Fractional-Horsepower Motor Explained

As HVAC professionals, it’s essential to understand the various components that contribute to system efficiency and reliability. One such component is the fractional-horsepower (FHP) motor. In this post, we will delve into what fractional-horsepower motors are, their specifications, and their applications in HVAC systems.

What is a Fractional-Horsepower Motor?

A fractional-horsepower motor is defined as a motor usually built in a frame smaller than one horsepower with an open construction design. These motors typically operate at speeds of around 1700 to 1800 rpm. Within the National Electrical Manufacturers Association (NEMA) framework, the FHP category includes frame sizes 42, 48, and 56.

Key Characteristics of Fractional-Horsepower Motors

• Frame Size: While the motor rating may exceed one horsepower, its frame size confines it to the fractional category. Understanding frame sizes is crucial for proper integration into HVAC units.
• Speed Ratings: Most FHP motors operate at a speed of 1700–1800 rpm, ideal for many HVAC applications where speed control and energy efficiency are critical.
• Construction: FHP motors are open construction, which allows for better thermal management—an important factor in HVAC systems to prevent overheating.

Calculating Frame Height

One interesting aspect of fractional-horsepower motors is how to determine their height. You can calculate the height from the center of the shaft to the bottom of the base by dividing the frame size by 16. For example, a motor with a frame size of 48 would have a height of 3 inches.

Applications in HVAC Systems

Fractional-horsepower motors find extensive applications in HVAC systems, including:

• Fans: Used in air handling units, exhaust systems, and condenser fans where variable speeds are necessary.
• Pumps: Commonly found in circulation pumps that require efficient and effective flow management.
• Compressors: Utilized in small compressors and refrigerant systems.

Conclusion

Understanding fractional-horsepower motors is crucial for HVAC professionals as they play a pivotal role in system performance. By being familiar with their specifications and applications, you can ensure greater efficiency, reliability, and longevity in the systems you work with. Whether you are replacing an existing motor or selecting a new one, consider the significance of FHP motors in your HVAC arsenal.