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DC wiring question on a new layout

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DC wiring question on a new layout
Posted by Ablebakercharlie on Monday, June 7, 2021 5:24 PM

First, thanks everyone for the advice on laying track.  Things are moving along and I have about 80% of the track down and have wired one loop of the layout and ran some trains, old tycos and athearns from 50 years ago that my father had and some new Bachmanns and Walthers that I recently purchased.

I want to start wiring the layout into blocks and some questions arose that I would like to share with you all for advice please.

I'll try to get to the point as succinctly as possible but if you need more information to offer guidance just let me know what you need and I'll post right back.

I ordered the Atlas 215 selectors for the blocks but I am now noticing that there is a connection for each switch for only one wire.  Does that insinuate that I would wire the layout with common rail and each block would get the second wire  from the selector?  If that is so, what I can't visualize is how to dispurse the wire for the common rail from the powerpack to all the different blocks?  I assume there is a device that takes one input from the power pack and then on the output side there are multiple termimals to send wires to the different blocks?  Please forgive me if there are terminology gaffs. I feel like a 3rd grader trying to ask a question.

On another note I would welcome thoughts on gauge of wire to use.  I scoured the forums looking for guidance and it seems for a DC  layout 18 to 20 gauge is sufficient.  I have Larry Pucketts's book on wiring and he suggests 12 to 14 gauge for DC but that seems like overkill. Or maybe not?  My layout is about 18 feet long and about 4 feet wide on the ends and narrow in the middle - dog bone shaped.

Thanks!  I would be happy to post my layout as grist for the mill if you are interested.

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Posted by jjdamnit on Monday, June 7, 2021 6:52 PM

Hello All,

Thank you for the update on your progress.

Since you are using Atlas controllers I suggest purchasing The Complete Atlas Wiring Book.

This is a valuable addition to any model railroaders library- -whether using DC or DCC.

It not only describes the application of the Atlas components but also gives schematics for the more technically inclined.

Unfortunately, it is currently listed as Backorder on the Atlas website.

To answer your question about the Atlas block switches- -yes, they do use a common ground that is NOT gapped on the "negative" rail for DC use.

A single wire from the "negative" side(s) of the cab(s) can be daisy-chained from one cab to the next then to the track or distribution unit.

If you are concerned about voltage drop on the "negative" common rail you have a couple of options:

  • You can use a single bus wire for the "negative" common and attach feeders to the track at set intervals, similar to a DCC bus but only for the "negative" side of the cab(s).

  • Another option would be to use terminal strips (A.K.A. terminal blocks or barrier strips). These come in "sizes" from 2- to 10-terminals.
  • To energize the entire strip you can fabricate jumpers from spade connectors and short pieces of wire or buy jumpers made of solid metal to connect the terminals.

  • From there it's a matter of running wires from the lugs (screw terminals) on the terminal strip to the track section. 

Before converting my 4' X 8' pike to DCC I had 16 control blocks (4 atlas controllers) with only a single "negative" common.

Because of the size of my pike I found 20 AWG wire sufficient for the power feeds for both the common and blocks.

For the turnouts I used a separate power source connected to two Capacitive Discharge Units through Atlas switch control boxes (#56). But that's another post.

Keep the questions coming, update us on your progress, and...

Hope this helps.

"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"

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Posted by RR_Mel on Monday, June 7, 2021 7:20 PM

My layout is 14’ x 10’ and the mainline is a twice around.  I have 14 blocks on the mainline.  I do not use common rail.  Each block is a homerun to my control panel using #19 solid bell wire.  Each block is controlled with a DPDT center off toggle switch.  My longest block run is about 16 feet.  #19 solid wire has 1.8 amp capacity, that's 1.8 amps to each block.  Two locomotives draw less than 1.8 amps working together.



I designed and built it before DCC.  In 2006 I went with DCC but I added a relay to switch the track power from my DC power pack to my new DCC controller.  I operate my layout dual mode, DC or DCC.





I use EURO Terminal Strips for my block wiring and Busbars for power distribution.








 

Mel
 
Modeling the early to mid 1950s SP in HO scale since 1951



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Posted by Lastspikemike on Monday, June 7, 2021 7:33 PM

I've just built such a layout.

