# Common rail – the good and the bad?



## steam5 (Jun 22, 2008)

How have you wired your railroad for DCC, have you used a common rail between blocks / districts? Why or why not?

I think I’ve read that in general one should not use common rail wiring???

In HO I think I will be forced to use common rail because brass steamers pick-up one rail on the loco and the other on the tender, is this true?

When I wire my G layout should I avoid common rail between districts?

Any thoughts and experience would be a great help.

Alan


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## DKRickman (Mar 25, 2008)

Common rail wiring is not reccomended for DCC, because there is a possibility that one booster can feed back into another (via internal circuitry), especially if they are installed with opposite polarities. At least, that is my understanding - I'm sure there are others here who can give a lot more information. 

On DC and in HO, common rail is fine, but never required. Your brass engines will run exactly the same regardless of whether you use common rail or not. It's a great way to simplify wiring, and works without a hitch (unless for some reason you have a bunch of throttles which are all fed from the same transformer). 

When I wire my (HO) layout, it will be broken into two power districts, with insulated gaps in both rails. These will initially be wired together underneath, but I will have the option to split them in the future, if traffic increases.


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## Bill Swindell (Jan 2, 2008)

The key to using common rail is that with it, you MUST not have any common wiring in your power supplies. I'm not sure about DCC but with analog throttles, if you run common rail, the throttles must run from separate transformers. Our HO club runs separate transformer windings for each throttle and we gap both rails too. This was just a case of double protection. By the way, we stagger our rail gaps also. I suggest that you do not run common rail. That way, you will not have to worry about it. The steam engine pickup is not an issue.


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## Greg Elmassian (Jan 3, 2008)

The only reason common rail is even "Tolerated", meaning it is explained how to deal with it, by the DCC manufacturers, is because old HO layouts often had common rail. 

Don't do it, it's not worth the potential hassles. In addition, debugging bad conductivity on the rails is more difficult. 

Regards, Greg


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## TonyWalsham (Jan 2, 2008)

Bear in mind gentlemen that "common rail" is the method of wiring LGB used all those years.


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## Greg Elmassian (Jan 3, 2008)

Uhh... probably not for DCC.... for DC yes... you can't use autoreversers with common rail easily. 

Regards, Greg


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## toddalin (Jan 4, 2008)

Posted By Greg Elmassian on 19 Jul 2009 05:06 PM 
Uhh... probably not for DCC.... for DC yes... you can't use autoreversers with common rail easily. 

Regards, Greg Sure you can and I do.

Put the reverser between the power supply and the control panel/track and all of the track sections (blocks) on that power pack will reverse. Now if you have diode protection on your sidings, you can set your turnouts to direct your trains between any two sidings where they will go back and forth between the sidings.

We even do this out between the mainline and lake siding.


I don't know about the intricicies of dcc, but the common rail saves lots of wiring. I use two 24-pin cables (48 actual wires) between my control panel and track/turnouts. 21 of these wires power turnouts, 22 power blocks, 2 power a "tail block," one turns on my automation circuits, and 2 are used for the common rail that must carry all three 16.5 amp power packs, 16.5 amp power pack for the 21 turnouts and automation, and 16.5 amps for the building and effects lighting. If I didn't use a common rail, I would have to run an additional 44 wires and there is no way I could squeeze it all in the various boxes.


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## Greg Elmassian (Jan 3, 2008)

Umm... Todd.... you are using diode protection on your sidings on *DCC*? Huh? 

Notice the 4th word in my post... *DCC*..... 

The thread is about *DCC*... you are talking *DC*.... ..... 

Back to the topic.... common rail bad idea on *DCC*, for the reasons I gave... notice I did not say impossible, just not easy and not a good idea.

(by the way, you have an autoreverser on *DC*? an _auto_reverser is very common on a DCC layout, but not on DC, and common rail makes them very difficult

Come on guys, let's read the thread and what it is about, rather than just keying in on a phrase like "common rail"

This is the DCC forum and the question was about common rail and DCC.


Regards, Greg


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## toddalin (Jan 4, 2008)

Posted By Greg Elmassian on 19 Jul 2009 06:23 PM 
Umm... Todd.... you are using diode protection on your sidings on *DCC*? Huh? 


(by the way, you have an autoreverser on *DC*? huh? who makes it?) (autoreverser is not a "reverser" whatever that is)

Come on guys, let's read the thread and what it is about, rather than just keying in on a phrase like "common rail"

This is the DCC forum and the question was about common rail and DCC.


