People who work with electric motors know that a sound stator core is the foundation of a good motor winding. Don't they? Or do they just take it for granted that the core has been properly checked? The stator core can appear to have a passive role that may lead some to assume that they do not require maintenance. Maybe we should look again. Look closely at a stator with the rotor removed and you'll see that the stator consists of laminations of metal plate which are separated by thin layers of insulation. Over time, these laminations can fail due to friction and other causes. And when these laminations fail, you get hot spots in the stator core. These hot spots can cause higher levels of heat and current imbalances measured as power losses in the stator. Hot spots can also lead to premature failure of the winding. So if you put a new winding into a stator core with failed lamination, it's like building a house on wet sand. It's doomed to failure. Fortunately, there are good procedures and guidelines in place to ensure this doesn't happen. The two commonly used core loss test standards are ESA AR100 and IEEE 432. Core loss testing should be conducted with enough time to allow the core to come up to temperature. Hot spots will usually develop in 10 to 20 minutes. A thermographic camera can identify and record these hot spots. Those exceeding 10 degrees centigrade above the average must be cleared regardless of the overall test results. Those test results are compared to the ESA database, which specifies that the core loss should be 1 to 6 watts per pound depending on lamination material. Tests are to be conducted before burnout and after stripping of the winding to ensure the core loss and iron temperature did not increase beyond the ESA standard. Your test report should include not only the results of the test, but also the job, motor name plate data, core dimensions, and the test parameters. Finally, it's a good idea to visit your repair shop to ensure their repair practices conform to these standards. Ask which testing standards they use. Look for written procedures. Ask to see actual test report data, including images from their thermal cameras. Doing so will assure you of solid state-or-course and better outcomes with your motor repair program. To learn more about this or other services we offer, visit us at ecoonline.com