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DC wiring question on a new layout

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Posted by ATLANTIC CENTRAL on Saturday, June 12, 2021 7:24 PM

I was able to see and download the track plan, I will get back to you as soon as I can look it over.

To the right of your screen, should be your account profile info. There should be a button that says "messages" - that is the private message portal.

If it's not there or does not work, don't be concerned, not all the features work correctly for everyone, the software is old.....

Be back to you soon,

Sheldon

    

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Posted by Lastspikemike on Saturday, June 12, 2021 8:10 PM

Looking at the 220 schematic again I see how Atlas indicates the center off flow through for the Common terminal. The lower Cab B reversing switch is shown in the center off position and the direct connection is shown. Cab A reversing switch is shown in the live position activating the Block output connections. You would never actually operate the 220 in this configuration.

The remainder of my remarks are correct. 

Alyth Yard

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Posted by CSX Robert on Saturday, June 12, 2021 9:09 PM

Lastspikemike

Looking at the 220 schematic again I see how Atlas indicates the center off flow through for the Common terminal. The lower Cab B reversing switch is shown in the center off position and the direct connection is shown. Cab A reversing switch is shown in the live position activating the Block output connections. You would never actually operate the 220 in this configuration.

Thge schematic you're looking at must not be the same as the one Greg posted then(which is also available on the Atlas website).  That schematic shows both cabs A and B in the center position, with the cab inputs connected directly to the right side outputs and no connection to common (because again, with mutiple 220's you can not pick up common until after the cab direction switches in the last 220).

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Posted by gregc on Sunday, June 13, 2021 5:10 AM

CSX Robert
 
Lastspikemike

Looking at the 220 schematic again I see how Atlas indicates the center off flow through for the Common terminal. The lower Cab B reversing switch is shown in the center off position and the direct connection is shown. Cab A reversing switch is shown in the live position activating the Block output connections. You would never actually operate the 220 in this configuration.

greg - Philadelphia & Reading / Reading

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Posted by SeeYou190 on Sunday, June 13, 2021 8:36 AM

Lastspikemike
So, clearly, there is not a commonly accepted definition of common rail.

I am pretty sure there has been a universally understood definition of common rail DC wiring for 60+ years.

Confused

-Kevin

Wink Happily modeling my STRATTON & GILLETTE RAILROAD. A Class A line located in a personal fantasy world of semi-plausible nonsense on Tuesday, August 3rd, 1954.

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Posted by Lastspikemike on Sunday, June 13, 2021 8:41 AM

Did we also verify that, assuming the two power packs depicted by Atlas are identical, that Atlas shows the positive and negative outputs connected incorrectly to the 220? If yiu connect as shown you will get a dead short. 

The last 220 in a gang is connected to the 215 Selector through the outer output terminals. The two inner output terminals are not connected to a 215 at all. In fact if you connect a newer 215 to an older 220 with terminal bars you have to cut off the two inner output terminals in order to get the 215 close enough to connect.  The original 220 did not have pass through Common output terminals.

The 220 reversing switches both pass through the Common connection and are center off, if you do not have the reversing switches on all but the last 220 in the center off position you will have open circuit. 

The actual reason to use a 220 is for its integral reversing switch.

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Posted by CSX Robert on Sunday, June 13, 2021 8:42 AM

gregc
the arrow is confusing in the controller schematic (upper right). there is a permanent connection between the screw terminals.   I verified this with a multimeter with the reversing switches centered.    they've confusingly drawn the connection going thru the switch.

The arrow is just showing one position of the reversing switch.  There is not a direct connection between the cab input and output terminals, the cab reversing switches are three position switches and the center position does connect the inputs straight to the outputs.  The other two positions connect one leg of the corresponding cab to the outer output terminal (top terminal for cab A and bottom terminal for cab B) and the other leg to the common terminal.

gregc
and yes, if the plastic cab reversing switch is in the middle, there is no connection between common rail terminal, C, power pack.   The switch should not set in that position

The switch is supposed to be set in that position on all but the right-most controller when there are two or more.

gregc
the bottom diagram also indicates that the common rail connection C is from the right-most 220 controller, meaning that it is the result of passing thru several cab reversing switches on one or more 220 controllers as well as the throttle itself.

