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A formal compliance test is designed to answer a specific question: Can a product meet the requirements of a standard or certification when tested in a defined way? But while the test can determine whether a product passes or fails, it’s not always optimized to explain why a failure occurred.

That distinction matters when it comes to electromagnetic compatibility (EMC) because many of the underlying issues start out as ordinary hardware interactions in, on, or around the PCB. These include return currents taking an unintended path, a cable carrying common-mode current, a power converter exciting an enclosure resonance, or a wireless subsystem changing the current distribution of the finished product.