Colorado Front Range Railroad: http://www.coloradofrontrangerr.com/
The bridge rails and the lead rails have to be air-gapped for mechanical as well as electrical reasons, unless your workmanship rivals that of Rolls Royce for precision. I would lay the lead and stall tracks AFTER the turntable is in and de-bugged, with about a 1/16 inch (in HO) gap and something like a spikehead or several soldered to every rail to prevent creep.
In theory, a stereo plug would work for both an axle and an electrical connector - but, how are you planning to power the turntable. Applying torque to the plastic sleeve of the plug could tend to unscrew it from the pin. Also, since the stereo jack gives very little anti-tilt capability, the bridge would have to ride on the carrier rails around the edges of the pit. Either that, or carry the bridge on a more serious bearing and use slip rings on the central pedestal for power transmission. (Since you specified DCC, the old analog DC trick of using a split carrier rail would confuse your decoder when the power is interrupted, which it will be as the table turns.)
I, personally, use analog DC - and bicycle wheel hubs and axles for center bearings.
Chuck (modeling Central Japan in September 1964 - one turntable operating, one to be built)
Jim, that is my understanding, as well. Any reversing loop, of which the TT's tracks are one, must be physically isolated from the rest of the layout. The air gap you mention is just the ticket, although you need to take some care to ensure there is not too large a gap between the approach rails to the bridge and the bridge rails. Making the engine wobble because of slight misalignment in azimuth is one thing, but making it wobble because of misalignment due to height or an overly large gap is going to look sloppy.
The turntable I have, the 90' Walthers one, has two brass rings on the bridge's axle, or pivot, that are separated by a plastic spacer to keep them in position and apart. The axle is hollow, so small wires soldered to the brass rings can be fed up through the axle, up through the bridge ties, and nestled and soldered against the rails. This part of my kit has worked flawlessly. The phone jack idea has been mentioned here before, and I believe Randy Rinker cautioned about the type because one of them is not suitable. Maybe he will respond soon and remind me which is the one.
Edit- I erred in stating that the wires are soldered to the brass slip rings. They are not. They are connected to copper wipers that are held against the brass rings from their separate moorings on the sidewall of the motor housing. The copper wipers are placed in such a way that they are under tension, like leaf springs, against the brass rings. Inside the rings, on their inner surfaces, is where two more fine insulated wires are run up the hollow pivot and soldered at the far ends to their respective rails. Sorry for the confusion.
This is how I wired mine. A main bus to the roundhouse area. I connected the bus wires to a terminal plate. Then I wired seperate feeders to each track in the roundhouse from the terminal plate. Lastly I ran feeder wires to the turntable rails themselves from the terminal. Before the wiring gets to the turntable I wired in an autoreverser. Yes you must have a gap between the turntable rails and the rails going into the roundhouse. If they touch the system will either sense a short and shut down or the reverser will keep tripping. Just enough gap so that the turntable can move has been sufficient for me. Never expirienced an arc across the gap so far.
As for power to the turntable to turn it, I haven't gone to DCC with that. I power it by using an old power pack wired to the turntable motor.
I did not do this but I've seen where some people also have a switch for the roundhouse tracks so they can turn off power to the roundhouse thereby taking the parked engines off line to reduce power consumption or prevent sound equipped engines from making noise when you dont want them to.