Protecting HVAC Motor Bearings with Shaft Grounding Modules 

HVAC (Heating, Ventilation, and Air Conditioning) refers to systems that deliver heating and cooling for comfort in both commercial and residential properties. These systems use electric motors that respond to fluctuating heating and cooling requirements in buildings, including compressors, fans, and water pumps. The HVAC industry incorporates a wide range of businesses, from small family-run operations to larger corporations. This industry in the U.S. grew from just under 120,000 establishments in 2018 to almost 150,000 in 2023 [1]. Compared to electric motors that run at a constant speed, Variable Frequency Drives (VFDs) have become reliable and crucial for enhancing the efficiency and adaptability of HVAC systems. The global variable frequency drive market size is estimated at over 28 billion in 2024 and is projected to grow at almost 6% per year from 2025 to 2030 [2].  

However, variable frequency drives (VFDs) may generate voltage surges that have the potential to damage motor bearings. High-frequency pulse width modulation (PWM) signals from VFDs can cause electrical discharges that pit motor bearings. By implementing preventive measures to protect HVAC motors, using motor shaft grounding modules can improve the functionality, reliability, and longevity of HVAC systems. 

Aaki Corp.’s Motor Shaft Grounding Module (MSGM) provides a versatile, economical and reliable solution for managing shaft voltages caused by VFDs. Compatible with most motor configurations, they are ideal for a wide range of HVAC applications. These modules are available in two sizes, accommodating nearly any motor setup, ranging from fractional horsepower to several hundred HP. This module is designed to deliver enduring protection against harmful electrical currents. 

This article explores the basics of protecting HVAC motors using VFDs, discusses motor shaft grounding modules and highlights the importance of shaft grounding to help you make informed decisions for your applications. 

Key Advantages of VFDs in HVAC Motors: 

VFDs have gained huge popularity in the HVAC industry over the last two decades, offering several advantages over line powered methods. In various applications, they offer significant advantages, such as: 

1. Reduced Energy Consumption: VFDs ensure that energy consumption aligns with actual needs, preventing excessive power usage during low-demand periods.  

2. Enhanced System Control and Flexibility: Provide precise control and flexibility for HVAC components, enabling systems to function effectively under varying conditions. 

3. Prolonged Equipment Durability: Facilitate gradual starts and regulated deceleration considerably, enhancing the longevity of motors and associated equipment. 

4. Enhanced Air Quality: Enable HVAC systems to sustain consistent airflow and accurate temperature regulation, eliminating the frequent temperature variations typical of conventional systems. 

5. Load Distribution: Distribute the load among systems to prevent early failures, optimizing energy consumption throughout the entire facility.  

What is Shaft Grounding? 

High-frequency voltage fluctuations produced as a side effect of a VFD’s operation have the potential to couple to the shaft via the motor’s internal capacitance, building up a shaft voltage. This shaft voltage may pass through the bearing elements if the bearings are not protected, causing electrical arcing and bearing surface damage. Shaft grounding in HVAC motors is essential to protect motor bearings. A dedicated device connects the rotating shaft to the motor frame, allowing circulating currents to bypass the bearings and flow directly to ground.  

1. Carbon Brush Grounding Systems: Carbon brush grounding systems use solid bars made of high-conductivity materials, such as Aaki’s copper / graphite mixture, to carry electrical currents away from a rotating shaft and into the ground. Aaki MSGMs provide an excellent, durable contact surface area against the motor shaft and can be fit to any shaft diameter. They significantly reduce the risk of bearing failure due to electrical erosion or pitting.  

2. Shaft Grounding Ring (SGR): Shaft grounding rings incorporate fine wires or conductive fibers that surround the shaft. These rings protect the bearings from electrical damage.  However they need to be designed for a specific shaft diameter.  

Key Benefits of Shaft Grounding in HVAC Motors: 

1. Protection of Motor Bearings: A reliable shaft grounding method is required, ensuring long-lasting protection against bearing failures caused by stray current. 

2. Protection of equipment attached downstream of the Motor: Without shaft grounding, shaft voltages will try to find a way to ground, and will often travel through shafts and gears to other bearings in the drive train.  Motor shaft grounding prevents secondary bearing damage. 