Atlas uses common rail (it doesn't matter which "pole" is used as a common rail just btw) but there's no magic to that.

The only way common rail is different to standard DC or DCC two wire bus wiring is common rail relies on the rail only to feed current to one side of the circuit. Like a train set oval. 

That's the drawback. Any fair sized layout benefits from using multiple feeders to each rail for reliability. 

I recommend you ignore the common rail aspect (although all DC layouts are essentially common rail no matter what people say about how theirs isn't) and wire all your blocks with double isolators, each block will be a separate "layout" electrically. That way if you ever decide to convert to DCC or get a dual mode power supply like MRC Tech 6 you're all set. Troubleshooting a  divided into separate blocks with power fed to each rail is much easier than with true common rail where a failure of the common rail side can crash your whole layout and you have no idea where to start troubleshooting. For DCC not using common rail is a good idea for the same reason. In its simplest form DCC uses common rail for each rail. That's one big advantage of DCC, until it crashes.

To achieve this you run a power wire from one powerpack terminal under all of the  tracks. I run the red wire as the "common wire". This duplicates the common rail side of Atlas wiring diagrams so you can use all their switch gear easily. Then you drop rail feeders for the "common rail" to power one rail in each block.

The other "rail"  in each block is fed from the Black wire attached to the other pole of your powerpack but that wire runs through your 215 selectors. But this "bus" wire only runs to the input side of your 215 Selector switch(es). Then you run separate black wires from each 215 Output terminal to the desired blocks. The main wire from your powerpack to the input side of the 215 should be 16 gauge or heavier in preparation for maybe converting to DCC. 

The individual block wires can be smaller gauge if you wish because only one train  will draw power from each block at a time. However, unless funds are limited I'd run 16 gauge black wire also from your 215 to each block. 

The key to understanding common rail as opposed to common bus wire is you can connect more than one DC powerpack to the common rail. When converting to DCC you wil find you want to connect multiple power packs (DCC boosters) separalty not connected to a common terminal. Wiring each rail in each block to one polarity and isolating both rails within your blocks facilitates conversion to DCC.

This two wire to each block also makes wiring reversing sections easier to understand. In theory, every block can be wired for separate polarity control. Only reversing sectiins need this feature but it can help to realize that each block is electrically isolated.

Reversing sections cannot be controlled with a 215 selector. You need the Atlas Twin switch 210 (or make your own) or the Atlas 220 Controller which combines two Cab control (DC "Cabs" are power packs which is why Atlas uses common rail) with a separate reversing section control. 

Wiring more than one 220 in parallel is interesting and the Atlas diagrams are not correct. 

If on/off power is your only requirement for a "Block" or for sections within a Block you can use the Atlas Connector 205 which provides an on/off switch for one rail rather than a Cab selection which the 215 is for. The 215 also has an off position with the green button at center off (the red switches on the Twin and Controller are also center off as is the grey polarity switch on the Controller and the green Cab selector on the Controller.) 

Finally, I've encounters quality control issued with Atlas 220 Controllers made in a China so if you wire up with Atlas components and it doesn't work suspect the Atlas component first and test it with a multi meter to ensure the switches are actually working correctly.  

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Posted by Lastspikemike on Monday, June 7, 2021 7:44 PM

Or you could just build it like Mel's but then Atlas switch gear won't work for you. 

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Posted by FRRYKid on Tuesday, June 8, 2021 2:39 AM

I have a DC layout as well. (Don't intend to go DCC. Too many engines = too much expense.) I have 24 power blocks on it. (Reverse G shape 24' x 12' approx Rail yard area) As already stated if you're only using one power pack Atlas Connectors (yellow switch) are good enough (8 of them on my layout). Another thing that I have done on my layout is with my remote turnouts. On my Atlas twin coils each turnout has its own set of outer wires (Yellow and blue for me) but the green (control) is daisy chained from the control panel to each of them. (Less wire use and works just fine.) But how you do it is completely up to you. It is your layout.

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Posted by Water Level Route on Tuesday, June 8, 2021 5:33 AM

Like any wiring or control system, common rail has it's advantages and disadvantages.  It's been around for decades, so if that isn't indication that it works fine I don't know what is.  On a layout your size, it would be a good idea to fully insulate sections of it that can easily be disconnected from the remainder of the system should the need ever arise, but otherwise, carry on with your plan of using the Atlas selectors.  They will work fine for you.

