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Bus Wire size

985 Views 37 Replies 9 Participants Last post by  PAPPA.B
Hi Planning ahead my layout will be 7mx 2.7 one side will house a 10 track +18 points storage yard the other side a station, goods yard sidings and possible small engine shed. There are some 12 base boards including one a swing gate entrance and two extensions. The boards will be wired in an upright position so breaks in between the boards rather than trying to wire underneath the layout. A couple of questions I was looking at 2.5mm for the bus is this enough, the droppers 16.02 what max length should these be. With the break at the swing gate would it be better to have two separate Bus wire sections . What would be the best way to join the bus wires at the board joints? Jim
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Hi Jim, Rather odd, since it heats up the rails enough to solder, does the solder adhere to the Bus wire, if you try tinning it, without the other wire at the joint?

Ok, a few things here. Firstly, is your bus wire twisted copper strands? If it isn't copper then don't use it. With some cables the insulation, when stripped off, can leave behind a residue. Give it a bit of a clean with a bit of fine wire wool (or even a small file) before you try and tin it with solder. A bit of 2.5mm sq. copper wire can soak up the heat from the iron. Make sure you heat it up enough before trying to get the solder to stick. A hotter iron iron (set at 350/400 degC) will help but isn't essential. I find a small wedge tip better for this than a pointed tip. Use lead solder rather than lead free solder for ease of use. Multicore solder is good but you may need a bit more rosin flux on the tip of your iron becsuse the flux burns off quickly. Bend the end of your dropper wire to 90deg (about 5 to 8mm is enough) and solder it to the bus inline. You can easily solder three or four droppers to each stripped bit of bus wire. Once they are all done cover the bare wire joins with a bit of self amalgamating tape.
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Hi Thanks the help. Yes the bus wire is twisted and I did tin it but it was not sticking very well it may be that there is some residue on the wire which I bought from Maplins years ago and is bigger than the 2.5 I have just received. Which may explain things I since read somewhere the lead in the solder is better the ones I have been using are lead free. I will give this another go many thanks .Jim
Do you have any Isopropanol, or similar, to wash the exposed Bus wire, before giving it a scrub with a fibreglass cleaner / abrasive?

Thanks Julian Yes I do have Isopropanol and a fibreglass pen but never thought to clean a newly bared wire which makes sense as to why it is not sticking. I should get chance to have a go tomorrow. Almost ready to start laying track in the storage yard got to get some more Copydex. Successfully soldered the droppers to the first piece track and cut all the copper clad for the board joints. Still not sure about the attachments of the droppers to the bus wire but I will give Jamesed suggestions a go if I can do a reliable and tidy job then that's the way i'll do it. If not then I will use some T-Tap or scotch lock type fittings. I very much appreciate the help you guys have given me this what I like about the forum always someone willing to pass on there experience and knowledge even though some of these questions must be quite trivial . Jim
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Hi The wire I ordered has now arrived . But while I was waiting for it I thought I might have a practice on some of the wire I already had . Soldering the dropper wires to the rails seemed ok . How ever trying to solder the droppers to the bus just it would not solder. Am I not using the correct solder is my soldering iron knackered? The bus wire is some that I had for my previous layout I snipped the end off so that I had a clean piece to work with I also used my new strippers to expose the wire in the centre neither seemed to work. I am using some DCC Concepts Sapphire 179 universal I also tried some solder core wire Alloy 1mm neither that didn't work either my soldering iron is an Antex 50w it is a few years old where am I going wrong? Any help much appreciated . Jim
It sound to me that you may not be 'tinning' both sides. This is a practice where you heat a part to be soldered and melt a small amount of solder onto it. Do the same to the other part. Then put the parts together and heat the whole thing. You should find it solders together quite easily. Make sure you iron is hot enough. Hotter means a quicker job.

