EMC Question of the Week: October 7, 2019
In order for conducted coupling to occur, the source and victim circuits must be connected
- at one or more points
- at two or more points
- by a wire
- to an LISN
Answer
The correct answer is "b". Conducted (or common-impedance) coupling requires two or more conducting connections. One to bring the noise current from the source to the victim circuit, and one to return the noise current from the victim to the source. Any EMC coupling between two circuits that share only a single point of connection cannot be conducted coupling (and therefore must be electric-field, magnetic-field or radiation coupling).
Single-point grounding is an important technique for eliminating conducted coupling in certain situations. Unfortunately, this concept is often misapplied by people who confuse "ground" with "current-return." Having a single zero-volt reference for all circuits is often important. On the other hand, returning all currents to a single point is almost always a bad idea.
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