Lastspikemike
Wiring more than one 220 in parallel is interesting and the Atlas diagrams are not correct.

I ran a layout for years using two Atlas 220's hooked up exactly as their diagrams indicate and it worked flawlessly.  Curious what you've run into.

Mike

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Posted by Lastspikemike on Tuesday, June 8, 2021 7:54 AM

Water Level Route

Like any wiring or control system, common rail has it's advantages and disadvantages.  It's been around for decades, so if that isn't indication that it works fine I don't know what is.  On a layout your size, it would be a good idea to fully insulate sections of it that can easily be disconnected from the remainder of the system should the need ever arise, but otherwise, carry on with your plan of using the Atlas selectors.  They will work fine for you.

 

 
Lastspikemike
Wiring more than one 220 in parallel is interesting and the Atlas diagrams are not correct.

 

I ran a layout for years using two Atlas 220's hooked up exactly as their diagrams indicate and it worked flawlessly.  Curious what you've run into.

 

 

I found that the positive and negative input connectors are not as illustrated. The "inner" terminals are the same polarity and the outer terminals are the same polarity. Atlas implies the opposite in their diagrams. The polarity also doesn't run "straight through" as you might expect. Older 220 with four outputs as well as four inputs reveal this oddity. Later design do not carry the "ground" polarity across the unit, Atlas no doubt realized that wiring the ground to the last 220 in a chain was all that was required actually so deleted the ground connectors, which were the outer pair of terminals at the input and the inner pair at the output. 

Looking at the schematic wiring diagram for the 220 confirms what I discovered myself by trial and error, after a frustrating afternoon of my layout not working. I also discovered the faulty brand new 220 units in similar fashion, tracking the internal wiring faults using a multi meter and the schematic if what was supposed to be connected and disconnected by the various sliders. Clever design, poor manufacture. 

A major deficiency of all Atlas switch units is the center off slider switches. The red polarity reversing switches in particular are very poor quality. The blue turnout motor switches are a close second.

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Posted by doctorwayne on Tuesday, June 8, 2021 10:48 AM

Lastspikemike
...The only way common rail is different to standard DC or DCC two wire bus wiring is common rail relies on the rail only to feed current to one side of the circuit. Like a train set oval. That's the drawback. Any fair sized layout benefits from using multiple feeders to each rail for reliability....

That may be so for block control to run more than one train at a time. 

My common rail DC layout, not counting staging yards, industrial sidings and areas of double track, has roughly 300' of mainline, all of it powered through these two wires...

Power is from an MRC Controlmaster 20, running through a Stapleton PWM walkaround throttle. I've run over a dozen locos at a time, without issues or slowdowns.  I use double throw/centre-off toggle switches to control the double-tracked areas and simple on/off toggles to control the individual tracks in staging yards and some industrial tracks.  Couldn't be simpler.

Several hard-to-reach turnouts are are powered by wall warts (1 Tortoise, 4 Rapido motor drives, and 2 PFM/Fulgurex rack drives.

Wayne

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Posted by Water Level Route on Tuesday, June 8, 2021 12:00 PM

Lastspikemike
I found that the positive and negative input connectors are not as illustrated. The "inner" terminals are the same polarity and the outer terminals are the same polarity. Atlas implies the opposite in their diagrams. The polarity also doesn't run "straight through" as you might expect. Older 220 with four outputs as well as four inputs reveal this oddity. Later design do not carry the "ground" polarity across the unit, Atlas no doubt realized that wiring the ground to the last 220 in a chain was all that was required actually so deleted the ground connectors, which were the outer pair of terminals at the input and the inner pair at the output.  Looking at the schematic wiring diagram for the 220 confirms what I discovered myself by trial and error, after a frustrating afternoon of my layout not working. I also discovered the faulty brand new 220 units in similar fashion, tracking the internal wiring faults using a multi meter and the schematic if what was supposed to be connected and disconnected by the various sliders. Clever design, poor manufacture.  A major deficiency of all Atlas switch units is the center off slider switches. The red polarity reversing switches in particular are very poor quality. The blue turnout motor switches are a close second.