Regards, Greg I was just addressing your comment, so who was off-topic?

"for DC yes... you can't use autoreversers with common rail easily."

Yes I have reversers on DC and I make them


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## steam5 (Jun 22, 2008)

Thanks for the answers. I’m 100% sure I’ll be wiring the garden railway with out a common rail, which was my plan. 

If I use the similar scheme for my HO layout will my brass steamers stall over the joint? Remember the loco picks up one rail and the tender the other?


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## Greg Elmassian (Jan 3, 2008)

Uhhh.. you thought I was referring to DC with the term "autoreverser"? OK... I understand the literal sense of your reply. 

I am unaware that the term "autoreverser" is ever applied to anything other than DCC. The intent of my answer to "common rail on DCC" was: 

*No, not on DCC, yes people use it on straight DC.... No, DCC autoreversers are not easy to use with common rail. *

Sorry, I will be much more explicit in the future. 

The question is clearly about DCC and common rail... whatever transgressions in clarity I have performed I apologize... but really: 

"I don't know about the intricicies of dcc, but the common rail saves lots of wiring." is clearly NOT about DCC.... since you are basically admitting you don't know about DCC and common rail. 

That's what got me to respond.... why confuse the issue talking about DC? It's a different can of worms, and that was what I was striving to put forward. 

Anyway, that's why I posted back, it seemed you were more interested talking about DC and common rail, which is very different than DCC and common rail. (and the use of DCC autoreversers is one good reason why)

Regards, Greg


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## StanleyAmes (Jan 3, 2008)

Perhaps I can provide a different opinion as the common rail topic is one of the great myths surrounding DCC.

Basically the responses of the years tend to follow the party line of the manufacturers system of the person responding.

Common rail is an excellent method for wiring ones railroad, saves a lot of wire and is very effective. Unfortunately it is more demanding in how a layout is wired then 2 rail wiring, and because of that I normally recommend avoiding it for new layouts.

Basically one common point is a good thing and most all DCC systems have a common provision somewhere. The problem is that multiple commons can be a bad thing with strange things as a result, especialy in some detectors and signal systems.

Some DCC power stations do not support common rail and others have a built in common that must be removed first. For these types of power stations it is best to not use them on common rail layouts. Other power stations (boosters) are totally isolated and if a common is desired it must be installed. These unts work equally well with common rail and 2 rail wireing.

Hope that helps

Stan Ames
http://www.tttrains.com/largescale/


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## Greg Elmassian (Jan 3, 2008)

Yep, to be avoided... 

Also, in a DCC layout you have a lot less track wiring, unless you are doing "block detection" you have many fewer feeders, I only run feeders every 30 to 40 feet, and that is overkill for most people. 

The cost of wire is very little, and I use 10 gauge... 

The problems of getting ground loops, and running afoul of autoreversers, and tracking down bad/poor connections and the boosters that do not support common rail make it a bad idea in general for most people. 

I do not see that you provided a different opinion. 

Regards, Greg


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## Dan Pierce (Jan 2, 2008)

If you have 2 separate power supplies and tie the low side of one to a common rail and the high side of the other to the common rail, you have a voltage over 48 volts between the uncommon rails and this is dangerous. 
This is for DCC or DC and even AC power sources!! 

For the smaller scales, this voltage is much less as they do not use the high voltages we use for our garden railrroads. 

In the electronics industry, 30 volts is now the maximum voltage differential allowed for humans to contact. Anything higher than that requires saftey switches and plastic insulating covers to prevent contact. 
We are even not allowed to wear jewelry due to heat from shorting out power sources. 

I know electricity savvy people like Greg would not do this, but to the non electrical knowledgeable person, this can happen , therefore the common rail is not a good idea. 

Lay on the ground across your rails on a hot summer day while working in the RR and sweating and just feel the power of 24 volts running thru your body while running trains!!! 
Think what double that can do esp if a heart condition exists!!


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## toddalin (Jan 4, 2008)

Posted By Dan Pierce on 21 Jul 2009 05:08 AM 
If you have 2 separate power supplies and tie the low side of one to a common rail and the high side of the other to the common rail, you have a voltage over 48 volts between the uncommon rails and this is dangerous. 
This is for DCC or DC and even AC power sources!! 



Not nearly as dangerous as driving to work though traffic that lots of people do every day. Life is too short to worry about stuff like that.

I've never heard of anyone receiving a 48 volt shock from touching their rails, and the only way it could happen is if they were to touch two separate areas of "hot" rail under the control of the two power packs that were at opposite polarity, and I don't even know that this would do it.

