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Re: No, No, No...

>But now I say a floating differential is a disaster waiting to happen when you try to couple that to a grounded secondary. You need a drain to ground for differential signals everywhere somehow, even if the resistance is large.

Where would a high common mode voltage come from? A conductor doesn't acquire a charge merely because it's insulated from ground. Also, consider that common mode impedances in these circuits aren't all that great. They do provide a path to ground that is significant in the context of static buildup.

>I bet the phone company uses center-tapped points to Earth ground along the way. That keeps the static down for the reasons I stated.

I don't know much about telco wiring. If I had to guess, I'd say it's shielded.

>And I still contend you can do well with twisted pairs in unbalanced circuits, most of the time.

I think we frequently do things not because they produce a discernible benefit, but because they aren't demonstrably detrimental. It's likely the joint product of superstition and our love of gambling. In any event, twisted pair works on the theory that if the currents in the two wires are equal and opposite, field cancellation will reduce radiation from (and incursion into) the two conductors. When one of the conductors is grounded, though, that doesn't happen. The grounded conductor might provide a certain degree of shielding, but I don't see how it could be very effective.

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