Maybe I would have to see it, but I'm not following the issues you are bringing up.  Did you wire them from right to left?  Maybe using the "wrong" directional switches?  Seems odd that something that was manufactured right would all of a sudden be manufactured wrong and keep being manufactured wrong.  Not saying you didn't experience issues, but maybe there is something at play that was missed.

As for quality, I know people dog on Atlas's #56 switch controllers, but I've not had a failure with them personally, even using numerous ones for years, so I won't say they are poor quality.  I've also used numerous 220 controllers, 215 selectors, 210 twins, and 205 connectors for years with zero failures.  My only "complaint" is that the center point could have a little more resistance to help prevent moving past it.  Maybe you've got a shady supplier that's selling you Atlas knock-offs? Laugh 

Mike

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Posted by RR_Mel on Tuesday, June 8, 2021 1:13 PM

Common rail works fine and it has worked fine since the beginning of model railroading.  Personally I’ve always liked the ability to reverse direction in individual blocks and that requires both rails switched in a DC operation.

All my layouts from 1951 to 2006 were DC only and I’ve always switched both rails.  I also like the ability to just turn off the power to both rails to individual blocks.

When I went DCC in 2006 I tried the DCC Guru way (buss wiring) and didn’t like it.  The buss wiring screwed up my very nice signaling system so I went back to DC Block wiring for my DCC system.  Every thing works great, DCC isn’t rocket science and the data rate at 8.5kb will work fine on even the worst wiring out there.  All you need is the current carrying capacity to handle your load.  An HO locomotive uses about 600ma to 700ma under full load, figure out how many locomotives you will operate in a single block and size your wire for that amount of current.  In my case I never run more than two powered locomotives per train so I sized my wiring for a 2 amp max load per block.  I went with #19AWG solid bell wire from my local Big Box store, twisted red and white low cost wire.  I haven’t had any problems with my wiring for over 33 years.

I operate my layout dual mode, DC or DCC, never both at the same time.  To simplify the switching from DC to DCC and back I use a DPDT relay to switch the rail power between the two power supplies.  I use the Accessory voltage from my DC power supply to operate the relay coil so that when I turn on the DC power supply the relay pulls in and switches the rail power from the DCC controller to the DC power supply, fail safe and no memory cells needed.  I’m almost 84 and my memory cells aren’t what they used to be.

Mel
 
Modeling the early to mid 1950s SP in HO scale since 1951



My Model Railroad    
http://melvineperry.blogspot.com/
 
Bakersfield, California
 
Aging is not for wimps.

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Posted by Lastspikemike on Tuesday, June 8, 2021 2:10 PM

Water Level Route

 

 
Lastspikemike
I found that the positive and negative input connectors are not as illustrated. The "inner" terminals are the same polarity and the outer terminals are the same polarity. Atlas implies the opposite in their diagrams. The polarity also doesn't run "straight through" as you might expect. Older 220 with four outputs as well as four inputs reveal this oddity. Later design do not carry the "ground" polarity across the unit, Atlas no doubt realized that wiring the ground to the last 220 in a chain was all that was required actually so deleted the ground connectors, which were the outer pair of terminals at the input and the inner pair at the output.  Looking at the schematic wiring diagram for the 220 confirms what I discovered myself by trial and error, after a frustrating afternoon of my layout not working. I also discovered the faulty brand new 220 units in similar fashion, tracking the internal wiring faults using a multi meter and the schematic if what was supposed to be connected and disconnected by the various sliders. Clever design, poor manufacture.  A major deficiency of all Atlas switch units is the center off slider switches. The red polarity reversing switches in particular are very poor quality. The blue turnout motor switches are a close second.

 

Maybe I would have to see it, but I'm not following the issues you are bringing up.  Did you wire them from right to left?  Maybe using the "wrong" directional switches?  Seems odd that something that was manufactured right would all of a sudden be manufactured wrong and keep being manufactured wrong.  Not saying you didn't experience issues, but maybe there is something at play that was missed.

