AdeRail Posted August 27, 2017 Share Posted August 27, 2017 Hi everyone, Ive been fiddling with my dcc bus and I'm wondering if this bus wire really has to be a twisted pair?As when it's twisted and fixed under the baseboard I'm going to find it very hard to strip it and solder the drop wires to it... can it just be loosely twisted or would this defeat the object? I know you can put snubber thingies on the ends but most places say they should be twisted.. Confused Link to comment Share on other sites More sharing options...
walkingthedog Posted August 27, 2017 Share Posted August 27, 2017 Don't bother with twisting it, like you say it defeats the object of making wiring easy. Just keep the two wires a few inches apart. Link to comment Share on other sites More sharing options...
AdeRail Posted August 27, 2017 Author Share Posted August 27, 2017 Really! This would be great, but I worry about the length of these cables on my layout. If i wired straight round the middle of my boards that powers the track it would be about an 11 meter length, times this by two with the other wire and I have 22 metres, if I run a second bus parallel to this which all my points are connected to, (so I can easily disconnect these two bus' and future proof myself and maybe run two controllers in the future), then that gives me 44 metres... Wouldnt I get Voltage drop with all this If they weren't twisted? Link to comment Share on other sites More sharing options...
Rog RJ Posted August 27, 2017 Share Posted August 27, 2017 Voltage drop has nothing to do with the cables being twisted together or not. It is purely due to the resistance of the wires and that stays the same whether the wires are twisted together or not. Link to comment Share on other sites More sharing options...
AdeRail Posted August 27, 2017 Author Share Posted August 27, 2017 Ok maybe voltage drop isn't the right thing I meant, aargh I'm always getting things mixed up 😬. maybe I'm thinking about corrupted dcc signals or something. Link to comment Share on other sites More sharing options...
Fishmanoz Posted August 27, 2017 Share Posted August 27, 2017 WTD, this is another instance where the simplicity of wiring for DCC isn't. Twisting is desirable for longer DCC buses to proof against interference being picked up and corrupting the DCC signal. This topic has been covered extensively on the forum previously, not for at least a few months though. Do a forum search or someone like Chris will be along soon to reference it for you. Or or try this link to Mark Gurries who has been referenced before and done the engineering on it: https://sites.google.com/site/markgurries/home/dcc-general-best-practices/wiring-planing Link to comment Share on other sites More sharing options...
Chrissaf Posted August 28, 2017 Share Posted August 28, 2017 Rather than replicating a whole lot of theory on twisted pair vs not twisted pair wiring that is already on this forum somewhere. I direct you to a different page on Mark Gurries excellent DCC site (to the one Fishy has provided a link for)..I am in the DCC Twisted Pair design camp. Just because something works (parallel wire wiring), doesn't necessarily mean that it is 'best engineering practice'. Perfectly OK for small layouts and short Bus runs, but at the distances you are describing, I personally, would future proof myself and go with a twisted pair Bus. If the twists are done to the spec given by Mark Gurries I don't see connecting droppers as a significant insurmountable issue..https://sites.google.com/site/markgurries/home/dcc-general-best-practices/wiring-planing/twisted-pair-wiring.EDIT: Note that Mark Gurries is a member of the NMRA, the technical body that writes the DCC specification standards. Straight from the 'horses mouth' so to speak. Link to comment Share on other sites More sharing options...
2e0dtoeric Posted August 28, 2017 Share Posted August 28, 2017 Slightly o/t - worried about voltage drop on a long run? Easy fix - use thicker wire!Picture a firemans hose v/s a thin little garden hose. Same pressure, but which has the bigger flow? (That's a very crude analogy, but it works). Link to comment Share on other sites More sharing options...
AdeRail Posted August 28, 2017 Author Share Posted August 28, 2017 Well I haven't been running anywhere 😎 I think I read somewhere that you count the length of the cables as singular, so if you have 11 metres of red you double it when you add the black... I may be wrong.. Mark G states 10 metres as the maximum length before twisting so you can see why I am confused.. Link to comment Share on other sites More sharing options...
Chrissaf Posted August 29, 2017 Share Posted August 29, 2017 I think I read somewhere that you count the length of the cables as singular, so if you have 11 metres of red you double it when you add the black... I may be wrong..You treat the Bus length as a pair. Link to comment Share on other sites More sharing options...
RDS Posted August 29, 2017 Share Posted August 29, 2017 I twisted mine for 2 reasons:1) I read about it on here at the time (probably a couple of years ago)2) It kept my wiring together. I had no difficulty attaching the droppers by just untwisting it locally slightly. Link to comment Share on other sites More sharing options...
walkingthedog Posted August 29, 2017 Share Posted August 29, 2017 How many twists should there be per yard/metre. I would think just a couple and not a continuous tight twist. Link to comment Share on other sites More sharing options...
Chrissaf Posted August 29, 2017 Share Posted August 29, 2017 I would agree. I have seen it in print somewhere, but can't recall where. I think it was something like one or two twists per foot. Link to comment Share on other sites More sharing options...
walkingthedog Posted August 29, 2017 Share Posted August 29, 2017 Maybe newcomers think it should be tight making attaching droppers very difficult. Link to comment Share on other sites More sharing options...
Bulleidboy Posted August 29, 2017 Share Posted August 29, 2017 My "bus" was installed by passing it (the wires) through the holes in the cross-members. Also being single core cable it was fairly thick (2.5) and not the most manageable item, but as it was installed loosely there was a fair bit of slack between the two wires. Having read about "twisting), I just stuck a small screwdriver between the two wires and twisted them together. I still had plenty of room for droppers. Has it made a difference - who knows. I do have "bus terminators(?)" fitted and both ends of the wires - these came from DCC Concepts. Link to comment Share on other sites More sharing options...
AdeRail Posted August 29, 2017 Author Share Posted August 29, 2017 This is the site where it states 3 twists per foot. http://www.wiringfordcc.com/track_2.htm#a49 However twisting and threading twin and earth cable through the holes in the cross members of my baseboard is proving quite difficult at the moment... getting my legs stuck in the long cable as I twist them, plus tangling and swearing and banging my head, to name just a few difficulties 🫨 Link to comment Share on other sites More sharing options...
Fishmanoz Posted August 30, 2017 Share Posted August 30, 2017 And that site is referenced in the Mark Gurries link Chris gave you so it can be relied upon. Link to comment Share on other sites More sharing options...
morairamike Posted August 31, 2017 Share Posted August 31, 2017 I use mains 2.5mm cable stripped out of the outer sheath. On each length of 6 ft run. At strategic intervals tag strip boards are inserted through which the bus wires run. these are no less than 6 inches apart and no more than 18 inches. From these tag strips the feeders are run, these are 7/0.2 cables. These are soldered to the mid point on each rail piece irrespective of their length. The bus is twisted once between the tag strips. Across board joins the 2.5mm cables are routed through 25 way "D Type" plug and sockets. To ensure good contact in the D Types each cable in the bus passes through two adjacent pins. Some will see this as as an overkill, but in the 5 yyears of my last layout i never suffered a rail supply failure Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.