However, I will say this. On my "leap frog" I use half wave 22 volts to trigger the two turnouts and latching relay. At one time I had an engine parked over a reed switch such that the magnet kept it all activated. When a train pulled up on the other track and triggered the turnouts to the opposite direction, there was a differential of ~44 volts and a few diodes fried on the circuit board.

I redid the leap frog so that when either reed activates and triggers its relay to throw the turnouts, a leg on that relay also disconnects and "locks out" the other reed switch to keep it from activating and causing a repeat of this problem.

BTW, the minimum reported voltage for electrocution is ~66 volts.


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## Greg Elmassian (Jan 3, 2008)

Wikipedia reports as low as 32 volts: http://en.wikipedia.org/wiki/Electric_shock 

When my arms are sweaty, touching my 23v RMS DCC rails is uncomfortable. 

I have found frogs electrocuted on my rails, rear legs on one rail, front ones on the other. 

Regards, Greg


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## toddalin (Jan 4, 2008)

Posted By Greg Elmassian on 21 Jul 2009 08:39 PM 
Wikipedia reports as low as 32 volts: http://en.wikipedia.org/wiki/Electric_shock 

When my arms are sweaty, touching my 23v RMS DCC rails is uncomfortable. 

I have found frogs electrocuted on my rails, rear legs on one rail, front ones on the other. 

Regards, Greg 

Can't believe evrything you read in Wikipedia. Besides, they don't provide a source for the statement.

When my arms are sweaty, I can certainly "feel" the voltage across my track (burns).

I've yet to find a fried lizard, though I have found one that was suffering from a brain hemorrage when a date from the tree hit him on the head. I guess that dates are more dangerous that track voltage. Heck, people die from getting hit by coconuts!


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## steam5 (Jun 22, 2008)

Posted By Greg Elmassian on 21 Jul 2009 08:39 PM 
Wikipedia reports as low as 32 volts: http://en.wikipedia.org/wiki/Electric_shock 

When my arms are sweaty, touching my 23v RMS DCC rails is uncomfortable. 

I have found frogs electrocuted on my rails, rear legs on one rail, front ones on the other. 

Regards, Greg 
Greg, your going to need a frog crossing on you railway!


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## Dan Pierce (Jan 2, 2008)

I have some live frogs on my track... wait, those are metal switch frogs!!!! 

OOps. one is an Aristo and now it is dead, must be that sorta water resistant micro switch again......... 


Just fr laffs.....


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## Greg Elmassian (Jan 3, 2008)

I agree, you cannot trust everything on wikipedia. 

I assume by your response you stand by your 66 volts. (which did not have a reference either).

Well, I hope the following document is not likewise untrusted, it is by a PHD from a university:

http://bme.ccny.cuny.edu/faculty/mb...Review.pdf

Table 2 shows various situations, where paralysis of the respiratory muscles can occur in as low as 20 volts, and most of the results were in the 25-30 volt range. The table shows results from eight different studies. I'd say that's good enough!


I think that if someone had their lungs paralyzed and died, I'd call it electrocution. You might argue you want fibrillation or complete standstill of the heart muscle, but I say if you are dead because of an electric current, you were electrocuted.


Point is, do not think voltages under 60 is safe if you are perspiring heavily or wet, and run it through your central core. 




Regards, Greg


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## DKRickman (Mar 25, 2008)

Posted By steam5 on 19 Jul 2009 06:53 PM 
Thanks for the answers. I’m 100% sure I’ll be wiring the garden railway with out a common rail, which was my plan. 

If I use the similar scheme for my HO layout will my brass steamers stall over the joint? Remember the loco picks up one rail and the tender the other? 


I guess folks got too busy "discussing" all sorts of things to actually answer this question.

Whether you use common rail or not makes no difference to your steamers, in any scale. Think about it this way - if two adjacent blocks are powered from the same source, and at the same polarity, then the rails are electrically connected (via block/cab switches, etc.) and the model will keep right on going. That's true for common rail wiring, as well as having both rails gapped. If your model bridges a gap to a block which is NOT at the same polarity and powered from the same source, it will either create a short (and hopefully shut down the power supply), stop, or start running on the new supply. This is also true no matter how the railroad is wired.

One thing to remember is that, for common rail wiring, you only need a single pole switch for a given block, whereas you need a double pole switch if both rails are gapped. You'll still need a DPDT for reversing the polarity of a block, but the previous statement will hold for block selector switches.


