--- title: Zürich University for Applied Sciences on Motor Bearing Currents description: The Zürich University for Applied Sciences (ZHAW) studied how to reduce electrical bearing damage in small ac motors. Here's what they found. image: https://blog.est-aegis.com/hubfs/Imported_Blog_Media/motorbench-zhaw-204x300.png --- [![Electro Static Technology](https://blog.est-aegis.com/hubfs/raw_assets/public/public/images/electro-static-technology.svg "Electro Static Technology")](https://www.est-aegis.com/) [![Aegis](https://blog.est-aegis.com/hubfs/raw_assets/public/public/images/Aegis.svg "Aegis")](https://www.est-aegis.com/) - [+1 866-738-1857](tel:+1%20866-738-1857) - [Products](https://www.est-aegis.com/products/) - [AEGIS® SGR – for motors under 500 HP/375 kW](https://www.est-aegis.com/product/sgr/) - [AEGIS® uKIT – for common NEMA/IEC frame size](https://www.est-aegis.com/product/sgr-ukit/) - [AEGIS® RPPR – for reactor recirculating pumps](https://www.est-aegis.com/rppr-resources/) - [AEGIS® EV and EVO Rings - for electric vehicles](https://www.est-aegis.com/product/ev-evo-rings/) - [AEGIS® PRO Series – for motors over 300 HP/225 kW](https://www.est-aegis.com/product/pro-series/) - [Shaft Voltage Testing and Accessories](https://www.est-aegis.com/product/mounting-accessories/) - [Online Product Catalog](https://catalog.est-aegis.com/) - [AEGIS® 2-Year Extended Warranty](https://www.est-aegis.com/product/extended-warranty/) - [Applications](https://www.est-aegis.com/applications/) - [Electric Vehicle Solutions](https://www.est-aegis.com/applications/electric-vehicle-solutions/) - [Food & Beverage](https://www.est-aegis.com/applications/food-beverage/) - [HVAC](https://www.est-aegis.com/applications/hvac/) - [Industrial & Chemical](https://www.est-aegis.com/applications/industrial-chemical/) - [Other Industries](https://www.est-aegis.com/applications/other-industries/) - [Power Generation & Renewable Energy](https://www.est-aegis.com/applications/power-generation-renewable-energy/) - [Transportation](https://www.est-aegis.com/applications/transportation/) - [Water Treatment](https://www.est-aegis.com/applications/water-treatment/) - [Bearing Protection](https://www.est-aegis.com/bearing-protection/) - [Shaft Voltage & Bearing Currents](https://www.est-aegis.com/bearing-protection/shaft-voltage-and-bearing-currents/) - [Fluting & Bearing Inspection](https://www.est-aegis.com/bearing-protection/fluting-and-bearing-inspection/) - [Best Practices & Installation](https://www.est-aegis.com/bearing-protection/best-practices-and-installation/) - [Resources](https://www.est-aegis.com/resources/) - [AEGIS® Bearing Protection Handbook](https://www.est-aegis.com/resources/handbook/) - [IEEE-841, Hazardous Locations, & AEGIS®](https://info.est-aegis.com/technical-codes-and-ieee-841-standards) - [Recorded Webinars Library](https://www.est-aegis.com/resources/recorded-webinars/) - [Installation Instructions](https://www.est-aegis.com/resources/installation-instructions/) - [Videos](https://www.est-aegis.com/resources/videos/) - [Technical Papers](https://www.est-aegis.com/resources/technical-papers/) - [Case Studies](https://www.est-aegis.com/resources/case-studies/) - [Specifying AEGIS®](https://www.est-aegis.com/resources/specifying-aegis/) - [Request Training](https://www.est-aegis.com/resources/training/) - [Product Sheets](https://www.est-aegis.com/resources/product-sheets/) - [About](https://www.est-aegis.com/about/) - [News](https://blog.est-aegis.com/) - [Tradeshows](https://www.est-aegis.com/about/tradeshows/) - [Blog](https://blog.est-aegis.com/) - [Where to Buy](https://www.est-aegis.com/where-to-buy/) - [Distributors](https://www.est-aegis.com/where-to-buy/distributors?type=Distributor) - [Trained