AEGIS Rings have worked for years to improve reliability and sustainable operatuion of HVAC and Pump motors.   Case in point: Harvard University’s Campus services Facility Maintenance Operations (FMO) “offers Motor Shaft Grounding, a maintenance program that prevents bearing failure and significantly extends motor life.”


Variable frequency drives (VFDs) present a compelling option for energy savings in sustainable building projects. Power usage in continuously running centrifugal pumps and fans decreases notably with input modulation by a VFD. For example, a 20% reduction in fan speed can reduce energy consumption by nearly 50%. VFDs also introduce their own sustainability problems, however. VFD-induced shaft currents can damage bearings, leading to shorter motor life and costly repairs. Shaft grounding technology such as the AEGIS Shaft Grounding Ring offers a sustainable solution to this problem. Unfortunately, most new construction projects including VFD-driven motors do not utilize this effective option.

The university maintenance department has spearheaded a campus-wide sustainability drive starting with their own Platinum LEED certified headquarters. A major component of this has been a testing program for VFD-driven HVAC motors. Maintenance technicians employ oscilloscopes and voltage measuring probes to ascertain the presence of shaft voltage. When harmful voltage levels are detected, the maintenance department may recommend the installation of an AEGIS ring. Already successfully employed in multiple new buildings on campus, expanding the AEGIS ring to existing motor setups that require bearing protection continues to increase campus-wide sustainability.

The University Test Case

In December 2009, the ring’s manufacturers installed their product on two VFD-controlled HVAC motors in the maintenance headquarters building as a demonstration of the new program. The identical three year old Baldor 7.5HP motors respectively powered a chilled water pump and an air supply fan. With the VFD set at 60HZ, the first motor was running at 1,776rpm. The oscilloscope measured peak-to-peak discharges of 61 volts. Results showed rapid voltage collapses at the trailing edge of the waveform, typical of the electrical discharges that damage bearings. After the reading, technicians cleaned the shaft and installed a split AEGIS ring. Follow-up test results displayed the discharge plot as a straight line, indicating that the AEGIS ring diverted shaft voltage discharges.

Pump Motor with AEGIS Ring installed with EP2400 Conductive Epoxy

The second motor was tested under identical conditions and measured 50.8 volts peak-to-peak shaft discharge. Due to the limited accessibility of this motor, application of a hand-held heater sped epoxy curing in the AEGIS ring installation. After the complete installation, a new test read only 380 millivolts peak-to-peak, again indicating the AEGIS ring successfully diverted shaft voltage discharges to ground.


VFDs provide a compelling option for energy savings in sustainability-minded design. However, unless a product such as the AEGIS Shaft Grounding Ring mitigates the risk of bearing damage, repair costs could outweigh any savings. While this problem remains best addressed in the design stage of the system, the university case study effectively demonstrates the potential to retrofit previously installed motors with shaft grounding technology. Once installed, an AEGIS ring requires no maintenance and lasts for the life of the motor, providing effective protection against shaft voltage.

An array of motors with AEGIS factory-installed http://www.est-aegis.com/oems.php

Most motor manufacturers have product lines with AEGIS Rings factory installed.

More information about the university case study can be found here.

UL Approval for AEGIS® Grounding Rings for Hazardous Environments – Class 1 Division 1, Zone 1

Underwriters Laboratories (UL) has an approved set of procedures for installing AEGIS® shaft grounding rings inside explosion proof (XP) motors. XP motors with AEGIS® rings installed according to these procedures may be used in hazardous environments, Class I: Division 1.

The following diagrams are the approved installation locations inside the XP motor.

Detail of AEGIS Shaft Grounding Ring in XP motors

Note: In Class I: Division 2 designs. Because shaft grounding devices must be installed inside explosion proof enclosures (as per IEEE 303) for Class I: Division 2, they may not be installed internally or externally in/on a non-XP motor.

Diagram of location to install AEGIS Rings inside the XP motors

At this time, Marathon Electric is the only electric motor manufacturer marketing XP motors with AEGIS® shaft grounding protection installed inside. They range from 3 HP (182T Frame) to 50 HP (326T Frame) and Marathon Electric will install AEGIS Rings in larger models.  For more information on Marathon Hazardous Duty motors with AEGIS® Inside.   For catalog numbers and pricing, see the highlighted “-P” motors on the Hazardous Duty™ pages of the 2014 catalog.

UL Approved Electric Motor Repair Companies

To install AEGIS® rings in explosion proof motors in a hazardous environment, a motor repair shop must first be UL approved to work on all XP motors. They must then apply for certification for the addition of adding shaft grounding to their UL binder and then demonstrate adherence to the additional set of procedures required for installing shaft grounding inside of XP motors.

Motor repair shops with UL certification to work on XP motors and certification of their ability to add shaft grounding can “rework” any size explosion proof motor and then re-nameplate the motor as explosion proof. The drawing below was created by UL to show where the ring must be installed to comply.

The AEGIS® Shaft Voltage Tester™ is a CAT II/III digital oscilloscope that includes everything you need to test voltage levels on the spinning shaft of a motor — an oscilloscope with advanced functions, a probe with special conductive microfiber tips for exceptional shaft contact, a probe holder with a magnetic base, and a compact carrying case.


For some applications, an oscilloscope must be calibrated according to the requirements of a standards organization, like ISO or ANSI.  We now offer an AEGIS Tester™ that is ISO 17025 certified.

Part Number:  AEGIS-OSC-9100MB-W2-IC

For more information see our brochure or visit the AEGIS Tester product page.

aegis_sgr-grp-2016The “Greening” of America’s Buildings:  The growing “green” movement has led to a flood of new standards including the US Greens Building Councils Building Performance Initiative, the Green Building Initiative, and LEED — all aimed at increasing energy efficiency and sustainability. Challenged to reduce energy consumption and to document savings, America’s facilities managers are installing variable frequency drives (VFDs) in HVAC systems as one of the best ways of achieving such savings.


The Promise of VFDs:  VFDs reduce energy consumption by allowing motors to run less than full speed. When used to control air conditioning, air handling,
or pump motors, VFDs can yield energy savings of 20 ~ 30% or more by allowing motors to run at reduced speeds to compensate for changes in load.


The Need for Shaft Grounding on VFD-Driven Motors:  But, VFDs can damage the motors they control. They induce currents on motor shafts that discharge through the bearings, causing pitting, fluting, and catastrophic motor failure. Without bearing protection, any savings from the use of VFDs can be
quickly wiped out by the cost of replacing motors and by system downtime. To make HVAC systems sustainable as well as energy efficient, a reliable method of bearing protection is required.
Proven, Long-Term Bearing Protection:  By diverting bearing currents safely to ground, AEGIS® SGR Shaft Grounding Rings ensure the reliable, long-term operation of VFD driven motor systems, locking in energy savings and making these systems truly sustainable and truly green.

Select Motors with Factory Installed AEGIS from Baldor, WEG, Regal, TECO, Leeson and more

Select Motors with Factory Installed AEGIS from Baldor, WEG, Regal, TECO, Leeson and more

AEGIS® Shaft Voltage Tester™ Digital Oscilloscope to Test VFD-Controlled Motors for Damaging Shaft Voltages

Industrial motors controlled by variable frequency drives (VFDs) are at risk of electrical bearing damage. The new AEGIS® Shaft Voltage Tester™ Digital Oscilloscope makes it easier than ever to check in-service motors for damaging VFD-induced shaft voltages and head off bearing damage and costly unplanned equipment downtime. Read the rest of the article…