Monthly Archives: December 2016

Most companies are constantly looking for ways to save energy.  It’s a quest that never ends.  But it does not have to be tackled all at once.  Older motors — even those that were customized for a particular system/application or those no longer in production — can be made more energy efficient through the use of variable frequency drives (VFDs).  VFDs provide a simple, cost-effective means of controlling a motor’s speed or torque by varying the power output to the motor.  In doing so, they can not only improve process control, they save energy.

And if the output of the motor is somehow restricted through the use of dampers or other throttling mechanisms, the use of a VFD can save even more in energy costs by precisely matching capacity to varying demand and eliminating the needless waste of energy.

If a new motor would be a logical replacement for an older motor, the potential for energy savings is greater still.  New NEMA Premium motors offer increased efficiencies of 5-7% for smaller motors (10 HP or less).  So replacing an older standard efficiency motor with a new NEMA Premium efficiency motor controlled by a VFD could yield impressive energy savings.

But controlling a motor with a VFD can also shorten the motor’s life.  EDM pitting, frosting, and flutingVFDs create damaging voltages on the shafts of the motors they control.  Without proven, long-term shaft grounding, these voltages can discharge through motor bearings, causing electrical discharge machining in the form of pitting (tiny fusion craters in metal surfaces), frosting (widespread pitting), fluting (washboard-like ridge in the race wall), and complete bearing failure — in as little as 3 months!  And the costs of bearing or motor replacement and unplanned downtime can easily wipe out any energy savings from the use of VFDs.AEGIS Shaft Grounding Rings

AEGIS® Shaft Grounding Rings combine direct contact and proprietary non-contact technology to provide superior  grounding and protection of motor bearings for their full L-10 life.  AEGIS® Rings channel these damaging voltage discharges away from bearings and safely to ground, protecting VFD-driven motors and the energy savings they generate.

You can easily install AEGIS® Rings yourself on any motor (even those with shaft shoulders, An array of motors with AEGIS factory-installedslingers, or other end bell protrusions), or have your local motor repair shop install them.  But the simplest way to prevent VFD-induced bearing damage is to purchase a new motor with AEGIS® Rings factory-installed from the manufacturer.  In fact, motors factory-equipped with AEGIS® Rings are offered by most major motor manufacturers.

So, if you are working on making your building, systems, or processes more energy-efficient, remember you don’t have to replace all of your motors, all at once.  You can replace older, less efficient motors (as they wear out) with new VFD-controlled NEMA Premium motors equipped with AEGIS®  Shaft Grounding Rings.

For more information on how VFDs can damage motor bearings, click here.

For more information on AEGIS® Ring Universal Mounting Kits, click here.

For more information on how AEGIS® Rings protect VFD-driven motors, click here.

For a list of manufacturers that offer motors with AEGIS® Rings factory-installed, click 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.

It Just Got Easier to Specify Shaft Grounding for VFD-fed Motors

AEGIS® Shaft Grounding Rings are frequently specified as protection against bearing current damage in motors fed by inverter drives.  And now it’s even easier to call for shaft grounding with this master spec for CSI Division 23 05 13, Common Motor Requirements for HVAC Motors, with AEGIS® best practices added.

CSI Div 23 05 13 with shaft grounding best practices added

An excerpt of Div 23 05 13 with added provisions for shaft grounding rings on VFD-fed motors.

Variable frequency drives are widely specified in HVAC applications for energy savings.  But VFDs produce capacitively coupled shaft voltages on the motors they control.  This shaft voltage can discharge through the motor bearings, leading to premature failure.  Grounding the motor shaft with an AEGIS® ring bleeds off shaft voltage before it builds up enough to discharge through bearings.

For more engineering resources, including the list of major manufacturers’ motors with AEGIS rings factory-installed, please see our specifications page.

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.

Commissioning agents ensure that the plans of the architects and engineers who designed buildings, systems, or processes are executed as intended and that their concerns are addressed before structures or systems are put into use. These professionals spend most of their time reviewing actual structures or systems to verify that they have been built or implemented as designed.  But savvy commissioning agents also take the initiative to point out potential shortcomings in designs and explain the consequences of these shortcomings… before

any oversights or omissions can result in expensive repairs or lost revenue for the building owner.

Many of the recommendations commissioning agents make are obvious — items shown in plans that were not installed or were installed incorrectly.  Others are not so obvious… such as motors controlled by variable frequency drives (VFDs) that have destructive shaft voltages but are not protected against electrical bearing damage.

VFDs create harmful voltages on the shafts of the motors they control — voltages that can discharge through motor bearings, destroying them and costing owners huge sums in repairs and lost production or revenue.

Testing for Shaft Voltage at Commissioning

A commissioning agent tests a VFD-fed motor for the presence of shaft voltage.

