What is the lock rotor current for a 1 1/2 HP single-phase 208-volt motor?

To determine the lock rotor current for a 1 1/2 HP single-phase 208-volt motor, it's important to understand the relationship between the horsepower and the electrical current during the starting phase of the motor.

Lock rotor current (LRC) is typically several times higher than the full load current and is present when the motor is starting, as the rotor is not yet turning and the motor draws maximum current. The general formula to estimate the LRC for single-phase motors involves taking the full load current and multiplying it by an appropriate value, often around 6 to 8 times the full load current, depending on the motor's design characteristics.

The full load current for a 1 1/2 HP motor at 208 volts can be calculated using the formula:

Full Load Current (FLA) = (Horsepower × 746) / (Voltage × Efficiency × Power Factor)

Assuming a typical efficiency of about 90% and a power factor of about 0.8 for such a motor, the full load current would be approximately 8.5 to 9 amps. Multiplying this FLA by 7 (a common multiplier for estimating LRC) results in a lock rotor current of approximately 66 amps