With regards droppers, I have an article here: Power Feeding With Droppers

Please Avoid Solder Globules on Rails.
Graham Thanks for your reply I did tin both parts and used a liquid flux and while it stuck on the droppers and rail it was not so good on the bus wire and sometimes flaked off . As I've said I couldn't understand why when the the droppers were fine with the rail I have used a fibre pen or a file to give it a key and that seemed to work ok. The only thing that I did not do was clean or rub a file over the exposed bus wire. I haven't had chance today to see if that will make a difference but will have a go in the next few days. Jim
Jim, don't worry, what you describe isn't uncommon. My bus wire is 2.5mm sq 6491B which strips cleanly and providing I make sure I get enough heat into the copper wire my lead multicore solder sticks nicely to it with minimal cleaning first. I also have a 12v dc bus for accessories and lighting for which I used 2x1.5mm figure of 8 speaker wire which seemed like a good idea at the time. The insulation on this is quite sticky and leaves behind a residue. If I don't give it a good clean first I stand no chance of getting the solder to stick. A bit of IPA as suggested and a bit of wire wool will sort it out. I'm not sure the fibreglass pen will be man enough for the job (am I allowed to say 'man enough' these days???). You said that you think the wire you were initially using may have been bigger than 2.5mm. The next size up is 4mm sq and that would need significantly more heat into it for the solder to stick firm.
Yes I going to ask if the larger wire might need more heat Although now that I have the 2.5 I will do some practice with this wire. Jim
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Ok I have installed most of the 2.5 bus wire under the base boards the track for the storage yard has been laid and droppers added some 72-ish pieces of rail so a lot of droppers though as yet the droppers are not connected to the bus . But my main reason for this enquiry is I am using the NCE Powercab and the small plug that is to take the bus wire is only big enough for dropper size wire. This issue must be one that has been raised in the past. So I have used a short piece of dropper wire (100mm) connected to a choc block and the bus wire. To me who has a very limited knowledge this doesn't seem right but I do not know what other method I could use any help welcome. Cheers Jim
Some pictures

hope this helps explain . Jim
Hi Jim,
Being an electrician (or ex electrician now), I would assume the larger size of the bus wire is because of the length of its run, (to prevent too much volt drop)
A shorter length to connect to the bus should be fine.
Hi Alan Thanks I did wonder though I was concerned it may get hot but because it is short it might be ok. The fact that the plug only takes a small wire just seemed a little odd. Cheers.Jim
I don't know what size your dropper wire is but it's likely that you'll find the connector will take something bigger albeit not as big as your 2.5mm sq bus wire. Try a bit of 1mm sq or even 0.75mm sq wire. Providing it's only a very short length it should be absolutely fine, especially if you use the biggest you practically can. However, I don't like the look of those screw terminals for joining the bus wire. Maybe use Wago connectors instead. A screw terminal connection will degrade over time as the copper compresses and then oxidizes. If you really are committed to using them, go around once a week with a screwdriver and make sure they are tight, even if it's a quarter turn that will make a difference. Sprung connectors, like Wagos, maintain the pressure on the copper wire even if there is some compression so you are less likely to get oxidixation and increased impedance.
Dcc Concepts Twisted 1.0 Bus Wire certainly fits and has some room to spare, so their TW 1.5 might well also fit.

Thanks for the replies I find wire descriptions confusing the 2.5 DCC Concepts bus wire is 3mm in diameter including the casing the dropper wire is 2mm there are some some numbers on these item packaging (DSW-RD25-2.5) and (RCA-RBW.5) . Previous wiring I had bought described as 24/0.2 ect. which I sort of understood and looking at connectors equally I find confusing . You mentioned using Wago connectors so I looked them up and it stated they can be used up to 4mm wire which I take as the overall diameter of the wire they are not cheap but then I don't mind paying for something if I can use it . I recently bought some T-Tap connectors only to find the the bus wire was to large to fit these being described as 22AWGcable0.2-05mm sq.:unsure: The screw terminals do have a clear plastic cover however the sides are obviously open . I will try some of the 24.02 wire to see if it will fit in as this is thicker than the dropper wire currently fitted I will also get some Wago connectors. Many thanks for all replies . Jim
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24/0.2 is equivalent to 0.75mm sq. cross sectional conductor area cable. That should be fine for the links between your controller and your bus wire. Just keep them short, between 150mm and 250mm ideally, and cable tie the two wires together to avoid a gap between the wires which can cause inductive field interference.

Wago connectors are great and they work just as well for small size wires as bigger sizes. Look for the newer type Wago 221 connectors. Toolstation is a good place to buy these at a reasonable price, especially in larger quantities. For example: Toolstation
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