Bearing rings installed on the VFDs at the Time & Life Building in New York’s Rockefeller Center protect from electrical bearing damage.

Preventive maintenance at a prominent Manhattan building illustrates a widespread problem with HVAC motors: electrical bearing damage.

Typical fan or pump motors use less power if the input is modulated by VFDs, but the benefits of improved efficiency are lost if these motors break down. That is what happened regularly for more than two decades at the 48-story Time & Life Building in Rockefeller Center.

The high maintenance costs were due to unwanted high-frequency currents induced by VFDs. Without mitigation, these currents discharge from a motor’s shaft to its bearings, leaving pits in ball bearings and bearing race walls. Concentrated pitting at regular intervals along a race wall can cause washboard-like ridges called fluting, a source of noise and vibration. By this time, bearing failure is often imminent.

Ironically, some products designed to protect bearings, such as conventional spring-loaded grounding brushes, require extensive maintenance themselves. Others, such as ceramic bearings, can shift damage to connected equipment.

One of the newest and most promising devices is the maintenance-free AEGIS™ SGR bearing protection ring by Electro Static Technology, which provides a very low impedance path from shaft to frame, bypassing bearings. To boost the electron-transfer rate, conductive microfibers line the ring’s entire inner circumference.

“The whole phenomenon of electrical bearing damage is so misunderstood that some maintenance managers have lost their jobs over it,” explains Tom O’Connell Jr., a partner in AKF Analysis & Testing (AKFA&T), an engineering firm hired by the Rockefeller Group Development Corporation to periodically test and tune the building’s VFDs.


Late in 2007, O’Connell suggested installing an AEGIS SGR on a 50-hp fan motor at Time & Life that was notorious for running hot and making a lot of noise due to short-lived bearings. Ron Perez, the building’s manager of engineering, called it “one of the most annoying motors in the building.” He consented to the experiment, and the ring was installed in February 2008. Follow-up testing proved the SGR successful.

Since the AEGIS SGR was installed, the motor has run quietly and at least 100° cooler. Tests two weeks after the installation showed negligible shaft currents. A year later, the voltage was even lower. Perez concluded the ring had solved the problem. As of February 2010, he had installed AEGIS SGRs on 39 additional fan motors at Time & Life.

O’Connell now recommends the SGR be installed on all existing HVAC motors and specified for new buildings, estimating it will reduce repair costs by approximately 10%. “Now,” he notes, “with the AEGIS SGR I can show a customer how the ring improves his equipment - immediately. The SGR is the answer.”

Installed on a VFD-controlled motor, the AEGIS SGR bearing protection ring requires no maintenance, lasts for the life of the motor, and qualifies as sustainable technology under the Federal Energy Management Program.

VFDs hold the promise of sizable energy savings, but without effective, long-term bearing protection such as the AEGIS™ SGR those savings could be wiped out by high motor-maintenance costs. By making VFD energy savings sustainable, the AEGIS™ SGR provides a truly green solution.ES