Locked Rotor Amps Calculator

Formula

The formula to calculate Locked Rotor Amps (LRA) is:

\[ \text{LRA} = 1000 \times \left(\frac{\text{kVA}}{\text{HP}}\right) / \text{V} \]

Where:

\(\text{LRA}\) is the locked rotor amps
\(\text{kVA}\) is the kilovolt-amps
\(\text{HP}\) is the horsepower
\(\text{V}\) is the voltage

What are Locked Rotor Amps?

Locked rotor amps are defined as the inrush current received by a motor or generator when it starts up. This current is significantly higher than the normal operating current and occurs because the motor is not yet rotating, hence the term "locked rotor."

Example Calculation

Let's assume the following values:

Kilovolt-Amps (kVA) = 10 kVA
Horsepower (HP) = 5 HP
Voltage (V) = 230 V

Using the formula to calculate the Locked Rotor Amps (LRA):

\[ \text{LRA} = 1000 \times \left(\frac{10}{5}\right) / 230 = 8.70 \text{ A} \]

The Locked Rotor Amps (LRA) is 8.70 A.