Reducing Induction Effects, Counter-EMF, and Stray Voltages in Low-Voltage Communication Wires.

One of the observations which amaze older people like me, is how high the frequencies have become, at which even household appliances such as USB Cables can communicate. In my youth and young adulthood, such things would not have been considered possible. And the surprise which this progress brings, comes more strongly to older people, who actually did know about Electronics.

There is a basic enemy to allowing communication at high speeds: Plain wire has linear inductance, which becomes significant at the higher speeds.

There is a basic methodology to reducing the unwanted effect: Actual signal-wires are often accompanied by a shield wire, which needs to be grounded or connected to zero, at both ends of a wire bundle.

The concept is quite simple. This shield wire acts as a kind of secondary winding, to a virtual transformer, of which the signal wire would be the primary winding. Whatever counter-EMF the signal wire would produce, would also need to exist along the length of the shield wire. But because the shield wire is grounded at both ends, the counter-EMF which the signal wire can produce is also greatly reduced, in comparison with what one would obtain, if the signal wire existed by itself. When current flows in one direction through the signal-wire, current also flows in the opposite direction through the shield wire. If that current could not flow, then the full linear inductance of the signal wire would seem to exist. Otherwise, not so.

Now I suppose that it would be nice if overhead wires that stretch geographical distances, could also be shielded as easily. But one fact which is highly disappointing is, that shielding / elimination of stray-power problems, is highly lacking in many practical situations. More specifically, power lines may often only seem to have real phase wires, but no neutral wire that runs parallel. Instead, what some Engineers do, is simply to sink a grounding electrode into the earth, at the receiving end of such an arrangement.

The problem with that is the fact, that Earth is not a perfect conductor, and was also never ‘meant to’ participate in Humans’ high-voltage circuitry.

(Updated 3/12/2019, 15h20 … )

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