The common does pass through all of the controllers (on the cab inputs/outputs), but you cannot pick it up until the last one because you cannot determine which leg of each cab is common until after the reversing switches in the last controller.

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Posted by Lastspikemike on Sunday, June 13, 2021 8:50 AM

SeeYou190

 

 
Lastspikemike
So, clearly, there is not a commonly accepted definition of common rail.

 

I am pretty sure there has been a universally understood definition of common rail DC wiring for 60+ years.

Confused

-Kevin

 

And what would that be?

I suggest evidently not.

I propose that Common Rail is more correctly described as "Control Rail" since that is its distinguishing feature. The idea is you can select and electrically control separate blocks with isolating gaps in only the one rail.  You do not need two powerpacks.

The misconception that you need more than one Cab to have a Common Rail layout probably arises from the advantages Common Rail affords if you add Cabs to a DC layout. 

For DCC you can use Common Rail with one powerpack and single control rail quite conveniently. What you don't want to do is try running Common Rail with multiple booster units. This is very important to get straight in your mind. 

Common Rail is ideal for DCC, in its simplest form, with one booster usually integral with the command station. What could be easier to wire? You don't even need any blocks. Hence my remark about both rails being common rails in the simpler DCC layouts. 

Somewhat ironically, if you wish to run DC locomotives on occasion using say a Tech 6 then you'll want to put at least some control rail sections into your layout (to park the DCC locomotives) unless you want to have to take all your DCC locomotives off the layout just to run the one DC locomotive. Now that's a nuisance.

Some new trainsets now are coming out with the advantages of simple two rail wiring and the benefits of DCC, it's like magic.

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Posted by SeeYou190 on Sunday, June 13, 2021 8:58 AM

Lastspikemike
And what would that be?

I think you are purposely "playing dumb" to start some discord. There is no way you do not understand common rail.

Anyway... common rail has one continously electrically connected rail that shares one terminal in common with each power pack output. That "rail" is "common" to all power sources.

There, now you don't need to pretend that you don't understand.

Zzz

-Kevin

Wink Happily modeling my STRATTON & GILLETTE RAILROAD. A Class A line located in a personal fantasy world of semi-plausible nonsense on Tuesday, August 3rd, 1954.

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 9:32 AM

Robert gets it.

The Atlas Controller serves three functions. It provides a MAIN LINE reversing switch for each throttle AFTER a power tap for a reversing loop. It provides a cab selection switch for the reversing loop, and it provides the necessary separate reversing switch for that loop.

IF you have more than one reverse loop, Controllers are added to the left for each additional loop.

The cab reverse switches on the ADDITIONAL Controllers must remain in the center pass thru position on those controllers. Only the right most Controller is used as the MAIN LINE reversing switch.

For what it is, the Atlas system works fine, you just need to set it up correctly and know what each switch does and know which ones to leave alone.

And maybe, you need to accept the established conventions of MAINLINE and REVERSE LOOP?

IMPORTANT - the Atlas system, and common rail in general, will not work with dual power packs fed from a single internal transformer. You will get a short when you hook up the common wire and reverse the direction of one throttle in relationship to the other.

Over the years many better dual packs actually had separate internal transfomers because common rail was popular back in the day.

You must have a separate transformer (derived source) for each throttle to use common rail for multi train cab control.

For those who don't undertand this, I will explain transformer theory and why you don't get a short with two separate power packs some other day.

Meanwhile, I am working on a best design for the OP's track plan.....