 

As for quality, I know people dog on Atlas's #56 switch controllers, but I've not had a failure with them personally, even using numerous ones for years, so I won't say they are poor quality.  I've also used numerous 220 controllers, 215 selectors, 210 twins, and 205 connectors for years with zero failures.  My only "complaint" is that the center point could have a little more resistance to help prevent moving past it.  Maybe you've got a shady supplier that's selling you Atlas knock-offs? Laugh 

 

Atlas wiring book page 37 figures 5-6 and 5-7 show incorrect connections from powerpacks to the 220. The 220 packaging diagram is also incorrect.

The actual connections for Cab B should be reversed. Fig 2-9  on page 16 shows why. The input terminals that provide the flow through current to the output terminals clearly show the one pole passing through the uppermost terminal in the diagram and the lowermost terminal is the same polarity. In fact, the newer 220 does not pass the current through to  the inner output terminals at all. Those terminals no longer exist. I'm not sure what they ever did since Atlas gives explicit instructions about the order of ganging new 220 to older types. 

You can also see from the schematic of the Cab switch portion that the input terminals are reversed for Cab A relative to Cab B. 

The schematic fails to show how the one common rail polarity is carried through ganged 220's, indeed, the common terminal connection for even the single 220 is not drawn on the schematic. The red reversing switches must be in the center off position for each 220 in a gang except the last one. I suspect what is not shown in the schematic is the power flow through the "off" reversing switches to the C or common terminal in the last 220 in the gang.

My "shady" supplier refunded my money on the defective 220's I bought. I showed him the fault using that schematic and my multi meter. 

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Posted by riogrande5761 on Wednesday, June 9, 2021 10:52 AM

Ablebakercharlie
On another note I would welcome thoughts on gauge of wire to use.  I scoured the forums looking for guidance and it seems for a DC  layout 18 to 20 gauge is sufficient.  I have Larry Pucketts's book on wiring and he suggests 12 to 14 gauge for DC but that seems like overkill. Or maybe not?

I wouldn't think it should matter DC or DCC.  Power attenuates over longer distance.  So it depends on how long your bus is.  There are tables you can google for DCC, for example, that would be also good for DC.

Tables I've looked at indicate that runs of less than 50' you can use 14 AWG wire for your bus.  Longer than that and 12 AWG.  I purchase rolls of 14 AWG house wire from Lowes for my bus and am sticking with that for size and bus length.

I am am running staging track feeders at around 8 feet so using 20 AGW bell wire for those from Lowes.

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Posted by Texas Zephyr on Thursday, June 10, 2021 8:42 PM

Ablebakercharlie
On another note I would welcome thoughts on gauge of wire to use.  I scoured the forums looking for guidance and it seems for a DC  layout 18 to 20 gauge is sufficient.  I have Larry Pucketts's book on wiring and he suggests 12 to 14 gauge for DC but that seems like overkill.

I think so too.   I use 18 gauge sprinkler system wire.

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Posted by CSX Robert on Friday, June 11, 2021 8:26 AM

Lastspikemike
...The only way common rail is different to standard DC or DCC two wire bus wiring is common rail relies on the rail only to feed current to one side of the circuit...

No, the way common rail is different is one rail is electrically common throughout the layout (except for reversing sections if the layout has any).  Most larger common rail layouts use multiple feeders for the common rail instead of relying on just the rail for feeding current to the common side of the circuit - they are still "common rail" layouts because they still use an electrically common rail.

Lastspikemike
...although all DC layouts are essentially common rail no matter what people say about how theirs isn't...

I don't know how you came about this idea but it's simply not true.

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Posted by CSX Robert on Friday, June 11, 2021 8:38 AM

riogrande5761
...I wouldn't think it should matter DC or DCC.  Power attenuates over longer distance.  So it depends on how long your bus is.  There are tables you can google for DCC, for example, that would be also good for DC...

You're half right, if it will work for DCC it will work for DC, but the opposite is not necessarily true.  Heavier gauge wiring is recommended for DCC for multiple reasons - the main ones being heavier loads (multiple trains running from single power supply) and detecting short circuits.

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Posted by Lastspikemike on Friday, June 11, 2021 8:38 AM

CSX Robert

 

 
Lastspikemike
...The only way common rail is different to standard DC or DCC two wire bus wiring is common rail relies on the rail only to feed current to one side of the circuit...

