I would like to use a bus wire when extending a what is basically an oval. The question is, can I run two pairs of wires from a center power source with one set going east and the other set going west then attach feeders at any spot on the oval? Keeping all "red" on one side rail and all "black" on the other side rail protecting polarity. I will be running DC or DCC by use of a routing switch from the two different power sources to the bus wires. Thanks in advance.
Yes. It is very common for larger layouts, even ovals, to have the power feed centrally located. As you note, the polarity is what you have to watch.
Having the command station in the middle of the bus, with a big "T" junction and some feeders east and some feeders west is perfectly fine, for either DC or DCC. Most DCC systems have a length limit, so make sure no feeder is further than 'x' feet from the command station (where 'x' depends on your brand). And some DCC systems do not like "loops" in the bus - so it is a good idea not to connect "east" and "west" on the far side of the oval. (In short, each feeder from a rail should only have one path along the bus back to the command station; if there are multiple paths, your locos may behave.. "weird". I wonder if newer systems are better? )
If you are going with DCC consider adding a termination resistor & capacitor. This has been reported to reduced reflection on the bus wires, I haven't tested this though but a lot of people have.
Unless you are running VERY long busses (well over 30 feet each way) the terminating circuit has very little effect. At the more reasonable distances seen on most home layouts, having ANY kind of load on the bus (including even one locomotive) will serve the same purpose... I actually looked into selling a terminating circuit that one could just plug into the end of the wire, and the deeper I looked into it the more convinced I became it was useless under all but the most extreme circumstances. Much better to just keep the bus lengths in the range of 30 feet or less and just don't worry about it. Even with very large home or club layouts the smarter move is to subdivide into power districts where the buses turn out to be shorter, rather than powering the whole thing with very long bus lines. Although power districting should be done more by load than by distance...
Thank you for all the replies, sounds like I should be okay. My layout is shown below and it is just a tad over 25' side to side. The power supply will be just to the right of the widest portion at left so the longest bus will be 17' from that point and 7' going left. Outside rails will be red feeds about every two or three feet with the inside rails the black feeds with same spacing. All sidings will use #6 Kato power routing turnouts so I plan to have one feed at the lead in and use the turnout for power control.
Is the bus going to follow the rails in a semi-loop, or just straight from the booster to the end of the table? If it's in a semi-loop then your runs will be much more than 17 and 7 feet... more like 40 feet and 16 feet or more. it's the length of the wire that matters, not the straight-line distance from the booster. You could still make it work if you run the bus wires straight down the center of the loop in a "T" shape with feeder wires branching off to reach the tracks, like a tree rather than a loop. If you wre already thinking of a straight line "tree" design, well, nevermind...