Sheldon 

 

    

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Posted by CSX Robert on Sunday, June 13, 2021 9:51 AM

Lastspikemike
Did we also verify that, assuming the two power packs depicted by Atlas are identical, that Atlas shows the positive and negative outputs connected incorrectly to the 220? If yiu connect as shown you will get a dead short.

No we did not verify that because it is not true.

Ignoring the cab selector and reversing switch for the reversing (X-Y) section, ther Eare five settings for 220.

The first setting has both cab revresing switches set to the middle position.  It connects the cab A and B inputs directly to the right hand side outputs and leaves the C terminal unconnected (Edit: I meant to point out in that anything marked in yellow in these diagrams is unconnected):

202

Here are the other four combinatons (I've labeled the switch postions up and down to match the schematic even though physically they are left and right) :

 Up-up

Up-down

 Down-up

Down-down

For each cab and each position, one input is connected to the outer (upper cab A, lower cab B) output terminal for that cab, the other input is connected to the common terminal, the inner output terminals are left unconnected, and there are no shorts anywhere.

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Posted by SeeYou190 on Sunday, June 13, 2021 10:03 AM

I do not understand labelling power pack track outputs.

The track output is polarity reversable by the direction switch on the power pack. It does not have a positive or a negative.

Confused

-Kevin

Wink Happily modeling my STRATTON & GILLETTE RAILROAD. A Class A line located in a personal fantasy world of semi-plausible nonsense on Tuesday, August 3rd, 1954.

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Posted by Lastspikemike on Sunday, June 13, 2021 10:14 AM

Well, I'll check it again someday. At the moment both my view of the schematic, my testing with my multi meter and my experience wiring ganged 220 say otherwise. I wired ours up wrong and they didn't work. Wiring them correctly, not as shown by Atlas, worked. But then I was connecting a MRC 780 twin throttle powerpack to the 220's.

DC powerpacks have positive and negative output terminals or they wouldn't need a reversing switch to operate trains. Multimeters display reversed polarity, digital with a minus sign and analogue by driving the needle backwards. 

I still say that because the C terminal has to feed the reversing section terminals and that only one polarity reaches the block selector switches that it matters which way around the four input terminals on the 220 are connected to the two powerpacks. But I'm no electrical genius so I may be mistaken. 

Heck I still think all the Cabs must have the same polarity terminal connected to the common rail.....

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Posted by Lastspikemike on Sunday, June 13, 2021 10:22 AM

CSX Robert

 

 
Lastspikemike
Did we also verify that, assuming the two power packs depicted by Atlas are identical, that Atlas shows the positive and negative outputs connected incorrectly to the 220? If yiu connect as shown you will get a dead short.

 

No we did not verify that because it is not true.

Ignoring the cab selector and reversing switch for the reversing (X-Y) section, ther Eare five settings for 220.

The first setting has both cab revresing switches set to the middle position.  It connects the cab A and B inputs directly to the right hand side outputs and leaves the C terminal unconnected:

202

Here are the other four combinatons (I've labeled the switch postions up and down to match the schematic even though physically they are left and right) :

 Up-up

Up-down

 Down-up

Down-down

For each cab and each position, one input is connected to the outer (upper cab A, lower cab B) output terminal for that cab, the other input is connected to the common terminal, the inner output terminals are left unconnected, and there are no shorts anywhere.

 

Thanks for doing that. 

The two "up down" coloured schematics seem to show the short circuit I refer to. The opposite polarities of the powerpacks connect at the Common terminal. That looks to me like a dead short. Why is it not?

Also, if you do colour in the reversing section power flow you can't get positive and negative power to that circuit unless you reverse one pair of the input  connections. The Cab selector switch would connect negative to positive, a dead short.

Does it make a difference if you gang two or more 220 together and show the polarity of current flow across the 220's with the main reversing switches at center off?

Common terminal power has to connect to the reversing section outputs for each 220 even if the main reversing switches are set to center off the Common rail  current flow comes back to that set of terminals in order to separately control the polarity of the reversing section (Wye or TT).

