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.

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