DCC bus wire size

"Kevin" wrote

I have not used any sort of bus on my DCC layout, just linked all the track together using standard layout wire.

John.

I used 2.5mm stripped mains cable and ran two wires down all boards and soldered 2 droppers from each piece of rail to each wire. Reason for 2.5mm cable: I had loads in the shed. Reason for 2 droppers: Belt and braces, the layout is for exhibitions.

Martin

Without knowing the scale or size of your railroad empire it's difficult to give an accurate answer. Either John or Martin's answers would do under different circumstances. If it was G scale & out in the garden, even 2.5mm might be too small.

I definitely wouldn't use your 390-555 item as it is just bare tinned copper wire.

You really need to be looking for plastic insulated wire. So if you have an around the walls layout of say 20' by 10' then the 2.5mm csa solution would work well. Look at Screwfix.com for cheap 2.5mm twin and earth cable, say around £24/100m. There may be cheaper stuff available at your local electrical supplies distributor. Strip this and you will get two wires insulated in brown and blue with a third bare. The third may have a thinner csa and might be suitable for some droppers. Any that have to reach across to the bus wires should be insulated. These droppers only need to be around

0.75mm csa or even less. They are only going to be short so the current carrying and volt drop is going to be fine. I would agree with Martin about multiple droppers giving much better current distribution.

Definitely strip the outer sheath from the twin & earth if you go that route, as there are obvious dangers in mixing cables that look like mains cables and aren't, with others that will kill you if you cut into them by mistake. Just cut into the end, grip the centre core with pliers and pull, the centre core will peel through the sheath quicker than it takes to read this.

If using single core cable watch that you don't nick it when stripping the insulation to make your dropper connections. I solder all mine up solid but then terminate each end of the bus at the board ends on screw terminal strips. Then it's plug and sockets from one board to the next. If your boards don't get separated often then these could just be bridging wires into the TB's. Definitely build in some TB's so that you can isolate sections of layout for fault finding. Locating a hidden short needs to be localised.

You can buy single equipment wire, but by the time you price the individual colours you will find that they are just as expensive as the 2.5mm stuff if you don't use the bare earth wire. More expensive if you do.

1.5mm to 2.5mm csa will easily handle the output of a typical DCC booster, say 4-5A. The 2.5mm will give you much better volt-drop performance. So size does matter.

Have a look at Gartner's wiring for DCC site

, but don't get too bogged down with all the detail. Look for the reasons why bigger is best....

Regards

Len

Depends on the size and complexity of your layout. Mine is ~2m * 1m, with 2 loops and goods yard, OO Gauge. I've used 2 core mains cable rated at 5amps going from the controller to a distribution board underneath the main board. Then I have 2 spurs going off to the main tracks, and a few spurs going to the goods yard. Never had a problem with getting juice to the track, except dirty wheels/track (and a dodgy point)

I run 2 trains on the loops, and may well have one working in the goods yard, but that's about the most I'll ever do. I did have all 7 loco's running at once, just to see if I blew anything up, but the only problem I had was the almighty crash that followed.

HTH,

Ian

I used 4mm Red and Black singles run around the layout which is a rough square of about 40ft circumference. With a wider main board than the other three.

The wires run about 20ft in both directions from a central point approximately at the middle of the main board and are terminated at each end with a 100 ohm resistor and 40 uF capacitor. From this I have soldered 2.5mm Red and Black singles about every metre which each terminate in a large chocolate block. I have then soldered 12" long 24/0.2mm Red and Black droppers to each pair of fishplates, these are then connected in bunches to the nearest chocolate block. Every fishplate is wired.

Reason for using the wire that I have, I had plenty at home, and the heavier gauge wire, the better, bit of a bugger soldering the 2.5mm to the 4mm though.

Overkill, very, very possibly, but after my first debacle of soldering all the track to the fishplates and droppers to the track, not allowing for any possible expansion I have made a point of not soldering the track to the fishplates, and have left a 0.5mm gap between every joint, by my soldering droppers from every fishplate, I hope to ensure excellant electrical conductivity at all areas of the track.

The only place I will need to solder droppers directly to the track will be on one leg of my wye as the fishplates at each end of this leg are insulated in order to prevent shorting and allow the use of a Lenz reversing module (not yet fitted).

Eddie.

Kevin,

I use 7 amp mains cable with copper bell wire droppers from every rail. Droppers from every rail is good practice anyway and in my case, my layout was using this in pre-DCC days - it means that you don't rely on fishplates to carry current. Fishplates can fail if you paint your track and if, like me, you have a large layout, you will get a voltage drop over long distances. I use 7 amp mains cable as 'belt and braces'. The Lenz 100 is cable of putting out 5 amps, so anyone using cable which is not rated at 5 amps is taking a real risk if they have lots of locos on a layout (remember that each loco can draw about .5 amps). The practice should be the same as main electricity: the cabling should be rated higher than the expected highest current. I don't personally believe that ordinary layout wire is sufficient for DCC because it cannot carry higher currents. This is one of my 'beefs': too many people use underated wire for their layouts and wonder why a Peco point motor (which can momentarily draw more than 2A) doesn't work on the end of 20m of 250ma wire!