The first version of the 220 had no flow through for the Common terminal so this situation could not arise. 

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Posted by Overmod on Sunday, June 13, 2021 11:04 AM

Lastspikemike
I wired ours up wrong and they didn't work. Wiring them correctly, not as shown by Atlas, worked. But then I was connecting a MRC 780 twin throttle powerpack to the 220's.

Remember what Sheldon said a little earlier

IMPORTANT - the Atlas system, and common rail in general, will not work with dual power packs fed from a single internal transformer. You will get a short when you hook up the common wire and reverse the direction of one throttle in relationship to the other.

If I recall correctly the 780 is one of those with a common primary and the equivalent of two taps to supply the two 'cabs'.

I think it's time for 'chapter 2' of the explanational posts, about how the various DC devices actually work (and, in some cases, fail to work as expected).

 

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Posted by gregc on Sunday, June 13, 2021 12:07 PM

sorry.   it seems i'm just adding to the confusion

CSX Robert
gregc
the arrow is confusing in the controller schematic (upper right). there is a permanent connection between the screw terminals.   I verified this with a multimeter with the reversing switches centered.    they've confusingly drawn the connection going thru the switch.

you're right, i'm wrong, there is no direct connection between the cab reversing switch and the output terminals (right side) 

the cab A screw terminals on the right side go thru the cab reversing switch, allowing the polarity on the right side terminals to be reversed.

CSX Robert
  The other two positions connect one leg of the corresponding cab to the outer output terminal (top terminal for cab A and bottom terminal for cab B) and the other leg to the common terminal.

i believe you're saying that the cab-A reversing switch also connects the C (common) terminal at the top of the controller to bottom cab A screw terminal on the right side.   the top cab A screw terminal on the right side is the non-common rail connection

CSX Robert
 
gregc
and yes, if the plastic cab reversing switch is in the middle, there is no connection between common rail terminal, C, power pack.   The switch should not set in that position

The switch is supposed to be set in that position on all but the right-most controller when there are two or more.

ATLANTIC CENTRAL
The cab reverse switches on the ADDITIONAL Controllers must remain in the center pass thru position on those controllers.

the center position (there are no detents) disconnects the ride side terminals from the input side on the left .   the left position is a pass thru, the right position reverses (verified with multimeter)

CSX Robert
  
gregc
the bottom diagram also indicates that the common rail connection C is from the right-most 220 controller, meaning that it is the result of passing thru several cab reversing switches on one or more 220 controllers as well as the throttle itself.

The common does pass through all of the controllers (on the cab inputs/outputs), but you cannot pick it up until the last one because you cannot determine which leg of each cab is common until after the reversing switches in the last controller.

that's what the diagram shows

ATLANTIC CENTRAL
Only the right most Controller is used as the MAIN LINE reversing switch.

i agree because any other would also reverse the polarity going to the X-Y reversing switch

Lastspikemike
Did we also verify that, assuming the two power packs depicted by Atlas are identical, that Atlas shows the positive and negative outputs connected incorrectly to the 220? If yiu connect as shown you will get a dead short. 

why?

for separate cabs there are no common connections between the cabs unless one output is connected to AC ground

Lastspikemike
DC powerpacks have positive and negative output terminals or they wouldn't need a reversing switch to operate trains.

of course the output i DC.  the reversing switch is between the output terminals and the circuit inside controlling the output voltage.   that is why polarity is not marked on the output terminals.

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Posted by Lastspikemike on Sunday, June 13, 2021 12:17 PM

Well. I'll be darned. Right and wrong at the same time.

Now I understand why my particular arrangement "worked funny". The MRC 760 we connected as a third Cab to run the yard (waste of a powerful throttle that was) never could play nice with the 780. Interesting sparking effects over our Peco diamond crossing and the voltage problem Mel kindly warned me about at one Electrofrog turnout, which we solved by gapping properly and making sure the blocks were always switched properly for through trains.   