3. Reduced Electrical Noise: Shaft grounding reduces electrical noise, improving the reliability and functionality of nearby sensors and electronics.  Motor Shaft grounding modules can often rid the facility of “ghosts in the machine” 

4. Increase Motor ROI: By installing a shaft grounding device on a motor, Return On Investment (ROI) can be increased significantly by preventing premature bearing failure leading to reduced maintenance costs and extended motor life span. 

Aaki’s Motor Shaft Grounding Module (MSGM): 

Aaki’s Motor Shaft Grounding Module (MSGM) delivers a robust grounding solution that safeguards electric motor bearings from harmful shaft voltages. Key features are:  

1. High-Performance Copper Graphite Brush: The high copper content (70%) provides an excellent, very low resistance path from the shaft to the motor housing effectively routing high current VFD induced voltage spikes.  

2. Brush Life Window™ Technology: The integrated Brush Life Window™ enables users or operators to easily monitor brush life at a glance. 

3. Higher Compatibility: This system is designed for seamless integration with our spacers and FleXmount™ brackets, facilitating a straightforward professional installation that accommodates various motor styles, making it an optimal choice for challenging industrial settings. 

4. One Size Fits Almost All: The simple design can be adapted to virtually any shaft diameter or motor frame size from fractional to hundreds of horsepower.  

5. Simple and Easy Installation: Simple installation process and compatibility with a diverse array of motor models and styles. Compact, low-profile design allows for installation in confined spaces.  

Technical Specifications 

Dimensions: 36mm x 42mm x 10mm (approx. 1.42 inches x 1.65 inches x 0.39 inches) 

Brush Surface Area: 70mm2 

Current: 10 Amp continuous current carrying capacity.  

Range: Slotted screw holes for a wide adjustment range. 

Compatibility: Compatible with motor models up to 100s of HP. 

Applications of HVAC Motors: 

HVAC motors are crucial because they power the fans and compressors within heating, ventilation, and air conditioning systems, essentially enabling the circulation of conditioned air throughout a building. They maintain comfortable temperature and humidity levels while ensuring proper air quality and are the driving force behind a functional HVAC system. There is a huge application of HVAC motors in different areas, such as: 

• Universities:  

1. Air Handling Units (AHUs): Drive AHUs, which are responsible for conditioning and distributing air effectively. 

2. Fan Coils: Power fan coils, which deliver heating and cooling to designated rooms or areas. 

3. Laboratory Ventilation: Regulate laboratory ventilation systems, ensuring a safe and healthy environment for both researchers and students. 

• Mission Critical Systems: 

1. Data Centers: Keep cooling server rooms by driving fans in air conditioning units  

2. Hospitals: Maintain precise temperatures in hospital rooms, operating rooms, intensive care units, and blood storage facilities.
     

3. Industrial Control Rooms: Regulate temperature for sensitive control systems.  

4. Cleanrooms: Maintain controlled air-conditioning for manufacturing processes. 

• Warehouses: 

1. Temperature Control: Drive fans, blowers, and pumps that circulate heated or cooled air throughout the warehouse, ensuring a stable temperature and humidity level. 

2. Ventilation: Power exhaust fans that eliminate stale air, dust, and pollutants from the warehouse, enhancing indoor air quality and preventing the accumulation of hazardous fumes. 

3. Air Filtration: Operate air filtration systems that remove dust, pollen, and other airborne pollutants, thereby improving air quality and safeguarding sensitive equipment. 

Conclusion: 

Shaft grounding devices are a critical component of HVAC motors, helping to ensure dependable operation and prevent premature bearing failure. It’s important to understand the various kinds of shaft grounding devices, their advantages, and the right procedures for installation and upkeep. Through the implementation of efficient shaft grounding solutions, industries can improve the HVAC motor’s longevity and dependability. When driven by VFDs, HVAC motors should employ some form of motor shaft grounding to increase reliability, increase efficiency, and lower maintenance costs. 

Aaki’s Motor Shaft Grounding Module (MSGM) offers a robust solution for preventing shaft voltage-related damage, ensuring reliable HVAC motor operation with reducing maintenance requirements. With features like simplified installation and Brush Life Window™ Technology, Aaki MSGMs are an ideal choice for safeguarding of HVAC motors.  

Contact Aaki today to learn more about how MSGMs can protect your HVAC motors and optimize your operations.