I know you are missing my point. It doesn’t matter. You understand common rail and so do I. Common rail would have been more accurately named “control rail” since it is the electrical control of the blocks by isolating gaps in only the one rail that makes it a common rail “system”. Electrically, a common rail is a rail powered with one electrical source for its entire length. The return rail is akso a common rail if it meets that definition.
My point is that even double isolated blocks will be common rail unless you also switch power on and off to both rails (and of course use reverse polarity swit
You have to have at least two power packs to have a “common rail” layout.
A layout with a single power pack and isolated sections that can be turned on and off is not a “common rail” layout - you could call it that if you want, but in accepted model railroading parlance that is not correct. “Common rail” specifically refers to a method of wiring cab control where you have more than one cab (or power pack), and you have a common connection both between the cabs and one rail of the layout.
One thing that is confussing for some is that with common rail wiring you do not have to have the “+” of one cab wired to the “+” of the other. This means that you can switch directions of the cabs independently, so with a properly wired common rail layout you have independent control of speed and direction of the blocks. A “reversing section” on a common rail layout refers to a section of track where the “A” and “B” rails swap, such as a reversing loop or wye. These are the sections that need to be double isolated - not to give directional control of the trains but to prevent the “A” and “B” rails from shorting out to each other. These sections are actually still common rail, but you have to be able to switch witch rail is the common rail depending on which end of the section you are traversing.
I am a DCC user, so I have no skin in this game. But, when the thread started out, I tried to follow along to see if I could learn something about DC block wiring and common rail.
But, at this point, this thread has become useless because of so many contradictory statements. Somebody must be right, and somebody must be wrong. Is there any way to sort this all out in order to salvage this thread?
I just meant that in the reversing section, one of the rails is still going to be electrically common with the “common” rail of the rest of the layout although you have to be able switch which rail that is.
Not necessarily. “Common rail” does not have a fixed definition. Atlas Complete Wiring book describes common rail as a system with only one rail being gapped for electrical control. That allows two or more cabs to be conveniently connected without doubling up all the block wiring but only blocks are needed to create a common rail system. One powerpack will do. As is commonly accepted.
greg, I cannot believe that it is not obvious to you. The thread is littered with one guy saying this is fact and I am right, while the next guy says you are wrong and I am right. No, I am right and you are wrong.
Read back through the thread, and you will see what I am talking about. Who is to decide who is right and who is wrong? It renders the thread useless in my opinion.
Oh well, I give up. I don’t care anyhow because I am a DCC user. But I always thought that Common Rail was a well defined method of wiring as opposed to two rail wiring.
Common rail is just what its name says, there is one rail common through out the layout. In DCC both rails are common. The reason I don’t like or use common rail is it ties the direction of the DC locomotives locomotive to the same direction.
By using two separate power packs one can operate a DC locomotive in each direction but that requires one power pack to be connected positive to negative on the common rail.
I prefer to individually control the track polarity for each block individually, in both DC and DCC modes.
Back when I was learning two rail power vs. Lionel three rail I decided it was easier to switch both rails when controlling my layout. Even as a teenager connecting the positive terminal of one power pack to the negative of the second power pack didn’t sound like the way to operate two trains.
That was a decision of an early teenager and after 49 years and 10 months working in the electronics field nothing change even a little bit.
Like I said it’s strictly my preference to switch both rails rather than take a chance of crossing the voltages of two power packs. I like the no brainer approach.
It is, at least for the 35+ years I’ve been model railroading every discussion of common rail wiring I’ve seen has refered to the same thing. “Common rail” wiring refers to a method of wiring a layout for multiple cab control where one rail and one terminal of each cab is wired to a common point. It doesn’t refer to the number of feeders, the common rail can have one or a hundred and more, it’s still “common rail wiring” if those feeders all tie into the same common point with the cabs. A single cab DC layout is not “common rail” wiring. Sure there is a common left rail and a common right rail, so some people may call that a common rail layout, but without having one of the rails tied into a common connection between two or more cabs, it is not “common rail” wiring as generally understood in model railroading parlance. Even if that single cab layout has multiple blocks that can be switched on or off through a single pole switch, it still would not generally be considered a “common rail” layout. What distinguishes “common rail” wiring is that common connection between the cabs.
I just quoted what Atlas calls common rail in Chapter 3. They even have a diagram of a simple oval with one power pack, figure 3-1. You have to move on to Chapter 4 before Atlas adds a second Cab (powerpack). So, clearly, there is not a commonly accepted definition of common rail.
The Atlas 220 Controller is designed to work with common rail and allows polarity to be reversed for Cab A relative to Cab B, each Cab is given its own reversing switch and the powerpack reversing switches are not used.
Atlas diagram shows all the positive powerpack terminals connected to the same polarity and only the negative terminals go to the control rails. Or maybe the opposite since DC doesn’t care which way the current flows around the circuit. Atlas doesn’t label their diagrams with positive and negative until they start discussing reversing sections when current direction relative to the rest of the layout becomes important.
I don’t have the Atlas book, so I’ll take your word for it. As I said, every discussion I’ve seen has been about mutliple cab control, but that may just be because when someone has a question about common rail wiring that’s usually what they are wanting to do. Allowing for that it’s still a far cry from “all DC layouts are essentially common rail.”
The reason the Atlas 220 Controller has direction switches for the cabs is because with a reversing section you want to be able to reverse the cabs separately from the reversing section. If you were to use the power pack reversing switch, to traverse a loop you have to stop the train in the loop, throw the power pack reversing switch and the loop reversing switch, and then you can proceed out the other end. With the 220 controller you can throw the cab reversing switch while the train is in the loop and proceed through the loop without stopping. Without a reversing section you do not need the 220 controller and are free to use the power pack reversing switches.
there’s no reason the 220 couldn’t be used on a non-common rail layout. they are designed to plug into atlas 215 modules
there’s no need to reverse the polarity relative to the other cab. there is a need to independently control the polarity of both the reversing section and mainline
the powerpack reversing switch can certainly be used on both the mainline and reversing sections
perhaps you can explain what is wrong with the Atlas wiring using the following diagram we can all see
I’ve been staying out of these DC wiring threads because they are full of questionable or hard to understand advice and I don’t have the time to sort them out.
But first off, I would never recomment anyone use the Atlas system…
Second, the power pack reversing switches can be used as a “local direction switch” for the cab in question, but it is not really the best approach.
By only using the separate reversing switches established for the mainline and reverse loops, you can establish a protocal where the direction switches are always in the same position relative to the actual direction of travel, best defined as east/west on the main, and clockwise/counter clockwise in reverse loops.
Every time you change the power pack direction switch, you reverse this whole protocal changing everything down stream. Very confusing at best.
As an example, on my DC powered layout I use Aristo wireless throttles. The layout is designed and wired such that if you push the left direction button on the throttle, the train ALWAYS moves to you visual left, etc.
My reverse loops (of which there are just one loop, one wye, and one turntable) are wired in a semiautomatic fashion which maintains this directional continuity.
My entire layout is designed such that you are always viewing the trains as if you are facing north, left is west, right is east.
This is a distinct advantage for helping operators understand the layout, be they DC or DCC controled, b