When we moved the layout I connected the MRC 760 to Cab A and the second throttle of the MRC 780 to Cab B on the 220 gang. Now the 780 is performing a more usual function of running the mainline from one throttle and the yard from the other. The yard Cab doesn't need to go through the 220. The MRC 760 connects to the whole layout through a 215 selector switch which treats the entire yard as a block from the 760 operator's perspective all the Cab A yard block switches are connected through the one block switch in series with the 220. Cab B connects to all the yard blocks through that same single selector switch. 

Originally, I couldn't quite figure out the wiring I now use. I still can't figure out how to connect three Cabs to the entire layout using the 220 to control reversing sections. We used to have three reversing sections but we now realize you only need two maximum for any layout, to be able to run  any train in either direction anywhere. 

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 12:21 PM

Lastspikemike

Well, I'll check it again someday. At the moment both my view of the schematic, my testing with my multi meter and my experience wiring ganged 220 say otherwise. I wired ours up wrong and they didn't work. Wiring them correctly, not as shown by Atlas, worked. But then I was connecting a MRC 780 twin throttle powerpack to the 220's.

DC powerpacks have positive and negative output terminals or they wouldn't need a reversing switch to operate trains. Multimeters display reversed polarity, digital with a minus sign and analogue by driving the needle backwards. 

I still say that because the C terminal has to feed the reversing section terminals and that only one polarity reaches the block selector switches that it matters which way around the four input terminals on the 220 are connected to the two powerpacks. But I'm no electrical genius so I may be mistaken. 

Heck I still think all the Cabs must have the same polarity terminal connected to the common rail.....

 

As Kevin pointed out, the reverse switch on the power pack changes the polarty of the output terminals, so there is no plus or minus terminal.....

Your last statement about common rail and polarity does make it clear you are not an electrical genius and that you don't understand transformer theory or DC theory.

Hooked up as intended, and used as intended, the Atlas system works fine.

BUT you cannot use dual packs with a single internal transformer as I stated above, and you need to follow various established conventions regarding reverse sections and common rail.

Use whatever terms you want Mike, but if you want people to understand you, there may be an advantage in using already established terms and definitions......

I power my signal system, cab selector system and switch machines with a multi phase dual voltage power supply that supplies both 24vdc and 12vdc. The first thing you do to build such a system is connect the positive terminal of one DC power supply to the negitive terminal of another DC power supply...... simply magic.

Keep this in mind, electricity is magic, you have never seen it, you have only seen what it can do.......

Sheldon

    

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Posted by Lastspikemike on Sunday, June 13, 2021 12:24 PM

I know assignment of polarity of the main powerpack is arbitrary but that's not the same thing as there not being plus and minus.

Another aspect of the way ours was wired is to have the reversing switches all set to the same direction for the same train direction.

Anyway, it appears that my particular situation related only the the internal wiring of the MRC 780 which did not show on the schematics so usefully provided in this thread.

Thanks. I believe I now understand. In effect, the MRC 780 does assign polarity but only internal to the powerpack. MRC seems not to mention this as far as I can see. 

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 12:32 PM

Lastspikemike

Well. I'll be darned. Right and wrong at the same time.

Now I understand why my particular arrangement "worked funny". The MRC 760 we connected as a third Cab to run the yard (waste of a powerful throttle that was) never could play nice with the 780. Interesting sparking effects over our Peco diamond crossing and the voltage problem Mel kindly warned me about at one Electrofrog turnout, which we solved by gapping properly and making sure the blocks were always switched properly for through trains.   

When we moved the layout I connected the MRC 760 to Cab A and the second throttle of the MRC 780 to Cab B on the 220 gang. Now the 780 is performing a more usual function of running the mainline from one throttle and the yard from the other. The yard Cab doesn't need to go through the 220. The MRC 760 connects to the whole layout through a 215 selector switch which treats the entire yard as a block from the 760 operator's perspective all the Cab A yard block switches are connected through the one block switch in series with the 220. Cab B connects to all the yard blocks through that same single selector switch. 

