Full Load Amps Calculator - 3 Phase Motor Starter

3-Phase Motor FLA Formula:

\[ FLA = \frac{Power \times 1000}{\sqrt{3} \times Voltage \times Power\ Factor \times Efficiency} \]

Power:

Voltage:

Power Factor:

(0-1)

Efficiency:

(0-1)

Full Load Amps (FLA):

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1. What is Full Load Amps (FLA)?

Full Load Amps (FLA) is the current a motor draws while operating at its rated load, voltage, and frequency. It's a critical parameter for selecting motor starters, overload protection devices, and wiring.

2. How Does the Calculator Work?

The calculator uses the standard 3-phase motor FLA formula:

\[ FLA = \frac{Power \times 1000}{\sqrt{3} \times Voltage \times Power\ Factor \times Efficiency} \]

Where:

\( Power \) — Motor power rating in kilowatts (kW)
\( Voltage \) — Line-to-line voltage in volts (V)
\( Power\ Factor \) — Ratio of real power to apparent power (typically 0.8-0.95)
\( Efficiency \) — Motor efficiency as a decimal (typically 0.8-0.95)

Explanation: The formula converts kW to watts (×1000), accounts for 3-phase power (√3), and adjusts for power factor and motor efficiency losses.

3. Importance of FLA Calculation

Details: Accurate FLA calculation is essential for proper motor protection, preventing nuisance tripping while ensuring protection against overload conditions. It's used to size circuit breakers, fuses, contactors, and overload relays.

4. Using the Calculator

Tips: Enter motor power rating in kW, line voltage in volts, and typical power factor and efficiency values (defaults provided). For precise calculations, use manufacturer-specified power factor and efficiency values.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between FLA and RLA?
A: FLA (Full Load Amps) is at rated load, while RLA (Rated Load Amps) is the maximum current under expected operating conditions (often slightly higher than FLA).

Q2: How does voltage affect FLA?
A: FLA is inversely proportional to voltage. A motor running at lower voltage will draw higher current to deliver the same power.

Q3: What are typical power factor values?
A: Induction motors typically have power factors of 0.85-0.90 at full load, lower at partial loads. Synchronous motors can achieve 1.0 or leading power factors.

Q4: Why include efficiency in the calculation?
A: Efficiency accounts for power losses in the motor (heat, friction, etc.). A less efficient motor draws more current to deliver the same output power.

Q5: How should FLA be used in motor protection?
A: Overload protection devices should be sized at 125% of FLA for most applications, per NEC guidelines.