@bmoran4 posted:2 rail generally uses variable DC voltage with polarity determining direction in conventional operation. For remote/command control, generally a fixed DC voltage is used with DCC. When going from 3 rail to 2, reverse loop/block wiring is also thrown into the mix (as opposite rails would meet up and short out). The above is true for just about all gauges.
One thing I'd add if you're looking at using some earlier MTH Proto-2 2-rail engines is to use relay-style polarity reversing for reverse loops as Proto-2 engines are polarity sensitive with respect to the DCS signal. There had been a discussion on this forum years ago regarding using DCS in a 2-rail context. If you're starting from scratch, I'd recommend DCC for command control, but a relay-based polarity switching method is still a good idea in case you want to run conventional DC.
