I have searched the archives for the answer to this question (I’m sure it is in the archives somewhere, but I ran out of patience & decided to post) — given new track (in my case Gargraves SS, indoor use) is there any reason to run a bus wire for the ground rail? Layout is 16 x 20’, conventional engines & operation. Thanks! Zephyrx
Yes, for fail-safe operation you need a “common return” conductor back to the “U” terminal from one or both of the outside rails. If you have wooden ties you may want to attach a conductor to both outside rails–depends on how you operate.
Although the term “ground” is frequently and incorrectly used there is no ground on an ogauge railpower system. Only Hot and Common conductors**.**
Thanks A&YRy - Follow-up : Will maybe 1 or 2 feed wires suffice for the “common” rail, or should they be included with each “hot” feeder? (if so, why?). Zephryx
A 16-by-20-foot layout probably has at most 70 feet of track in the largest loop. The track is (very roughly) equivalent in resistance to 16 AWG copper wire, which has a resistivity of 4 milliohms per foot. Therefore, the resistance to the farthest part of the layout is about 70 milliohms. If a train draws 5 amperes, the voltage drop is only 350 millivolts, which is negligible.
So make your track joints tight (or soldered), connect the outside rails together wherever your track plan brings tracks close to each other, and connect your transformer’s common to the most convenient and closest outside rail at one point. (The common is the U terminal on multiple-output postwar transformers, but not on single-output transformers.)
(Use wire heavy enough to safely carry the greatest current that your transformer can supply, regardless of how little current your trains draw.)
In case you might be wondering, the “voltage drop” between a transformer and a train isn’t all in the center rail and the wire leading to it. A substantial portion of it is also in the outside rails and their wiring, which are every bit as much in series between the transformer and the train as the center rail and its wiring. (Perhaps it should be called a “voltage rise”. But, in any case, it contributes to making the voltage at the train less than it should be.) Of course, there are two outside rails, which halves the outside-rail voltage drop. And, if the outside rails are connected all around the loop as the center rails might not be, the farthest point on the loop is distant from the transformer by only half the loop perimeter and is fed through two paths. That’s another factor of four reduction in the outside-rail resistance. So the voltage drop due to the outside rails is probably significantly less than that in the center rails and their wiring. My advice to cross-connect the outside rails of nearby tracks is also aimed at further reducing this drop. With all these things in place together, you may see why I doubt that multiple feeds to the outside rails will make a noticeable difference.
The second outer rail likely is not in the circuit with the original poster’s Gargraves track, so it wouldn’t half the voltage drop in his case. With the stainless rails, the only additional power feeds may be near switches or blocks that may have insulating pins on the outer rail that is powered. That could make the current take the long way around the loop of track to the transformer instead of a closer route.
J White
Hard to tell Bob if connecting both outside rails to the return conductor is important. My practice has been to follow Lionel’s initial advice in their Trainmaster Command Control handbook regarding wiring a layout for TMCC-----common conductor to both outside rails.
IR Drop in low voltage circuits, in often casually wired ones, can be a unwelcome factor as I learned long ago in Navy Landing Boats. Calculations rarely hit the mark.
If the outside rails are not connected together, they should be, here and there. Usually there is at least one return path through a turnout. If the outside rails are connected together, whether incidentally in the turnout or deliberately near the turnout, a short distance of one rail through the foot or so of the turnout is not significant, although even that is easily avoided by a short jumper around the turnout. The principle that I’m trying to get across is that it is usually easy to create multiple paths in the outside rails, to the extent of reducing resistance by a factor of eight in a simple loop (half the distance, two rails in each of two directions) and quite a bit more if cross-connections among multiple loops and other tracks are exploited.
If engineering assumptions are unrealistic, then engineering calculations may well fail to solve the problem. But that is not a good reason to abandon engineering in favor of the expensive trial and error approach once used, for example, to build European cathedrals. Those that still stand do so not because of brilliant or competent engineering, or engineering of any kind. They are simply the minority that didn’t fall down on their creators.
In the case of feeders for outside rails on a small layout, the penalty for trial and error is not death and decades of labor, but just the small effort to put in a few wires. Since the wires are usually about as easy to add after the fact as before, an analysis that suggests they are unneeded, by about an order of magnitude, seems to me enough reason to take a small chance on not installing them. In any case, he should know that he is free to disregard the answers to his question.
Thanks for the explanation guys. I believe I’m “good to go” now.
Lionelsoni - Your reference to a “ring main” was both instructive & interesting. Toy trains aside, it reinforces a notion I acquired as a teenager when I tried to work on a friend’s MG — The Brits have some unique ideas about wiring.
Zephryx