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Stray currents are a growing cause of premature bearing failure in electric motors. NTN explains the main protection options and how its MEGAOHM™ insulated bearing helps safeguard electrical applications.

Electric motors use almost half of the world’s electricity. To improve efficiency, European regulations now require higher motor efficiency classes (IE3, IE4 and IE5), which has made variable frequency drives (VFDs) standard on most motors. VFDs optimise performance and energy use, but they can also generate high-frequency currents that pass through the bearings.

This causes electrical erosion. Repeated discharges weaken the bearing surfaces, releasing metal particles that lead to pitting and cracking. The discharges also degrade the lubricant. The result is shorter bearing life, unexpected motor failures and higher maintenance costs.

Choosing the right protection

Etienne Vandamme, project manager and research and innovation specialist at NTN, outlines four main solutions. Conductive greases dissipate current but offer low, unstable protection, so they suit small motors and household appliances. Resin-insulated bearings work well up to 1,000 V in low-voltage motors but cannot operate above 120°C. Ceramic-insulated bearings provide very high insulation up to 3,000 V for AC motors, wind turbines and generators. Hybrid bearings offer complete insulation for electric vehicles, high-speed applications and aerospace.

Ceramic-coated bearings are the most widely used in industry, offering the best balance of performance and cost.

MEGAOHM™ from NTN

NTN’s MEGAOHM™ bearing features a thick alumina ceramic coating on the outer ring, providing electrical resistance up to 3,000 VDC, compared with 1,000 VDC for standard 100 µm solutions. It is available with steel or brass cages depending on motor size, and its dimensions are fully interchangeable with standard bearings, manufactured to ISO 492, DIN 620 and JIS 1514.

The bearing is recommended for AC/DC motors, servomotors, pumps, fans and compressors. Held in stock for fast delivery, it is designed for motor rewinding specialists and maintenance engineers who need a reliable solution quickly.

Find out more HERE.