I'm looking for information regarding twisted triad vs twisted pair cable use with RS-485, especially in applications with long distances outdoors.
With twisted pair like Belden 3105DB, the drain is connected to the shield, and this is the shared ground reference between RS-485 transceivers. Or do I have a misunderstanding of twisted-pair RS-485, and the drain should not be used as the reference ground?
Given that the purpose of the cable shielding is to reduce EMF coupling, would it not be better to isolate the reference ground with a twisted-triad, like Belden 3106A? Are there any downsides to using a twisted-triad over a twisted pair?
I've seen recommendations for using using a double twisted pair, but is this a recommendation over a twisted triad? I don't understand why this would be—is it to avoid capacitance between the reference ground and the data lines?