If the service factor for a motor is not given on the nameplate, what should you assume the service factor to be?

When the service factor for a motor is not specified on the nameplate, it is standard practice to assume a service factor of 1.0. This is because a service factor of 1.0 indicates that the motor is rated for its full load capacity, meaning it is designed to operate at its rated horsepower under standard conditions without any additional safety margin or overload capability.

If a motor's service factor is not listed, it typically indicates that the manufacturer expects the motor to operate reliably at its rated capacity without any excess operational demands placed upon it. Motors with higher service factors, such as 1.2, 1.5, or 2.0, are engineered to handle short-duration overload conditions better but when no service factor is indicated, assuming 1.0 is the most conservative and commonly accepted assumption in motor applications and sizing.

This approach ensures that you design and select equipment and systems based on reliable performance expectations. Therefore, assuming a service factor of 1.0 aligns with industry standards and best practices.