 

No, the way common rail is different is one rail is electrically common throughout the layout (except for reversing sections if the layout has any).  Most larger common rail layouts use multiple feeders for the common rail instead of relying on just the rail for feeding current to the common side of the circuit - they are still "common rail" layouts because they still use an electrically common rail.

 

 
Lastspikemike
...although all DC layouts are essentially common rail no matter what people say about how theirs isn't...

 

I don't know how you came about this idea but it's simply not true.

 

 

I look at the wiring and the tracks. It's correct. Your perspective may disguise the reality. Layout wiring is pretty simple stuff. Red wire to one rail, black wire to the other rail. 

In fact, one huge advantage of DCC is you can just hook up two wires to one connection track and your whole layout will be powered for multiple locomotive operation. Two common rails. No bus wires at all.

Adding bus wires and feeders doesn't make it not common rail wiring. Cutting power to only one rail is what makes a system "common rail" straight toy speaking. For DCC you don't need a "control rail", Bith rails are common rails.

It's the addition of double isolating blocks that does break up the common rail(s)  wiring system. You need to do that only if you add power boosters in DCC or want full electrical control of your DC blocks. 

Don't mention reversing sections. They don't work with common rail at all. DCC or DC. (Oops, you did already) 

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Posted by CSX Robert on Friday, June 11, 2021 9:04 AM

Lastspikemike
I look at the wiring and the tracks. It's correct. Your perspective may disguise the reality. Layout wiring is pretty simple stuff. Red wire to one rail, black wire to the other rail.  In fact, one huge advantage of DCC is you can just hook up two wires to one connection track and your whole layout will be powered for multiple locomotive operation. Two common rails. No bus wires at all. Don't mention reversing sections. They don't work with common rail at all. DCC or DC.

I think maybe you're confused about what common rail wiring is.  Take a DC layout with two blocks (to really be useful you need more than two bloacks, but this is just for demonstration), two cabs, and two trains running - block 1 switched to cab 1 and block 2 switched to cab 2.  With normal (not common rail) wiring, you have cab 1 output A wired to block 1 rail A, cab 1 output B wired to block 1 rail B,  cab 2 output A wired to block 2 rail A, cab 2 output B wired to block 2 rail B.  Within each block you may have one feeder wire per rail or you may have a dozen, it doesn't matter.  You have two isolated circuits - there is nothinig common between them - there is no way this could be described as a common rail layout.

 

Now, if you wire cab 1 output A and cab 2 output A together and remove all of the isolating gaps between the blocks in rail A, but leave them in rail B, you have a common rail layout.  It doesn't matter if you have one feeder or 100 for the common rail, it's still common rail because that entire rail is common and tied back to the common outputs from the two (or more) power packs.

 

Lastspikemike
Don't mention reversing sections. They don't work with common rail at all. DCC or DC.

Common rail doesn't work with reversing sections, but you can certainly have reversing sections on a common rail layout, you just have to have the reversing section completely isolated.  It's still considered a common rail layout because the rest of the layout is common rail.

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Posted by Lastspikemike on Friday, June 11, 2021 9:09 AM

I'm not confused. The idea of common rail confuses people because it seems to involve some of the things you describe. It doesn't.

A toy train uses common rail power. A DC or DCC system with control rail gaps is common rail. Add just one reversing section and you no longer have a common rail system.

Too many people don't understand common rail because of the way it is described. It's just toy train wiring. 

Things get a bit more complicated when you add a second power pack to a DC system in that you have to make sure you connect the red wires and the black wires correctly to the second powerpack (duh). You really don't want to do that if you add a second power booster to a DCC layout. In fact, there are good reasons not to use full common rail wiring when building a DC layout but electrically your DC layout will still be common rail even if double isolated unless you also control your blocks with DPDT instead of SPDT which you forgot to mention. 

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Posted by CSX Robert on Friday, June 11, 2021 9:15 AM

Lastspikemike
Adding bus wires and feeders doesn't make it not common rail wiring. Cutting power to only one rail is what makes a system "common rail" straight toy speaking. For DCC you don't need a "control rail", Bith rails are common rails. It's the addition of double isolating blocks that does break up the common rail(s)  wiring system...

