Gap both rails and put feeders in both rails. Forget the "common rail" stuff if you plan to eventually go to DCC. As I mentioned in the DCC section, you can 'fake' the common rail part to hook up DC components simply by tying the feeders that would be the common rail together and run a single wire from that point to the cab(s).
For a small layout it doesn't make much difference - if there is only a single DCC booster it will never matter. But if you divide the layout into multiple power districts, or have more than one booster, common rail is a no-no. The posisble problem with common rail on even a small layout is typical layout diagrams show exactly ONE feeder for the common rail for the ENTIRE layout. Great, 20 blocks with feeders on the non-common side but one feeder on the other - can you say "voltage drop"?
If you have Andy's book then I assume you know what I mean by common rail wiring since it's in the book. The two feeders to each block is often called direct home wiring, dunno if that's the term Andy used or not.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
I would gap both rails and used double pole double throw toggle switches to switch both rails. This always works. The more sophisticated "common rail" system allows use of single pole toggle switches but it doesn't really matter. Both types of toggle switches cost about the same. There are a number of wiring blunders you can make on common rail that are hard to find and fix. Common rail doesn't work thru a reverse loop. It's harder to understand and trouble shoot. I would treat both rails the same, everywhere. Any where I gap or switch one rail, do the same with the other rail.
For DC operation, you want to be able to turn off track power on sidings and spurs so the express trains can use the main while the peddler freight waits on a sidetrack. If you have a double track main, you want each track to be a separate block, so you can run two trains at once.
When (if) you spend the money on DCC, the block toggles can be left in place and they even assist in trouble shooting. When you get a short on DCC, the DCC control box shuts down to protect itself leaving little clue as to where the problem is. With block toggle switches you can turn off blocks until the short goes away. That localizes the fault down to a single block, which is better than looking over the entire railroad for the short.
David Starr www.newsnorthwoods.blogspot.com
A practical addition to what has been said above - wire from a small terminal strip where the drops come through the subgrade (to the underside of the table) to larger terminal strips at the panel - and be sure to mark the terminals and document everything.
One common misconception about common rail is that there are no gaps in that rail. While it might be possible to have a humongously long single common rail section, that would create a troubleshooter's nightmare. I actually use common rail wiring for analog DC, but the sections are isolated and connected to the RCom bus at terminal strips - a slightly more sophisticated variant of Randy's, "Twist them all together." Using a common rail bus and SPDT switches gets you half way to, "Proper DCC," wiring while cutting the drop-to-panel wiring count to 1/2 + 1 as compared to, "Two wires per block."
The only thing about using a common rail bus is that your locomotive power has to come from two totally independent sources with no common connection other than that RCom bus on the low-voltage side of their internal transformers. With two operators, that is the ergonomically correct way to arrange locomotive controls if you are operating with either fixed power packs or one fixed and one walk-around.
Note that all of the above is predicated on setting up your DC circuits for only two operators. Unless you have a basement-filler and expect to host a group of operators, that's really all you need - and adding more controllers will make things much more complicated and expensive. Unless you have a really good reason to go there, don't.
Chuck (Modeling Central Japan in September, 1964 - analog DC, modified MZL system, common rail)
I'm going to take a somewhat contrary position...I used common rail wiring extensively when in DC.
I wired my currently layout for DC, with an eye toward my eventual DCC conversion. I gapped both rails at the crossovers between each main track, and each main track and the branches. For the blocks within each main or branch I gapped one rail.
Nick
Take a Ride on the Reading with the: Reading Company Technical & Historical Society http://www.readingrailroad.org/
By all means, get yourself a DCC wiring booklet. I happen to use Digitrax for my DCC layout. Once you decide on the brand of DCC, stick to it for all your DCC needs. The different companies are becoming more and more compatable with NMRA standards, but using one brand is recommended. Depending on the size of the layout, it should be be divided into "independent power districts" (with toggle switch "turn-off" capability for each district, and a means of locating the exact position of "shorts", within each district. I use the auto tail light method of pinpointing the location of the short. Preplan the location of reverse loops, wyes, and perhaps an electrically controlled bridge or round table. Use plastic insulated joiners on both branches of every switch which may eventually form a Wye of reverse loop. I solder a "jumper wire" across the plastic joiners. These make great places to solder the leads from "reverse loop modules", for DCC operation. Loops within loops require special consideration, as to the placement of reverse loop modules. The use of dpdt toggle switches, instad of automatic reverse loop modules, is not a good choice! Bob Hahn