The Reliability Files

Extending The Life Of Energy-Efficient HVAC Equipment

EP Editorial Staff | November 21, 2011


A leading plastic-injection company planned to install variable frequency drives (VFDs) on its chiller pumps to increase energy efficiency and reduce operating costs. These drives are increasingly popular in the HVAC industry because of their ability to economically meet changing load demands, making them ideal for fluid and air-flow applications.

While the use of VFD systems provides many benefits, the company was concerned because VFDs have been known to cause premature bearing failure: They induce high-frequency voltages on the shaft that seek the path of least resistance to ground. These harmful shaft currents discharge through the motor’s bearings or the bearings of coupled equipment. Once these voltages exceed the insulation breakdown of the bearing lubricant, they discharge through the bearings to ground.

This discharge—known as electrical discharge machining (EDM)—is one of the leading causes of premature bearing failure in VFD-driven motors. The results are costly:  They include reduced equipment reliability, increased maintenance costs, unscheduled downtime and lost revenue.

The customer specified to its vendor of choice, the full-service HVAC energy- solutions provider Gardiner Trane, that bearing protection be added to the VFD installation project to safeguard the owner’s investment. Gardiner Trane chose the Inpro/Seal® Current Diverter Ring™ (CDR®) as its complete shaft-grounding solution. The CDR® utilizes proprietary conductive filaments to divert harmful shaft currents from the bearings and to ground by providing a low-impedance path to ground away from the bearings.

“Originally we were going to use a complete ring assembly,” said William Thompson of Gardiner Trane, “but after consulting Inpro/Seal’s application engineers, they recommended a split design for easy installation.” Thompson explained that Inpro/Seal’s ability to custom engineer a split-design CDR® for each piece of equipment was an attractive feature to Gardiner Trane because of shaft-diameter variations on their customer’s motors. “The pumps are close coupled and getting the correct measurement was difficult,” he said. “Getting the size right was critically important.”


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Return On Investment
Nineteen custom-engineered CDR® devices were delivered to Gardiner Trane in 1-2 days time. Gardiner Trane installed them on Sundays so the process wouldn’t interrupt the customer’s production schedule. “Inpro/Seal’s sales engineer guided us through the installation process and, with his help, the few issues we had were easily resolved,” Thompson said.

Since the CDR® devices were installed, Gardiner Trane and its customer have observed no evidence of bearing damage. “We service this customer with an ongoing agreement for their HVAC equipment and assist with the operation of the pump skids, if needed. Since we installed the CDR® devices there have not been any issues— the original bearings are still operating with the new VFDs.” Thompson stated that thanks to the bearing protection Inpro/Seal provides, the customer is able to enjoy all the energy-efficiency and cost-savings benefits VFDs offer without fear of premature bearing wear, motor failure or costly downtime. MT

Rock Island, IL

Inpro/Seal is the leading designer and manufacturer of engineered-system and bearing-protection products for rotating equipment in a variety of industries. Since inventing the first bearing isolator in 1977, Inpro/Seal has maintained a leadership position in the markets they serve. The company’s complete shaft-grounding solutions include the Current Diverter Ring (CDR®), multi-stage CDR® for high-voltage systems and Motor Grounding Seal (MGS®) for severe duty applications. Learn more about Inpro/Seal at

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