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DCC Layout Bus Wiring Size


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I have just obtained two 100m reels each of Gaugemaster red and black 7x0.2 Layout Wire (BPGM11) intended to be the DCC bus wires of a layout I am beginning, which will be operated on a Sig-na Trak ACE2 5A DCC system. It is much thinner than I was expecting and having read on here that some people actually use thick 15A household wiring cable for a DCC bus, I'm concerned that I have bought wire that is inadequate for the purpose. I'm not knowledgeable about electrical principles, so before I go too far, could anybody please confirm whether the wire I have is suitable for the job or not? Many thanks. Lichfeldian

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7x0.2 is good for droppers but not anywhere large enough for bus wires. 

 

How large is the layout planned to be?

 

Andi

Edited by Dagworth
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It’s all down to current carrying capacity. 7/0.2 wire is rated at between 1 and 2 amps, depending who you ask. A 4mm loco with sound could be about 1 amp so that means the safe maximum is 2 loco. In larger scale the current draw will be greater. As noted above it all depend on the size of layout and number of locos. Also locos which are not moving but have sound on will draw current. In addition a long run of 7/0.2 will suffer voltage drop, so it’s not suitable except for micro layouts. 

 

 

 

 

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1 hour ago, Lichfeldian said:

I have just obtained two 100m reels each of Gaugemaster red and black 7x0.2 Layout Wire (BPGM11) intended to be the DCC bus wires of a layout I am beginning, which will be operated on a Sig-na Trak ACE2 5A DCC system. It is much thinner than I was expecting and having read on here that some people actually use thick 15A household wiring cable for a DCC bus, I'm concerned that I have bought wire that is inadequate for the purpose. I'm not knowledgeable about electrical principles, so before I go too far, could anybody please confirm whether the wire I have is suitable for the job or not? Many thanks. Lichfeldian

 

You're using a DCC system with 5A power. It's imperative that your bus wire size is capable of handling this amount of power to all parts of the layout with minimal voltage drop. If you have a short circuit, eg when a loco derails on a set of points, then considerable damage can be done if, due to voltage drop, the full 5A does not flow and thus the DCC system sees no overload and does not cut out.

 

There are choices for bus wire - both solid and stranded - and it's really up to you. If your layout is static then I would suggest using 2.5mm "twin-and-earth" from DIY stores. Normally this costs no more than £1 per metre. Strip off the outer plastic sheath and you are left with brown and blue wires for your bus. The unsheathed copper earth wire is apparently very good for making trees!

 

When you build and wire your layout you need to make sure that you have covered the short circuit issue. Simply do the coin test - ie go round your layout and place a coin on the track and make sure the DCC command station cuts out immediately.  If it doesn't, then wiring at that point is inadequate. 

 

The wire you have (7x0.2) is fine for droppers but they need to be short - ie no more than 12-18 inches. And make sure you have plenty of them, ideally on every piece of track. 

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The layout will be a double track circuit of my attic, plus a passing loop at the station, with two sides of approx. 16' and two of 4'. There will be a goods loop leading to a goods yard/shed and sidings behind the station plus a turntable feeding a loco depot and also a short branch line. It seems as if I'm going to have a lot of spare wire, as I can't take it back now. It seems a bit of a misnomer by Guagemaster to describe it as Layout Wire, if it is not of sufficient capacity.

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4 hours ago, Lichfeldian said:

The layout will be a double track circuit of my attic, plus a passing loop at the station, with two sides of approx. 16' and two of 4'. There will be a goods loop leading to a goods yard/shed and sidings behind the station plus a turntable feeding a loco depot and also a short branch line. It seems as if I'm going to have a lot of spare wire, as I can't take it back now. It seems a bit of a misnomer by Guagemaster to describe it as Layout Wire, if it is not of sufficient capacity.

 

This harks back to good ol' DC.

An analogue controller with lowish current capacity and only powering one or possibly two locos - not a whole DCC system fed with (for example) a 5A controller.

S it is suitable as "layout wire" under DC circumstances.

 

If you've just obtained the reels and they are untouched - see if your supplier will take them back.

 

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3 hours ago, Lichfeldian said:

It seems a bit of a misnomer by Gaugemaster to describe it as Layout Wire, if it is not of sufficient capacity.

 

To be fair to Gaugemaster, 7/0.2 is probably adequate for most modest sized DC layouts that are going to be operated by a DC controller that is only capable of outputting 1 Amp, since a 7/0.2 wire is typically rated at about 1.4 Amps.  As such, it's not really wrong to call it layout wire.

 

However, as has been stated above, it's not really suitable for a DCC power bus, especially not with the system you have purchased.  How thick a wire you need for a DCC power bus depends on the the output of your DCC command station and the size of your layout.  First off, your Sig-na-Track ACE2 is capable of putting out 5 Amps, so your wire needs to be rated to carry at least 5 Amps, although you could use circuit breakers to create separate power districts that then have less power available.