It looks like you added this while I was replying.  If you understand that double isolating the blocks breaks up the common rail wiring, then how do you come to the conclusion that " all DC layouts are essentially common rail."

Lastspikemike
You need to do that only if you add power boosters in DCC or want full electrical control of your DC blocks. 

Again not true, with common rail wiring you have full electrical conrol of the DC blocks.

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Posted by Lastspikemike on Friday, June 11, 2021 9:20 AM

CSX Robert

 

 
Lastspikemike
Adding bus wires and feeders doesn't make it not common rail wiring. Cutting power to only one rail is what makes a system "common rail" straight toy speaking. For DCC you don't need a "control rail", Bith rails are common rails. It's the addition of double isolating blocks that does break up the common rail(s)  wiring system...

 

It looks like you added this while I was replying.  If you understand that double isolating the blocks breaks up the common rail wiring, then how do you come to the conclusion that " all DC layouts are essentially common rail."

 

 
Lastspikemike
You need to do that only if you add power boosters in DCC or want full electrical control of your DC blocks. 

 

Again not true, with common rail wiring you have full electrical conrol of the DC blocks.

 

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 switching for reversing sections). I know. I wired one. All the red rails on my double isolated DC layout are connected together by bus bars under the layout. Why? So I can easily connect a DCC power booster to the entire layout but still retain the option of running block control DC. I can add polarity reversing capability to any block by disconnecting the red wire at the appropriate bus bar and connecting it to a DPDT instead.

Much of the confusion about reversing loops is caused by incomplete understanding of common rail wiring.

Alyth Yard

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Posted by CSX Robert on Friday, June 11, 2021 9:32 AM

Lastspikemike
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 switching for reversing sections). I know. I wired one. All the red rails on my double isolated DC layout are connected together by bus bars under the layout.

If the rails are tied together under the layout, then they are not isolated, if they are isolated, then it is not common rail.

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Posted by gregc on Friday, June 11, 2021 10:12 AM

Lastspikemike
Things get a bit more complicated when you add a second power pack to a DC system in that you have to make sure you connect the red wires and the black wires correctly to the second powerpack.

doesn't matter.   cab power needs to be reversible

Lastspikemike
Much of the confusion about reversing loops is caused by incomplete understanding of common rail wiring.

and unnecessary described constraints (see above)

 

power can be switched between cabs using an SPDT for common rail blocks and using DPDT for switching between cabs in reversing sections.

regardless of common rail or not, there is a potential for a short at the sum of both cab voltages.

and of course, things need to be wired properly.

greg - Philadelphia & Reading / Reading

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Posted by CSX Robert on Friday, June 11, 2021 10:13 AM

Lastspikemike
Things get a bit more complicated when you add a second power pack to a DC system in that you have to make sure you connect the red wires and the black wires correctly to the second powerpack (duh).

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.

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Posted by richhotrain on Friday, June 11, 2021 10:24 AM

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?

Rich

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Posted by gregc on Friday, June 11, 2021 10:25 AM

CSX Robert
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 don't believe there are any restrictions in having multiple blocks within a reversing section allowing trains being operated by separate cabs.   

the power for those blocks would go thru the reversing section reversing switch.

not sure if this is what you mean that the reversing sections are (or can be) common rail

greg - Philadelphia & Reading / Reading

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Posted by gregc on Friday, June 11, 2021 10:27 AM

richhotrain
Is there any way to sort this all out in order to salvage this thread?

what do you find confusing?

greg - Philadelphia & Reading / Reading

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Posted by richhotrain on Friday, June 11, 2021 10:30 AM

A lot of the replies seem contradictory to one another. As I said, somebody must be right and somebody must be wrong.

Rich

Alton Junction

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Posted by CSX Robert on Friday, June 11, 2021 10:38 AM

gregc
not sure if this is what you mean that the reversing sections are (or can be) common rail

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.

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Posted by gregc on Friday, June 11, 2021 1:31 PM

CSX Robert
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

right, and of course.   thanks

richhotrain
A lot of the replies seem contradictory to one another.

can you site a specific example.  i only see confusing lengthy replies that may be self-contradictory

Atlas has proven that common-rail works.

greg - Philadelphia & Reading / Reading

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