 A |
| 5 HP | 16.7 A | 15.2 A | 7.6 A | 6.1 A |
| 7.5 HP | 24.2 A | 22.0 A | 11.0 A | 9.0 A |
| 10 HP | 30.8 A | 28.0 A | 14.0 A | 11.0 A |
| 15 HP | 46.2 A | 42.0 A | 21.0 A | 17.0 A |
| 20 HP | 59.4 A | 54.0 A | 27.0 A | 22.0 A |
Worked Example: Sizing Wire and Breakers Using FLA
Let’s walk through a real-world installation. You are wiring a 7.5 HP, 230V, 3-phase air compressor in a workshop. You look at the motor nameplate, and it lists an FLA of 20.5A and a Service Factor (SF) of 1.15.
Step 1: Size the Conductors
Per NEC 430.22, we use the table value for 7.5 HP at 230V, which is 22A. We multiply by 125% for continuous duty: 22A × 1.25 = 27.5A. Looking at the 75°C column of NEC Table 310.16, 12 AWG copper is only rated for 25A (too small). We must step up to 10 AWG THHN copper wire, which is rated for 35A.
Step 2: Size the Overload Relay
For overloads, we switch to the nameplate value of 20.5A. Because the motor has a 1.15 Service Factor, NEC 430.32(A)(1) allows a maximum trip setting of 125%. 20.5A × 1.25 = 25.6A. You would set your adjustable thermal overload or select heater elements rated for 25.6A.
Step 3: Size the Short-Circuit Breaker
We return to the table value of 22A. For a standard inverse-time circuit breaker, NEC Table 430.52 allows a maximum rating of 250% of the FLA. 22A × 2.50 = 55A. Since 55A is not a standard breaker size (standard sizes are 40, 45, 50, 60), NEC 430.52(C)(1) Exception 1 allows you to round up to the next standard size. You will install a 60A 3-pole breaker.
Where You Meet FLA in Practice (And What People Confuse It With)
According to the U.S. Department of Energy Advanced Manufacturing Office, motor systems account for nearly a quarter of all electricity consumed in industrial facilities. Because of this, understanding current ratings is vital for energy audits and VFD (Variable Frequency Drive) programming. However, the nameplate is crowded with acronyms that are frequently confused with FLA.
Locked Rotor Amps (LRA)
LRA is the current the motor draws the instant power is applied, before the rotor begins to turn. It is typically 5 to 8 times higher than the FLA. If your 7.5 HP motor has an FLA of 22A, its LRA might be 135A. You use LRA to calculate voltage drop during startup and to size soft-starters or VFDs, but you never use it for continuous wire sizing.
Rated Load Amps (RLA)
If you are wiring a residential or commercial HVAC condenser unit, you will not see FLA on the nameplate; you will see RLA. RLA is a mathematical derivation created by UL (Underwriters Laboratories) specifically for hermetic refrigerant compressors. It is calculated by taking the maximum continuous current the compressor can draw without tripping its internal thermal protector, and dividing it by a specific factor (often 1.56). RLA is always lower than the actual physical FLA of the compressor motor.
Minimum Circuit Ampacity (MCA)
MCA is the HVAC industry’s equivalent to our wire-sizing calculation. It is a single number printed on the AC unit nameplate that already includes the 125% continuous load multiplier. If the MCA says 28A, you simply find a wire rated for at least 28A (e.g., 10 AWG) and skip the math.
Maximum Overcurrent Protection (MOCP)
MOCP is the HVAC equivalent to our breaker-sizing calculation. It tells you the absolute maximum breaker or fuse size allowed to protect the unit's internal wiring. If the MOCP says 40A, you cannot use a 45A breaker, even if the math suggests it might be close.
Frequently Asked Questions About Motor Current Ratings
Can a motor safely draw more than its FLA?
Only for very short durations. During startup, the motor draws LRA, which is vastly higher than FLA. Once running, if the mechanical load increases slightly, the current will rise above FLA. However, if it remains above FLA continuously, the winding insulation will degrade. This is exactly why thermal overload relays are installed—to trip the circuit if the current exceeds roughly 115-125% of FLA for an extended period.
Is Full Load Amps (FLA) the same as Full Load Current (FLC)?
Yes, in practical terms, they refer to the exact same concept. "FLC" is the terminology more commonly used in IEC (International Electrotechnical Commission) standards and European documentation, while "FLA" is the dominant term in North American NEC applications and NEMA (National Electrical Manufacturers Association) nameplates.
How do I measure actual FLA on a running motor?
Use a true-RMS clamp meter around one of the phase conductors while the motor is driving its actual mechanical load. Do not measure the motor while it is "unloaded" (e.g., a saw with the blade removed, or a pump running dry). An unloaded motor will draw significantly less current than its nameplate FLA—often only 30% to 50% of the rated value—because it is only overcoming internal friction and windage, not doing useful work.
