I am curious as to what type of leakage test you are referring. Is this a chassis Hi-pot test for AC leakage to geround or something performed at a lower voltage? We do a Hi-pot from the AC mains connection to the metal chassis, but disconnect the AC/DC power supply to prevent damage to the power supply from the 2200VAC test voltage. The test is performed to meet CE Low Voltage Directive safety requirements. We trust the CE mark by the manufacturer on the power supply is sufficient to exclude the power supply itself from the high-voltage stress.
I'd second the idea of an article on grounding. I've been an engineer for 30 years, and just about every time I've worked with separate grounds in a system it has gone badly. Mostly I've worked on television cameras (commercial and medical), and keeping all the grounds tied together (usually through the chassis) has been consistently the most successful method for reliable results, both in EMI (which has always been a design concern) and signal integrity.
But I've also heard time and again that you should keep chassis and signal grounds separate, so it'd be really interesting to know what I've been doing wrong (or right) all these years. There must be a way to pass the EMI tests and avoid the ground noise horrors described in the article. You're never too old to learn!
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