Graham Plowman

In message , snipped-for-privacy@gppsoftware.com writes

I agree with Graham, except that for my garden railway, with its much longer runs, I use cable which can carry at least 13 amps, and some of it is ring main cable which can carry 40 amps.

Maximum number of locos operating at one time x 1/2amp each --> minimum current capacity needed. Double that, and use a bus wire that will handle at least that amperage.

HTH

Thanks Jane.

In actual fact, people shouldn't be deciding on cable based on its physical measurements. They should be choosing it based on its amperage rating.

Graham Plowman

Jane Sullivan wrote:

Graham,

If you're referring to people quoting the CSA of cables, then the current carrying capacity is directly proportional to the cross sectional area of a cable and is a valid reference for choosing cable. IIRC, 2.5mm copper is rated for 15A, 1.5mm is rated for 10A and 1mm is rated for 5A, but someone might confirm in case my brain has given up :-)

Just found this on the web for copper wire - a bit higher than my figures, but mine are probably derated for domestic use.

core size current (A)*see note mm2

1.0 14 1.5 18 2.5 24 4.0 32 6.0 40 10 53

• The currents and wattages shown are for the cables in 'free air' installations, the cables should be derated if cables are run together or in such a way that the thermal rise of the cable is not free to dissipate.

Jim.

In message , Jim Guthrie writes

Is this for single wire cable, or for multiple wire flex?

Jane,

Good question :-) The way I read the web page which I got the details from was that it meant single conductor cable. Multiple strand cable was usually quoted with the number of strands and the individual wire gauge - i.e.7/029, 7/036, etc - and there was no mention of anything like that on that site.

I think that stranded cable in the sizes normally used in domestic wiring became obsolete many years ago. I do remember my father, who was an electrician, cursing the advent of solid cable since it was so easy to nip and break single copper at a junction box, which could mean re-running another piece of cable to replace it.

Jim.

Jim Guthrie wrote: [...]

?????

I don't understand this comment. Are you referring to a T-splice? I thought T-splices were outlawed for power cabling.

In message , Jim Guthrie writes

And if you use it for model railway wiring you have to be careful that you don't bend it and re-bend it at the same place, because that will weaken it and it will break.

Incidentally, I hate so-called "bell wire" for the same reason, and would rather run a pair of 7/002 stranded wires instead.

Hi Jane,

The figures quoted by Jim would appear to be for single cables and are maximum wattages, 2.5mm sq CSA twin and earth (15 amp) is usually used for house lighting circuits in conjunction with a 5amp fuse.

4mm sq CSA twin and earth (30 amp) is usually used for domestic ring mains with a 15 amp fuse. 6mm Sq CSA twin and earth (35 amp) is usually used for electric cooker installations and low kilowattage shower installation. 10mm Sq CSA (45 amp) should be used for shower installations of 9.5kw or higher and even 9kw if the cable run is longer than about 15ft.

Larger the cable the lower the internal resistance and therefore the voltage drop, downside to this is you need a heavy soldering iron to solder 2.5mm to

4mm as the heat dissipates rapidly along all that copper wire.

The longer the length of cable required the more important it is to use thicker cable to help counteract the voltage drop.

Eddie.

Hi Wolf,

Not in the UK, we still use stranded wire is sizes up to and including 4mm Sq CSA. But have recently changed our colour coding from Red and Black, to Brown and Blue. So large amounts of Red/Black Singles and Twin/Earth available cheap.

Eddie.

I've just realised my my calculations are up the swanny using cross sectional area=pie x Diameter which is of course the formula for the circumference. I should have use pie x diameter squared / 4.

Kevin

Wolf,

A lot of the connections in UK domestic electrical equipment use a brass screw which clamps the wire in a hole in the terminal. With single copper cable it is easy to over tighten the screw and nick the copper wire sufficient for it to break under the screw then drop out of the terminal. If you've laid your wire neatly, especially in conduits, then you often have to do a re-run of the cable since the broken cable is too short. With the earlier stranded cable, this rarely happened.

Jim.

AFAIK the rating is per conductor. If you have a 15 amp circuit, you need 2x2.5 sq mm wires - live and neutral return - plus an earth.

Even worse was the aluminium wiring used in Canada in the early 1970s. It wasn't long before it was outlawed. A house I bought new in 1972 had it, and I discovered a junction box with the neutral and ground wired together, because there was a break in the neutral somewhere else.