FLA vs FLC vs MCA: The Three Motor Current Numbers

What FLA means in electrical work

FLA is full-load amps. It is the current a specific motor draws at rated horsepower and rated voltage, measured by the manufacturer and stamped on the nameplate. It describes the motor in front of you, not a category of motors. Two 10 HP motors from two manufacturers can carry different FLAs, and both nameplates are right.

In the NEC, the nameplate number has exactly one job on the exam: overload protection. Per 430.6(A)(2), separate motor overload protection is based on the nameplate current rating, and 430.32 sets the multipliers. That makes sense on the truck. Overloads exist to keep this motor from cooking its windings, so they follow the real number for this motor.

What FLC means and where the tables live

FLC is full-load current from the NEC tables. Table 430.248 covers single-phase motors. Table 430.250 covers three-phase motors. Tab both. Per 430.6(A)(1), these table values, not the nameplate, are what you use to size conductors and branch-circuit short-circuit and ground-fault protection.

Even when the nameplate disagrees. That trips people up, so here is the reasoning. The wiring has to outlive the motor. When that motor burns up in eight years and the replacement shows a slightly higher nameplate FLA, conductors sized from the standard table value are still legal. Conductors sized from the old nameplate might not be. The table protects the installation. The nameplate protects the motor.

What MCA means on an HVAC nameplate

MCA is minimum circuit ampacity, and it lives on a different kind of nameplate. Listed HVAC and refrigeration equipment, the condenser on the pad, the rooftop unit, carries an MCA marking per 440.4(B). The manufacturer has already run the math under the UL product standard: 125 percent of the largest motor plus the other loads in the box. That is the same figuring 440.32 and 440.33 require for the conductors: 125 percent of the single motor-compressor, or the sum of the group plus 25 percent of the largest.

Your job with MCA is simple. Pick branch-circuit conductors with an ampacity of at least the MCA. Do not multiply it by 125 percent again. The factor is already inside the number, and doubling it up is a classic wrong answer on HVAC questions.

One more wrinkle. Hermetic refrigerant motor-compressors show RLA, rated-load amps, instead of FLA, because a sealed compressor never runs outside its refrigerant. Those fall under Article 440, not Article 430. If the question says hermetic compressor or shows an MCA, you are in 440 territory.

The exam trap: conductors from the table, overloads from the nameplate

This is the whole page in one rule, and it is where most motor points die. When the exam compares FLA vs FLC, it is really asking one question: do you know which number feeds which calculation?

• Conductors (430.22): table FLC. Single continuous-duty motor conductors need an ampacity of at least 125 percent of the table value.
• Branch-circuit short-circuit and ground-fault protection (430.52): table FLC. The percentages in Table 430.52(C)(1) start from the table value too.
• Disconnect rating (430.110): table FLC. At least 115 percent of the table value.
• Overload protection (430.32): nameplate FLA. This is the only calculation in the family that touches the nameplate.

The exam writers know candidates blur these. So the question stem hands you both numbers: a horsepower rating that points to the table, and a nameplate FLA that sits a couple amps lower. Then the answer choices include the result of running the math on each one. Grab the wrong number and you land on a clean, confident, wrong answer.

Worked example: 10 HP, 230V, three-phase motor

One motor, two calculations, two different starting numbers. A 10 HP, 230V, three-phase, continuous-duty motor with a nameplate FLA of 26A and a service factor of 1.15.

Conductors: start from the table

Table 430.250 lists 28A for a 10 HP, 230V, three-phase motor. The nameplate says 26A. Ignore it here. Per 430.22, minimum conductor ampacity is 28A x 1.25 = 35A.

Overloads: start from the nameplate

Service factor is 1.15, so 430.32(A)(1) allows overloads sized at a maximum of 125 percent of nameplate FLA. That is 26A x 1.25 = 32.5A. The table value never enters this calculation. If the service factor were under 1.15 and the temperature rise over 40 degrees C, the multiplier drops to 115 percent.

When to use FLC vs FLA: the quick rules

• Question asks for conductor size or ampacity: table FLC (430.6(A)(1), 430.22).
• Question asks for the breaker or fuse feeding the motor circuit: table FLC with the Table 430.52(C)(1) percentages.
• Question asks for the disconnect rating: table FLC (430.110).
• Question asks for overload sizing, heater selection, or motor protection: nameplate FLA (430.32).
• Nameplate shows an MCA: the conductor math is already done, match or beat that ampacity (440.4(B)).

FLA vs MCA: do not compare them directly

FLA is a motor number. MCA is an equipment number that already includes the 125 percent factor plus every other load in the cabinet: compressor, condenser fan, control transformer. So the MCA on a condenser will always be bigger than the compressor RLA alone, and that is not a mistake on the nameplate. When an exam question gives you an MCA, it has done the Article 440 work for you. The remaining step is picking a conductor whose ampacity meets or beats it.

FLA vs FLC vs MCA: quick answers