As part of its ongoing virtual seminar series, Hi-Speed Industrial Service recently hosted a virtual webinar on electric motor core testing, presented by Blake Parker, Director of Shop Operations. During the presentation, Blake reviewed factors that are critical to effective core testing and repair. He also explored all aspects of electric motor core testing, including when it should be done and what happens if it fails.

Cores are made of non-oriented steel to provide a uniform magnetic property in any direction of the material. Stator coreplates can go bad as a result of thermal degradation or from physical damage from rotor drags or improper disassembly or improper winding removal. When testing electric motor cores, one typically checks the insulation integrity between laminations and the overall efficiency of the machine. This is done by inducing current into the core, typically at 85,000 lines of flux, measuring the number of watts lost per pound, and checking for hot spots.

Blake noted the importance of testing cores before and after burnouts as well as ensuring the burnout oven doesn’t exceed 750 degrees Fahrenheit. Testing can be performed either by a commercial core tester or through multiple wraps of wire through the core that are calculated based on industry standards. He also suggested infrared hotspot testing be done to provide a visual representation of shortened laminations. Ideally, images should be taken 0 minutes, 10 minutes and 20 minutes into the test comparing the temperature differential at every area of the core. Mapping the laminations prior to removal as well as after restacking is critical to a successful core repair.

After the presentation, Blake held an interactive discussion with attendees.

Hi-Speed Industrial Service is dedicated to continually providing industry experience and knowledge-based learning opportunities for customers, team members, peer companies, service providers and the public. For more information on Hi-Speed or its next educational seminar, visit

Founded in 1946, Hi-Speed Industrial Service specializes in repair and sales of electro-mechanical equipment (electric motors, pumps, gearboxes, fans and blowers); service, repair and construction of overhead hoist and crane systems; technology-enhanced predictive and preventative maintenance services; and round-the-clock availability. With locations in Millington and Little Rock, Hi-Speed provides services to clients throughout the southeast. For more information, visit or call 800-713-0103.