Installers](https://www.est-aegis.com/where-to-buy/installers?type=Installer) - [Explosion Proof Installers](https://www.est-aegis.com/where-to-buy/installers?type=Explosion%20Proof%20Installer) - [Motors & Seals with AEGIS® Installed](https://www.est-aegis.com/where-to-buy/oems-with-aegis/) [Contact Us](https://www.est-aegis.com/contact/) - [+1 866-738-1857](tel:+1%20866-738-1857) # Zürich University for Applied Sciences on Motor Bearing Currents [Home](https://www.est-aegis.com/) » [Blog](https://blog.est-aegis.com/) » Zürich University for Applied Sciences on Motor Bearing Currents [AEGIS](https://blog.est-aegis.com/author/estaegis) Apr 20, 2021 In 2017, the School of Engineering at Zurich University of Applied Sciences (ZHAW) began a long-term study of electrical bearing damage.  Whereas most prior research had focused on large motors on drives, this research focused on smaller motors. [![](https://blog.est-aegis.com/hs-fs/hubfs/Imported_Blog_Media/motorbench-zhaw-204x300.png?width=204&height=300&name=motorbench-zhaw-204x300.png)](https://blog.est-aegis.com/hubfs/Imported_Blog_Media/motorbench-zhaw.png?hsLang=en-us)This project was commissioned by the BFE, the Swiss Federal Bureau of Energy.  The research consisted, in part, in running 11 identical 2 hp (1.5 kW) motors on drives for 10 months, and then cutting and examining their bearings.  Each of the 11 motors was equipped with different types of protection (or lack thereof) against electrical bearing damage.  Among other options, these protective measures included specialized VFD cable, common mode chokes, insulated bearings, and AEGIS Shaft Grounding Rings. Before going into the test results, we should review the [three types of VFD-caused bearing current](https://blog.est-aegis.com/common-mode-filters-cant-prevent-all-electrical-bearing-damage/?hsLang=en-us).  EDM current, aka shaft voltage discharge or rotor discharge current, is a problem in motors of all sizes.  High-frequency circulating current is a problem in larger motors, over 100 hp/75 kW.  And rotor ground current is a problem in poorly grounded motors of all sizes. Because these were small motors, circulating current was not a problem.  The researchers found that both shaft grounding rings and insulating both bearings prevented damage from EDM and rotor ground current.  (Grounding the motor shaft alone would *not* protect coupled equipment's bearings from rotor ground current.)  Common mode chokes reduce rotor ground current but do not decrease EDM current - and can worsen it.  Likewise, improved grounding and special VFD cabling prevent rotor ground current but do not affect EDM current. |   | ![zEDM-zhaw](https://blog.est-aegis.com/hs-fs/hubfs/zEDM-zhaw.jpg?width=827&height=518&name=zEDM-zhaw.jpg)   |   | | --- | --- | --- | The EDM "risk number" for each of the 11 motors. (Low risk number is good.) The least at-risk motors are #1, with insulated bearings, & #2 with an AEGIS ring. The next two are at risk: #3 has a well grounded frame, and #4 and 5, a common mode choke. #6-11 have various levels of shaft and frame grounding. What is their final recommendation for preventing bearing currents in small machines?  EDM current can be mitigated by effective shaft grounding (such as AEGIS Shaft Grounding Rings) or two insulated/hybrid bearings.  