# Twisted Bus Wire



## RonK9977 (Oct 4, 2019)

Hello!
My question is is do I have to twist my bus wires under my 16x4 layout...I see some people do this yet on many videos I see many do not as well...

thanks
Ron


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## gregc (Apr 25, 2015)

not the dcc track bus, certainly not for your size layout


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## RonK9977 (Oct 4, 2019)

*OK thanks*



gregc said:


> not the dcc track bus, certainly not for your size layout


OK I guess I won't have to worry about that then Thanks...It's not that large of a layout but it is 2 sheets of ply and N scale so big enough lol  

I won't wind them around themselves then 
Ron


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## Shdwdrgn (Dec 23, 2014)

Is there a purpose for twisting the wire? I've always seen the main bus lines laid in parallel, or even separated to either side of a supporting frame.


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## BrokeCurmudgeon (Feb 8, 2016)

Shdwdrgn said:


> Is there a purpose for twisting the wire? I've always seen the main bus lines laid in parallel, or even separated to either side of a supporting frame.


It doesn't matter for DC. But twisting them will act as a choke and curtail spurious pulses from effecting the bus. Although it doesn't matter, I would twist just to be safe. Just my opinion though.:laugh:


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## gregc (Apr 25, 2015)

Shdwdrgn said:


> Is there a purpose for twisting the wire?


currents are induced in loops (read separated) of wires by extraneous magnetic fields (emf). Minimizing the area of the loop obviously reduces interference. Twisting not only reduces the area of the loop but flips it over creating many loops with alternating orientation. 

Extraneous EMF in one loop with the red wire on the left cancels that in another loop with the red wire on the right. 

The phone company figured this out many years ago to minimize interference in phone lines 2 miles between a central office and house.

telephone wire is typically 4 wire with 2 twisted pairs. Ethernet cable is 4 twisted pairs.


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## Shdwdrgn (Dec 23, 2014)

Cool, thanks. Sounds like it would be a good idea for DCC then.


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## BrokeCurmudgeon (Feb 8, 2016)

Shdwdrgn said:


> Cool, thanks. Sounds like it would be a good idea for DCC then.


Not really a good idea because the twists effect the transfer of the DCC signals. That is why telephone style wire is replaced by Cat 5 and/or Cat 6. The wire should be optimized for DCC Sorry if this is confusing. I am old and beginning to lose my mind.:laugh: Maybe someone else can better explain it.


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## highvoltage (Apr 6, 2014)

BrokeCurmudgeon said:


> Not really a good idea because the twists effect the transfer of the DCC signals. That is why telephone style wire is replaced by Cat 5 and/or Cat 6. The wire should be optimized for DCC Sorry if this is confusing. I am old and beginning to lose my mind.:laugh: Maybe someone else can better explain it.


Cat 5 and Cat 6 use twisted pairs.

Two wires run in parallel can cause interference, as others have explained. However, this is mostly for long runs. The length of runs on a small layout would probably not be affected. However, I twist my bus wires together just for aesthetics, it makes for a nice, neat installation.


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## Lemonhawk (Sep 24, 2013)

To twist or not twist has been discuss over and over. the rails aren't twisted, so why twist the bus? Twisting helps receivers reject common mode noise, and I'm just not sure our decoders have that type of receiver circuit.


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## highvoltage (Apr 6, 2014)

RonK9977 said:


> OK I guess I won't have to worry about that then Thanks...It's not that large of a layout but it is 2 sheets of ply and N scale so big enough lol
> 
> I won't wind them around themselves then
> Ron


I don't think he was commenting on the size of the layout per se. I believe he was referring to the fact that signals over short runs are not adversely affected if the wires are left untwisted.


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## Shdwdrgn (Dec 23, 2014)

highvoltage said:


> Cat 5 and Cat 6 use twisted pairs.


You know, it just occurred to me... I have noticed that the twists in CAT5 don't match up (slightly more/less twists per foot in each pair), and because of the discussion above it suddenly makes sense that this would be done on purpose.


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## highvoltage (Apr 6, 2014)

Lemonhawk said:


> To twist or not twist has been discuss over and over. the rails aren't twisted, so why twist the bus? Twisting helps receivers reject common mode noise, and I'm just no sure our decoders have that type of receiver circuit.


The rails are far enough apart to not affect the signal. However, in practice I twist all my bus wires just because to me it looks better.


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## mesenteria (Oct 29, 2015)

Lemonhawk said:


> To twist or not twist has been discuss over and over. the rails aren't twisted, so why twist the bus? Twisting helps receivers reject common mode noise, and I'm just not sure our decoders have that type of receiver circuit.


This is generally all that matters for smaller layouts. For truly large runs of both rails and bus, you'd be better off creating a 'shallow' helix for the bus, and possibly using a 'snubber' at the ends of the bus. But if it's truly necessary, why don't we have to wind the rails around each other as well? :dunno: In N scale, they run just a fraction of an inch apart, and on large layouts that may mean tens of feet. No problems ever reported.

This has been discussed at length across numerous forums for years, now that DCC is nearing 25 years of common usage. For bus runs less than 25 linear feet, winding is not necessary...that is the general consensus. After that, it shouldn't hurt.


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## gregc (Apr 25, 2015)

no need to twist a DCC bus. Interference is not likely to overwelm the currents being drawn by the loco and carrying the signal.



Shdwdrgn said:


> You know, it just occurred to me... I have noticed that the twists in CAT5 don't match up (slightly more/less twists per foot in each pair), and because of the discussion above it suddenly makes sense that this would be done on purpose.


doubt it. all 8 wires are used for higher speed ethernet. I don't no of anything unique about one pair vs another


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## Shdwdrgn (Dec 23, 2014)

gregc said:


> all 8 wires are used for higher speed ethernet. I don't no of anything unique about one pair vs another


What I meant was that by keeping the twists mis-matched between pairs it would also help damper any inductance over long runs.


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## gregc (Apr 25, 2015)

Shdwdrgn said:


> What I meant was that by keeping the twists mis-matched between pairs it would also help damper any inductance over long runs.


why?
what does inductance have to with it?


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