The best time to check motors to see if they are vulnerable to electric bearing damage is during the commissioning process.  By taking shaft voltage readings from the spinning shafts of VFD-controlled motors, a commissioning agent would see immediately whether the motor is protected with shaft grounding or not.

Motors with effective shaft grounding — such as ones with AEGIS® Shaft Grounding Rings installed — exhibit a virtually flat waveform, indicating a continual discharge of shaft voltage at levels too low to cause bearing damage.  Unprotected motors, on the other hand, exhibit a build up of voltage on the motor shaft to high levels, often 10-40 volts peak, followed by sudden violent discharges.  These discharges blast fusion craters or pits into the metal bearing surfaces.  Left unchecked, these discharges can lead to pitting, frosting (widespread pitting), fluting (washboard-like ridges on the bearing race), bearing grease degradation, and complete bearing failure — often in as few as 3 months!

The savings from preventing such damage can more than offset the cost of hiring a contractor to retrofit AEGIS® Bearing Protection Rings onto motors. Consider the following:

  • Most motor bearings are designed to last for 100,000 hours, but motors controlled by VFDs can fail in as few as 720 hours of operation.
  • When a large HVAC contractor ignored a specification that called for the installation of AEGIS® Bearing Protection Rings on all motors, the commissioning agent pointed out the omission to the building owner.  The job involved 300 motors, and the contractor was forced to remedy the problem at a cost of $200,000!
  • Motor failures caused by VFD-produced shaft voltage result in hundreds of thousands of hours of unplanned downtime each year in the US alone.  In addition, these failures reduce the performance and mean time between failure of the OEM systems in which they are used.
  • An HVAC contractor recently reported that, of the VFD-controlled 30-60 HP vane axial fan motors he installed in a large building project, all failed within a year (two within 6 months).  Repair costs totaled more than $110,000.
  • Several large pulp and paper companies surveyed noted that the VFD-controlled AC motors used in their plants typically fail within 6 months due to bearing damage.
  • After testing AEGIS® Rings on a VFD-controlled 50 HP “problem” fan motor — a motor that had suffered bearing failure 3 times — the engineering firm hired to test and tune the VFDs at the Time & Life Building in New York recommended installing AEGIS® Rings on all 240 HVAC system motors in the building.
The oscilloscope shows a bearing discharge on this motor without shaft grounding.

On this motor without shaft grounding, the AEGIS® Shaft Voltage Tester™ detects shaft voltage discharging through a bearing.

The best way to check for VFD-produced shaft voltages is to use an oscilloscope specifically designed to take such readings. The AEGIS® Shaft Voltage Tester™ Digital Oscilloscope is specially designed and configured to take accurate voltage readings from the spinning shafts of motors. It comes complete with a special conductive microfiber-tipped probe, a probe holder with magnetic base, and a compact carrying case.  The conductive microfiber probe tip provides exceptional electrical contact with the motor shaft.  It is made from the same highly conductive microfibers as the brushes of AEGIS® Shaft Grounding Rings.

If the motor specifications call for shaft grounding, a visual inspection of the motor may not be enough to verify that AEGIS® Shaft Grounding Rings were installed.  Since a large and growing number of motor manufacturers now offer motors with AEGIS® Rings factory-installed inside the motor, shaft voltage testing is needed to verify that motors are protected – especially if the AEGIS Installed label is not visible.  If readings indicate continuous low-level shaft voltage discharges, then the commissioning agent can feel confident that the AEGIS® Rings were, in fact, installed.

If the motor specifications call for shaft grounding, a visual inspection of the motor may not be enough to verify that AEGIS® Shaft Grounding Rings were installed.  Since a large and growing number of motor manufacturers now offer motors with AEGIS® Rings factory-installed inside the motor, shaft voltage testing is needed to verify that motors are protected – especially if the AEGIS Installed label is not visible.  If readings indicate continuous low-level shaft voltage discharges, then the commissioning agent can feel confident that the AEGIS® Rings were, in fact, installed.


Here is the same motor from above, now with an AEGIS® uKIT installed.  The shaft voltage has dropped to near zero.

If design specifications do not call for shaft grounding on motors, the commissioning agent can prove his value by recommending that motors be retrofitted with uKITs — AEGIS® Rings with universl mounting brackets.  AEGIS® uKITs were designed for fast, easy field installation around the shafts of coupled motors, and can accommodate shaft shoulders, slingers, and other end bell protrusions.

By making such a recommendation, the commissioning agent can help the building owner save the time, hassle, and expense of trying to fix a building or process problem… before it becomes a problem.

For more information on specifying bearing protection, click here.

For more information on testing motors to ensure they are protected against damaging VFD-induced bearing currents, click here.

For more information on the AEGIS® Shaft Voltage Tester, click here.