Originally, I couldn't quite figure out the wiring I now use. I still can't figure out how to connect three Cabs to the entire layout using the 220 to control reversing sections. We used to have three reversing sections but we now realize you only need two maximum for any layout, to be able to run  any train in either direction anywhere. 

 

ALL of this is exactly why I have little use for conventional power packs, and less use for the Atlas system.....

EVERY DC layout will have a different best solution based on track plan and operational goals.

There is no GOOD "one size fits all".

I have not seen your track plan since you refuse to post drawings or pictures, I have limited understanding of your goals. So I will not presume to know what is best for you.

But I feel fairly confident that when you offer others advice on this topic, it is HIGHLY colored by you own view on what the goals are, and your own experiance meeting your goals.

Respectfully, my experiance has bit more depth, being both an electrical designer who has designed many DC systems for many layouts and having spent years behind the shop counter helping other modelers, so I don't presume to know what others need or want until I am told so.

Sheldon

    

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Posted by tstage on Sunday, June 13, 2021 12:35 PM

ATLANTIC CENTRAL
Keep this in mind, electricity is magic, you have never seen it, you have only seen what it can do.......

You have if you've watched a good lightning storm...or the original Frankenstein movie.

https://tstage9.wixsite.com/nyc-modeling

Time...It marches on...without ever turning around to see if anyone is even keeping in step.

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 12:42 PM

Lastspikemike

I know assignment of polarity of the main powerpack is arbitrary but that's not the same thing as there not being plus and minus.

Another aspect of the way ours was wired is to have the reversing switches all set to the same direction for the same train direction.

Anyway, it appears that my particular situation related only the the internal wiring of the MRC 780 which did not show on the schematics so usefully provided in this thread.

Thanks. I believe I now understand. In effect, the MRC 780 does assign polarity but only internal to the powerpack. MRC seems not to mention this as far as I can see. 

 

The Atlas instructions clearly tell you not to use the reverse switch on the power pack - common sense might suggest putting them all in the same position, checking output polarity, and wire the whole system consistantly.

YOU just repeated in different words something I have been saying to you for months and you kept ignoring or challenging - the idea that the direction switch position should be consistant with direction of travel.

I am working on a solution of this OP, and if I have time over the coming week, maybe like my thread about trucks, I will develope a DC Primer, because it seems many who never really used DC to run their trains have very little understanding of its basic principles.

Sheldon

    

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 12:55 PM

gregc

 

ATLANTIC CENTRAL
The cab reverse switches on the ADDITIONAL Controllers must remain in the center pass thru position on those controllers.

 

the center position (there are no detents) disconnects the ride side terminals from the input side on the left .   the left position is a pass thru, the right position reverses (verified with multimeter)

 
 
ATLANTIC CENTRAL
Only the right most Controller is used as the MAIN LINE reversing switch.

 

i agree because any other would also reverse the polarity going to the X-Y reversing switch

 

 
 

I'm going by the drawing and memory, I don't have one here to test. I sold them to a lot of people, I helped friends wire them years ago, but I never used one on my layout. I had real toggle switches, even at age 12......

They show three positions on the diagram? The instructions clearly say "center position"?

Does not matter, fact remains on intended operation as I described, all additonal Controllers to the left for additional reverse sections should have their cab reverse switches NEVER used and left in whatever position provides pass thru.

Maybe with some luck today I will find my 1957 copy of the Atlas wiring book.....

Sheldon

 

    

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 1:02 PM

tstage

 

 
ATLANTIC CENTRAL
Keep this in mind, electricity is magic, you have never seen it, you have only seen what it can do.......

 

You have if you've watched a good lightning storm...or the original Frankenstein movie.

