Why do GFCIs keep tripping? I thought this outlet worked before?

As well known, ground fault circuit interrupters (GFCIs) are used to protect people from electric shock. Recently, a manufacturer installed variable speed drives (VSDs) in all their products. After receiving feedback from their customers, they realized that their products would only work when powered through some GFCI outlets but not work when powered through others. To investigate this problem, the authors purchased different types of commercially available GFCIs and tested each using the standard Electrical Fast Transient (EFT) test. The purpose of the EFT test was to simulate the emissions of a variable speed drive. Three out of eight GFCIs tested were found to trip at different voltage levels indicating that the EFT test could be useful to differentiate the performance of different types of GFCIs in terms of their ability to handle impulses from VSD products.