Motor FLC, FLA, and Branch-Circuit Sizing

The first split: FLC vs FLA

The exam will hand you both numbers when it wants to test whether you know the job of each number.

• FLC means full-load current from NEC motor tables. Use it for branch-circuit conductor sizing and short-circuit ground-fault protection.
• FLA means full-load amps from the motor nameplate. Use it for overload protection.
• Table 430.250 is the high-frequency table for three-phase motor FLC.

If you want the table-only explanation, use the NEC Table 430.250 guide.

The four motor sizing decisions

1. Single motor branch-circuit conductor: 125% of table FLC.
2. Motor overload protection: nameplate FLA, with the Article 430 overload percentage.
3. Branch-circuit short-circuit and ground-fault protection: Table 430.52 percentage of table FLC.
4. Multiple motor feeder conductor: 125% of the largest motor FLC plus 100% of the others.

Worked example: 25 HP, 460 V, three-phase motor

A 25 HP, 460 V, three-phase squirrel-cage motor has table FLC of 34 A. The question asks for minimum branch-circuit conductor ampacity. What is the number before choosing the conductor size?

1. Name the sizing decision: branch-circuit conductor for one motor.
2. Use table FLC, not nameplate FLA.
3. Apply 125%: 34 A x 1.25 = 42.5 A.
4. Minimum conductor ampacity before selecting a conductor: 42.5 A.
5. If the next question asks for the inverse-time breaker, do not reuse 42.5 A. That is a different Article 430 decision.

Why motor breakers look too big

A motor has starting current. That is why the short-circuit and ground-fault protective device can be sized much higher than the branch-circuit conductor ampacity. The breaker or fuse in that question is not doing the same job as overload protection.

For a common three-phase squirrel-cage motor, Table 430.52 may allow an inverse-time breaker at a percentage much higher than 125% of FLC. That does not mean the conductor was sized wrong. It means the conductor, overload device, and SCGF device each have a separate job.

Wrong answers the exam wants you to pick

Using FLA when the rule wants FLC

Nameplate FLA belongs to overload protection. Table FLC belongs to branch-circuit conductors and SCGF protection.

Applying 125% to every motor on a feeder

Multiple motor feeder sizing uses 125% of the largest motor plus 100% of the others. Do not multiply every motor by 125%.

Using the conductor answer as the breaker answer

The 42.5 A branch-circuit conductor result in the example is not the breaker answer. The breaker question sends you to Table 430.52.

How to drill this for the exam

Write four labels on your scratch paper: conductor, overload, SCGF, feeder. Every motor question belongs under one of those labels. If you cannot name the label in 10 seconds, do not start the math yet.