What wire gauge or rating is best dropper wire?

[Chrissaf]

7/0.2mm wire is the optimum wire IMHO for droppers as long as the dropper is limited to max 300mm lengths.

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7/0.2mm = Seven strands of 0.2mm wire inside a common PVC sheath. Being stranded is better than solid wire as it is less prone to fatigue induced breakages. It is thick enough for a few amps of current [more than enough for model railway sections of tracks], but thin enough as to be easily hidden by ballast where soldered to rails. It solders to Nickle Silver rails very easily too.

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Remember that as there are multiple droppers, the current flow from the controller to the locos is distributed between them, so no single dropper needs to take the full layout current consumption.

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The 300mm long droppers then connect to the main power distribution BUS wires under the basboard made from 32/0.2mm wire, that does carry the full layout current load.

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Others will have other opinions ... but the above are mine, and has been used with my Elite since 2013 without issue.

[Railway man 123]

Why is it limited to 300mm and what is the difference between bus and dropper cable and what bus cable would you use. 

[Chrissaf]

Why is it limited to 300mm

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300mm to minimise any possible voltage drop. Being thinner wire, it will have a finite amount of resistance. Pass a current through a resistance and you generate a voltage drop.

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what is the difference between bus and dropper cable

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The names actually tell you their function. The 'dropper' is a short light weight cable to drop down from the track rails to the main BUS underneath the baseboard. In this context, BUS is just a generic term, rather than a literal interpretation of the busbar function described in the following clickable link. The BUS cable is the much thicker cable used to distribute (busbar) the power around the layout under the baseboard. Being thicker it can handle the electrical currents over longer distances with minimal voltage losses.

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what bus cable would you use.

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I actually stated that in my first reply 32/0.2mm cable [32 strands of 0.2mm wire contained within a single PVC insulating sheath].

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[Chrissaf]

I have a rather big 2 loop railway one just a loop and one a L shaped loop. I want to be able to prepare wagons and carriages In the sidings while running as normal on the loops. I am running the elite. And I think I will solder the wire to the track but what wire would you use? I believe what I'm looking for is dropper wire and it needs to carry 15v from elite. Any help would be great Many thanks.

[Flashbang]

Hi

7/.0.2mm dropper wire is fine, so long as virtually all, if not all, sections of track have a pair of droppers fitted and are not longer than approx 300mm rail to bus wire.

You need you understand it is the fault current that needs to get back to the console as fast as possible to cause a cut off of track power that is vitally important.    If you can't fit droppers to every section of track then consider increasing the dropper wire size to 16/0.2mm.

The bus size of wire needs to be able to pass the maximum fault current. Hence the minimum recommended wire size is 32/0.2mm or 1.5mm2 solid.  Larger wire sizes for the bus pair will never hurt.

 

An the Elite has a 4.0Amp power supply which means that roughly 5 tor perhaps more Amps will have to flow as a fault current to cause the overload trip to operate. The overload device must operate as fast as is possible, hence the larger bus wire size. As a larger wire size passes more current very quickly!

Failure of the DCC consoles overload device to operate will result in large currents flowing, which the rails and pointwork is not designed to pass, should only a few droppers be used.  Remember that 15 volts DCC at 4.0 Amp is 60 watts.  That is 60 watts minimum and is equal to a 60 watt lamp being lit which is incredibly hot! Volt drop in the bus pair on large layouts using undersized bus wires causes slower tripping times too!   

Always test the time from applying a short across the rail to the time the console trips and removes power. It should always be almost instantaneous!  Use the momentary "coin across the rails" test to prove all is 100% 

[Railway man 123]

Why is it limited to 300mm

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300mm to minimise any possible voltage drop. Being thinner wire, it will have a finite amount of resistance. Pass a current through a resistance and you generate a voltage drop.

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what is the difference between bus and dropper cable

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The names actually tell you their function. The 'dropper' is a short light weight cable to drop down from the track rails to the main BUS underneath the baseboard. In this context, BUS is just a generic term, rather than a literal interpretation of the busbar function described in the following clickable link. The BUS cable is the much thicker cable used to distribute (busbar) the power around the layout under the baseboard. Being thicker it can handle the electrical currents over longer distances with minimal voltage losses.

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what bus cable would you use.

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I actually stated that in my first reply 32/0.2mm cable [32 strands of 0.2mm wire contained within a single PVC insulating sheath].

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Thank you so much I will use the wires you specified this was a great help

[Chrissaf]

Railway man 123,

Please try and avoid using the 'Blue Button' it just duplicates the previous replies unnecessarily. Particularly long ones like mine. TIPs 2&3 will tell you how you can use the 'Blue Button' more successfully by editing out the erroneous text.

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For future reference please note the text below:

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TIP: As a newbie poster on the forum, just be aware that the 'Blue Button with the White Arrow' is not a 'Reply to this post' button. If you want to reply to any of the posts, scroll down and write your reply in the reply text box at the bottom of the page and click the Green 'Reply' button.

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See also – further TIPs on how to get the best user experience from this forum.

https://www.hornby.com/uk-en/forum/tips-on-using-the-forum/

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[Railway man 123]

Ok I will hit the green one in future :-). Can I use the power track for the loop and droppers for the sidings or do you have to do droppers on every bit of track. Many thanks

[Chrissaf]

Personally, I have droppers on every single individual piece of track including points. So that nowhere is the transfer of electrical current reliant upon a mechanical track joiner. The track joiners are just relegated to aligning and joining the rails physically. But there again, even I would consider that to be overkill.

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For me, I use PECO SL track, so apart from the points and diamond crossing, all my track is 36" lengths of flexi-track. So that does somewhat reduce the number of droppers required compared to Hornby set-track. And thus more manageable to implement.

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I don't use PECO's version of the Hornby power track / power clip either. I personally consider these PECO / Hornby clip on power connections a fault liability in the longer term.

[Railway man 123]

Ok thank you I will do droppers on every track. :-)