 

But as has been said above, you're also looking for minimal voltage drop along the length of the wire, which means something with a low resistance.  The thicker the wire, the lower the resistance and the less any voltage drop will be.  For a layout of the size you have outlined, I'd say you should be looking at 32/0.2 as a minimum for a DCC power bus.   I can't remember what I eventually purchased for a similar sized layout, but it was something like https://www.ebay.co.uk/itm/50m-Roll-2-5mm-30A-14-AWG-12v-AUTO-CABLE-30-AMP-CAR-WIRING-LOOM-WIRE-AUTOMOTIVE-/251775277191.

 

However, as has been said, you can still use the wire that you have purchased for short dropper wires between the track and the bus (on the basis that resistance is proportional to length and therefore short lengths of thin wire won't have a significant resistance / voltage drop) and you can also use it for other purposes such as platform / street lights and lighting in buildings or wiring up LEDs in a control panel.  Plenty of uses on a layout - just not a DCC power bus.

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10 hours ago, Dungrange said:

 

To be fair to Gaugemaster, 7/0.2 is probably adequate for most modest sized DC layouts that are going to be operated by a DC controller that is only capable of outputting 1 Amp, since a 7/0.2 wire is typically rated at about 1.4 Amps.  As such, it's not really wrong to call it layout wire.

 

I use the UL/CSA  wire ratings in my day job, so reckon they're good enough for train sets., example rating table here:-

 

https://www.hitechcontrols.com/cables/technical-information/58-current-ratings-ul-csa.html

 

Taking 7/0.2 as 24AWG then that does indeed show 1.4A for a multi-conductor cable with 7-24 strands.

 

For a 5A rating the you're looking at  something around 16AWG  for a 7-24 strand cable, maybe go a size up on that as 16AWG is still quite thin for a bus cable IMHO, assuming no great cost increase for 16 to 14  (say) AWG.

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Here we go again many viewpoints to a rather simple question. Most DCC systems output at max 5/8 amps and the wiring should be rated for that. Volt drop should also be a factor but would at most be applicable to a large layout. I myself use mains multi strand single wire. And a certain amount of diversity to power demands should also be allowed for. If the wire has too much resistance short circuits won’t trip the command station or short circuit device which is another by product of under rated wire size. I fully agree with RFS but at no real extra cost as such and the time saved I would go with what I use and it saves all that stripping

Edited by Andymsa
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The only drawback with using domestic wiring is that I want to keep the track buses in red and black colours to match the colours of the original thinner cable, which I will use as droppers. I have therefore bought some red and black 17A car spotlight wiring cable from Halfords, as recommended on a You Tube video I saw recently. Unfortunately it only comes in 4m reels, so is a more expensive option. But then nobody ever said that playing with trains is a cheap hobby!

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17 minutes ago, Lichfeldian said:

The only drawback with using domestic wiring is that I want to keep the track buses in red and black colours to match the colours of the original thinner cable, which I will use as droppers. I have therefore bought some red and black 17A car spotlight wiring cable from Halfords, as recommended on a You Tube video I saw recently. Unfortunately it only comes in 4m reels, so is a more expensive option. But then nobody ever said that playing with trains is a cheap hobby!

 

Plenty of sellers of this type of wire on Ebay, for example this one.

 

Having wrestled with splitting twin-and-earth for my layout a few years ago, I'd probably go down this route next time if I do!

 

The main thing is to ensure it's of adequate size. 

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A good quality silver core cable is the best for power delivery on DCC, as the main track power on such a large layout the thicker the better really.

but whatever you do avoid those scotch block connectors, theyre bloody awful.

Edited by Graham Radish
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I use mains 2.5mm FLEX for the main DCC power bus, rather than 2.5mm T&E cable, since the flex is multi-stranded and is much more flexible than the solid core present in the cable.

 

Here is an example from Screwfix, which is a good price:

 

https://www.screwfix.com/p/nexans-3183y-white-3-core-2-5mm-flexible-cable-10m-coil/7723t

 

The flex has another advantage in that the earth wire is also sheathed, unlike in T&E cable, and can thus be used for other purposes when wiring up your layout. It is also available in a variety of lengths to suit your needs & budget. The only downside of flex is that you have to strip the outer sheathing before use - but this only takes a couple of minutes for a 10m length.

 

I also use 1mm flex for the DCC accessory bus - this is available in a 5-core version with a wider variety of sheathing colours that can help distinguish between different uses under the board.

 

For connections, I use Splice Connectors, which I source from RS Components, to avoid the need to have soldering under the layout. These connectors are available in 2 sizes, one good for the 2.5mm power bus and the smaller one good for the 1.0mm accessory bus. Each connection is a 5 second job with a pair of pliers and is extremely reliable.

 

Yours,  Mike.

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