 

I know you're just poking fun, but actually no, lightning is the ionized light produced by electricity, still not the moving electrons.

As a working electrician, I make "lightning" sparks all the time on purpose. When we want to turn off a low amperage (120v, 15/20amp) circuit we are working on, we often just short it out and trip the breaker - presto, the circuit in question is off and easy to identify in the panel.

Sheldon

    

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Posted by ATLANTIC CENTRAL on Sunday, June 13, 2021 1:31 PM

Ablebakercharlie, I sent you a private message. With any luck the little word "message" to the right of your screen will be red and you can access my message and respond.

Sheldon

    

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Posted by Lastspikemike on Sunday, June 13, 2021 1:53 PM

A DC primer would be handy.

I have a common rail system in that all my red wires are connected and three throttles are connected to all the red wires ( although some of the red wires are actually white because one of our group of three worked as an electrician years ago and to him white was the hot wire). 

So, I admit to becoming confused again. Since two of the three throttles are in a MRC 780 then clearly I'm not experiencing the internal short problem. We routinely have the powerpack reversing switches opposed.

My remark about train direction was a serious remark.  We have two loops and one connecting track. The "outside rail" of one loop connects to the "inside rail" of the other loop. We can't have a consistent East West or clockwise and counterclockwise. One loop is always the reverse of the other. The connecting track has neither an inside rail nor an outside rail. No left or right rail if you prefer. 

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Posted by gregc on Sunday, June 13, 2021 1:53 PM

ATLANTIC CENTRAL
I'm going by the drawing and memory, I don't have one here to test.

i do have one and i verified it after.

any reversing switch has just to positions, if not center-off, non-reversing or "pass thru" and reversing.     ... think about it.   why would it have a pass-thru and non-reversing position?

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Posted by Lastspikemike on Sunday, June 13, 2021 2:07 PM

The 220 reversing switch has a center off but this position passes through the connection so isn't really "off".

The grey reversing section switch and the green Cab selector switch on the. 220 both have center off.  

The Twin Switch and the Selector switch both have center off. All have center detent detectable, although the selector switches are pretty vague.

The yellow connector switches are just on/off and have a more limited range of movement.

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    February 2007
  • From: Christiana, TN
  • 1,750 posts
Posted by CSX Robert on Sunday, June 13, 2021 2:10 PM

Lastspikemike
The two "up down" coloured schematics seem to show the short circuit I refer to. The opposite polarities of the powerpacks connect at the Common terminal. That looks to me like a dead short. Why is it not?

This is confusing for many people when they first look into common rail wiring.  Take for example a single 12 volt isolated power supply.  The '+' terminal on that power supply by itself is not actually +12 volts, it is +12 volts relative to the '-' terminal of that power supply.  The voltage at any single point has to be measured relative to some reference point.  With two separate isolated power supplies there is no common reference point.  With common rail cab control wiring, you are creating a common reference point - the common rail.  The control rail can be made positive or negative relative to the common rail by switching the polarity of the cab controlling that rail.

It's kind of funny in way, many people have trouble with hooking the '+' of one power supply to the '-' of another, yet most of them have done the same thing putting batteries in a flshlight without thinking twice about it.

  • Member since
    September 2003
  • 17,203 posts
Posted by Overmod on Sunday, June 13, 2021 2:12 PM

Lastspikemike
one of our group of three worked as an electrician years ago and to him white was the hot wire). 

OK, I'll bite on this.  In what retarded imitation version of the NEC or any other valid national code does 'white' denote 'hot' instead of neutral?

In part I'd like to know because I found a "professionally" wired job in Springhill where the wires mysteriously changed colors passing through a junction box.  I attributed this at the time to guild malevolence against 'outsiders' messing with electrician prerogatives (NEC's position being no colors are 'official' and you should always check before tinkering anyway) but perhaps this is some distinctive color aberration taught to apprentices?

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