The good high-frequency grounding of the motor frame can prevent rotor ground current. AEGIS Rings also come with a [2-year extended warranty](https://www.est-aegis.com/product/extended-warranty/) against bearing fluting damage. No other form of protection against VFD-caused bearing damage offers a warranty like this. [![2-Year Extended Warranty](https://no-cache.hubspot.com/cta/default/20974229/3b258d08-3058-4c7f-a866-2991b627f2e0.png)](https://cta-redirect.hubspot.com/cta/redirect/20974229/3b258d08-3058-4c7f-a866-2991b627f2e0) To learn more about AEGIS shaft grounding and best practices for electrical bearing protection, [sign up for a training](https://www.est-aegis.com/resources/training/). We offer monthly live training webinars, and we can also visit your facility to review your exact application. [![Sign Up For Training](https://no-cache.hubspot.com/cta/default/20974229/69dd56c7-bbd1-4ad0-ae5c-29de322039f0.png)](https://cta-redirect.hubspot.com/cta/redirect/20974229/69dd56c7-bbd1-4ad0-ae5c-29de322039f0)   [Motors on VFD](https://blog.est-aegis.com/tag/motors) ### Subscribe To Our Blog ## Read On ### [Three Types of Bearing Current: Mitigation](https://blog.est-aegis.com/three-types-of-bearing-current-mitigation?hsLang=en-us) ### [VFD Switching Frequency & Bearing Current](https://blog.est-aegis.com/vfd-switching-frequency-bearing-current?hsLang=en-us) At almost every Q&A session we hold, the question comes up: "Does VFD switching frequency affect... ### [Prevent Downtime with Electrical Bearing Protection](https://blog.est-aegis.com/prevent-downtime-with-electrical-bearing-protection?hsLang=en-us) More and more electric motors are being controlled by variable frequency drives (VFDs). VFDs offer... [![Electro Static Energy](https://blog.est-aegis.com/hubfs/raw_assets/public/public/images/logo-est-alt.svg) ![AEGIS](https://blog.est-aegis.com/hubfs/raw_assets/public/public/images/logo-aegis-alt.svg)](https://www.est-aegis.com) 31 Winterbrook Road Mechanic Falls, ME 04256 Phone: [+1 207-998-5140](tel:+1%20207-998-5140) Fax: [+1 207-998-5143](fax:+1%20207-998-5143) Contact Us: [Send Message](https://www.est-aegis.com/contact/) ## Subscribe to Our Emails - [Products](https://www.est-aegis.com/products/) - [AEGIS® SGR](https://www.est-aegis.com/product/sgr/) - [AEGIS® uKIT](https://www.est-aegis.com/product/sgr-ukit/) - [AEGIS® PRO Series](https://www.est-aegis.com/product/pro-series/) - [Testing & Accessories](https://www.est-aegis.com/product/mounting-accessories/) - [Custom Static Solutions](https://www.est-aegis.com/product/custom-static-solutions/) - [Product Catalog](https://catalog.est-aegis.com/) - [AEGIS® 2-Year Extended Warranty](https://www.est-aegis.com/product/extended-warranty/) - [Applications](https://www.est-aegis.com/applications/) - [Electric Vehicle Solutions](https://www.est-aegis.com/applications/electric-vehicle-solutions/) - [Food & Beverage](https://www.est-aegis.com/applications/food-beverage/) - [HVAC](https://www.est-aegis.com/applications/hvac/) - [Industrial & Chemical](https://www.est-aegis.com/applications/industrial-chemical/) - [Other](https://www.est-aegis.com/applications/other-industries/) - [Power Generation & Renewable Energy](https://www.est-aegis.com/applications/power-generation-renewable-energy/) - [Transportation](https://www.est-aegis.com/applications/transportation/) - [Water Treatment](https://www.est-aegis.com/applications/water-treatment/) - [Resources](https://www.est-aegis.com/resources/) - [Request a Training](https://www.est-aegis.com/contact/request-a-training/) - [AEGIS® Bearing Protection Handbook](https://www.est-aegis.com/resources/handbook/) - [Videos](https://www.est-aegis.com/resources/videos/) - [Technical Papers](https://www.est-aegis.com/resources/technical-papers/) - [Case Studies](https://www.est-aegis.com/resources/case-studies/) - [Specifying AEGIS®](https://www.est-aegis.com/resources/specifying-aegis/) - [Product Sheets](https://www.est-aegis.com/resources/product-sheets/) - - - Copyright 2022 Electro Static Technology. All rights reserved. Made in America. - [Privacy Policy](https://www.est-aegis.com/privacy-policy/) - [Terms and Conditions](https://www.est-aegis.com/terms-and-conditions/) - [Sitemap](https://www.est-aegis.com/sitemap/)