If you want my advice, I'd go ahead and gap both rails. Remember, you shouldn't be running your locomotives past the gaps anyway, unless they're supposed to be there, in which case the blocks should be controlled from the same throttle.


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## Greg Elmassian (Jan 3, 2008)

The thread is about common rail in DCC. 

If you have gaps / separate blocks in DCC it's only for 2 reasons: 

1. separate blocks for block detection. In this case, there is no polarity difference on either side of the gap. So nothing can go wrong. 
2. insulated sections for reversing loops or isolated sections for local short circuit detection. In this case you have either a circuit breaker or an autoreverser which will change the polarity if needed. 

In neither case do you need a DPDT switch for reversing the polarity, this is NOT track power DC, he is asking about DCC. 

I know everyone is trying to be helpful, but I think all these comments/suggestions that are only about DC serve only to further confuse someone who was already uncertain (because he asked the question).... 

This is the DCC forum. We do not use DPDT switches or anything else from the dark ages.









Regards, Greg


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## steam5 (Jun 22, 2008)

Posted By DKRickman on 27 Jul 2009 03:17 PM 

Think about it this way - if two adjacent blocks are powered from the same source, and at the same polarity, then the rails are electrically connected (via block/cab switches, etc.) and the model will keep right on going. 


Kenneth,

What about between powder districts which are power by different boosters (different sources), this is where I think I will have troubles with my brass steamers, any thoughts?

Alan


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## steam5 (Jun 22, 2008)

Greg, your right with the DC comments above. I have wired block controlled layouts with multiply cabs before and quite confident. I’m not confused, but if I had minimal experience I’d be in trouble. 

DCC and DC should be wired slightly different to get the full potential of each system. 

I’d still like to know any information about double breaks between boosters (with separate power supples) and what my brass steamers will do. If I had a second booster at home I’d just hook them up and try. 

I will be wiring a G layout up soon and I plan to use double breaks between power districts and common rail wiring within that district, I do not need to worry about locos with split pick ups.


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## Greg Elmassian (Jan 3, 2008)

Different boosters, if in phase should not have a problem with spanning the gaps. 

Most manufacturers would probably recommend that each power district has separate circuit breaker protection... the DCC specialties stuff would work fine for you. 

The autoreversers for reversing loop functions are great, just invisible in operation. 

Regards, Greg


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## steam5 (Jun 22, 2008)

Thanks Greg, 

I’ll give it a shot when I get closer, nothing wrong with a bit of experimenting. 

The breakers are important, nothing worse than having the booster shut down because someone ran a point or something similar on the other side of the railway. 

Alan


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## Greg Elmassian (Jan 3, 2008)

The nice thing is that you could set the current limitation to 5 amps in a block for example, rather than the whole 10 amps (using an NCE as an example). 

I like the DCC Specialties stuff becasue you can get a number of variations on the basic autoreverser and/or circuit breaker, and they can normally be programmed by jumper and/or CV's. 

Regards, Greg


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## StanleyAmes (Jan 3, 2008)

If you have a locomotive with offset pickups common in brass steamers in the smaller scales (pickup on one side on the locomotive and pickup on the tender on the other side) you must have a common somewhere or the locomotive will stall over the gap between boosters (power stations).

Some power stations have a built in common, some have an optional common that the user can install, or you can use common rail or common supply. The key is to have one common. Its really easy. Just follow the instructions that come with your booster.

Stan Ames

http://www.tttrains.com/largescale/


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## Greg Elmassian (Jan 3, 2008)

To my knowledge, there is no such animal in G scale. 

Has anyone found this type of arrangement? Only one side pickup on the loco, and only the other side on the tender? 

Regards, Greg


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## steam5 (Jun 22, 2008)

Thanks Stan for the clarification, My Lenz system does discuss common rail set ups, and I will follow it, or it could be an expensive mistake! I wanted to make sure the brass loco thing was or wasn’t a myth. 

Greg, I haven’t come across a slipt pick up in G (big tick to G scale manufactures!), that’s why I’m happy to wire the G layout up right now with a double break between districts to make some things like auto reversers easier to implement as you mentioned earlier.


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## Greg Elmassian (Jan 3, 2008)

Sounds good, safest approach. 

Thanks for reminding me Stan, different manufacturer's do handle the "common" differently. 

I do believe there is normally a simple way to allow the boosters to share a common such that 2 boosters will "cooperate" across the insulators with a "split pickup" loco... but I need to research it... 

Regards, Greg


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