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Full-load amps (FLA)

Full-load amps (FLA) is the current a motor draws when it delivers its rated output at its rated voltage — the figure printed on the nameplate. It is the maker’s statement about that particular motor.

Nameplate FLA vs the code book’s value

The code book has its own full-load current values for motors, by horsepower and voltage, and they are a different figure for a different job. As a rule of thumb for the idea: the book’s values are used for sizing conductors and some protection, so the installation still works if the motor is swapped for another of the same rating; the nameplate FLA is what the overload is set to, because the overload protects this motor. Your code book says exactly which applies where. This site carries none of those table values.

What FLA tells you on the job

Measured current compared with the nameplate is one of the best quick checks there is. Well under FLA: the motor is lightly loaded. At or near FLA: it is doing its rated work. Over FLA: overloaded, low voltage, a phase problem, or a mechanical fault — find out which before the overload does it for you.

One worked, so the idea sticks

Checking a running motor against its nameplate

  1. The nameplate reads FLA 14 A at 460 V, service factor 1.15. (Practice numbers.)
  2. Clamp each phase: 12.9, 13.2 and 13.0 A.
  3. Average: (12.9 + 13.2 + 13.0) ÷ 3 = 13.03 A — 93% of the 14 A nameplate. Working hard, but within rating.
  4. The three phases sit within about 2% of the average of each other, so no phase trouble either.

The overload setting itself comes from the nameplate and your code book’s rules for it — follow those, not a percentage from here.

Questions fréquentes

Is FLA the same as the starting current?

No. Starting (inrush) current is several times FLA for a moment as the motor accelerates. FLA is the steady running current at full load.

What is the service factor?

A multiplier on the nameplate that says how far past its rated load the motor can run continuously without damage, under stated conditions. It has its own page.

Why does a motor draw less than FLA on the bench?

With nothing on the shaft, a motor draws only enough to overcome its own losses — often a fraction of FLA. It rises toward FLA as load goes on.

Voir aussi

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