A primer on wire sizes

Using the right wire for a model railway will not only be cheaper it’ll make the wiring easier. But what are the right sizes of wire to use.

When wiring a layout for the first time, many railway modellers just grab the first bits of wire that we have to hand.

But that’s an expensive and cumbersome way of wiring a layout.

Don’t forget that along with the wire itself, you’ll also need switches, connectors and sockets and maybe heat shrink tube wrap to go with them and the costs for these mount up as the sizes of cable and wires increase.

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Summary:

Bus Wires
	Small layouts	1.29mm diameter  – 18 gauge
	Medium layouts	1.62mm diameter – 16 gauge
	Large layouts	2.5mm diameter – 14 gauge
Dropper wires		0.64mm – 23 gauge

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And then there’s the flexibility of working with wires.

Different types and sizes of wires behave differently when being bent and soldered. Using the wrong type can make what should otherwise be quick wiring jobs problematic and tiring. If you don’t have a good wire stripper for example removing the insulting sheaf from very thick or very thin wire can be slow going when you have a lot to do.

And let’s not forget the biggest problem, using the wrong wire sizes can create electrical problems around the layout with insufficient current being getting the track, point motors and lights for them to work.

Getting the right wire size then makes constructing the layout easier, cheaper and results in a more reliable model railway.

Lucky for you I’ve written this handy guide on model railway wire sizes just for MRE 🙂

Track bus wiring sizes

For the bus wiring, there are three recommended sizes dependant on the size of your layout.

For small layouts, 8ft by 4th and below, 1.29mm diameter wire (18 SWG or 16 AWG) gauge is more than sufficient.

For medium sized layouts, up to 12ft by 16ft, 1.62mm wire (16 SWG, 14 AWG) gauge is recommended while for layouts with long track runs, club layouts etc, 2.5mm (14 SWG / 12 AWG)  is what I would use.

Best wire for dropper wires and track feeders

Feeders, aka droppers, should only be a few inches long so smaller gauges – 23 SWG or 0.64mm (22 AWG) – is more than enough. The size is also much easier to work with when soldering to the rails.

On the subject of dropper wires, I recommend droppers for each section of rail.

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Note: For all of the above, you can use larger grades of wire than recommended above, using number 14 for small layouts for example, and if that’s all you have available then it’s fine. However remember that you’ll need to solder or connect the wires to often small contacts around a layout, such as N or OO/HO track rails, and it can be a challenge soldering heavier gauge wire to rails for example.

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Solid or stranded wire – which is best

There’s endless debate about whether stranded or solid core wires are better for model railways. Some argue solid core is easier to solder to rails; others that stranded wire is more suitable as its more tolerant when bent around tight corners of a baseboard – such when coming down from the rails and bending under the baseboard to meet a bus wire.  And then others argue it’s easy to solder solid core.

Personally, I stick by a simple rule of thumb I learnt on a college electrical course many many years ago and which is just as appropriate for model railways. If the wire run you’re working on is fairly straight, doesn’t have sharp bends and will rarely move, solid core is best. But if you’ll be bending, twisting or moving the wires around a lot, stranded is the way to go. The logic for this is that solid core is easier to break or damage when being moved, whereas stranded wire is more flexible and easy to bend and more tolerant of being manipulated.

Although solid is cheaper, I now tend to just use stranded wire for all applications given its flexibility and will be less prone to break, if (when!)  I change the layout and need to move the wiring around.

Wire gauge, as mentioned throughout this guide, a measurement of wire diameter with the largest wires having the lowest number. A comparison of the old British SWG – BS3737 – scale, American AWG and the modern IEC 60228 scale is given here). For model railways, wires used are in the range

What colour wire to use on a layout

Any colour you want. Simple.

The colour of the outer sheaf of wire has no meaning to the physical properties of the conducting metal inside and as such you can use any colour wire you chose.

A good rule however is to have consistent colouring, so the same colour is used for the same sort of wiring around the layout. On my layout, DCC bus wiring and track feeders are always Red and Black; DC wiring for accessories is brown and yellow; point frog wires are green etc.

With consistent colouring, I can avoid hang-slapping episodes of connecting DCC track to DC wires and then spending hours trying to figuring out why my trains don’t run or worse. Life is too short.

Hopefully, this quick guide to the wire to use on a model railway layout has given you the information you need to start wiring.

As a last bit of advice, always label the start and end of your cable runs.  Like wiring colour there are rules about this but I can say from experience it will make things much easier and reduce frustrating mistakes in the future if you do this right from the start.

For supply of bus and dropper wire and other electronic components on model train layouts, I can recommend RapidOnline as a reliable, low cost, supplier.

> A final, personal, note: I spend a huge amount of time testing, photographing, writing and researching techniques for these articles and pay for all the running costs of MRE out of my own pocket. If you found this article useful you can support me by making a donation on my fund-raising page. Thanks and happy modelling, Andy.