Posted by John Davis on April 19, 2023 at 01:47:18.

In Reply to: Lesson About Good Grounding posted by Dave Childs on April 18, 2023 at 23:10:15.

A good story, Dave, and one we all need to think about from time to time. (Especially also during spring storm season. Lightning currents are fundamentally the same thing as very strong bursts of RF.) At any frequency above DC, "grounding" is a relative term. The earth is not a giant "noise sink" in the first place, nor is anything connected to it necessarily at the same potential as anything else that's connected to it at any given instant...especially if they share a common conductive path of several feet on the way to the ground point. A few microhenries of mutual inductance shared between two grounded conductors can produce a very effective noise coupling network between them. (Complicating matters in the case of lightning protection, the NEC requires one common ground point, but all grounds going to that point need to take separate paths to get there. It's a challenge to meet those criteria without creating new loops between QRM on power wiring and the grounding needed to protect against strikes to a tower, for instance.)

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