"Model Train Set" may have caused a fire?

Gary, you said:
"I'd argue that long wiring runs (eg main feed return, connections) should be at least 3A rated wire, or higher regardless of whether youre using DC or DCC"

***Gary, medium hookup wire, the stuff used for droppers, is rated higher than 3 amps - so is most mains fuze wire!!! Its far too small for DCC hookup on all but a 1 metre test track!!

The whole concept of using wire "rated in amps" is fallacious I'm afraid - the issue is voltage drop over distance, and to prevent voltage drop on a wire carrying several amps you need MUCH bigger wire than that.

To keep the wording simple, if the run is more than a few feet, solely to avoid voltage drop under load (for the power bus that the droppers connect to) you should use wire that has the same amount of copper as 240 volt 10 amp wire as a minimum.

For a very large layout, the wire needs to be even bigger... considerably so!

I repeat - all this has nothing to do with current capacity, and everything to do with delivering the same voltage all around the layout when the system is under load.

Richard
DCCconcepts

You said: "Richard - don't blame Gary here , blame me."

***Sincere apologies to Gary and you for the confusion

I'm not an electrician , but the stuff in question comes from Maplins and is described on the packet, as 7/0.2 wire, 16/0.2 wire and 24/0.2 wire, figures of 1.3A , 3A and 5A being quoted on the labels in the shop

The stuff being commonly sold in the UK at shows labelled "layout wire" seems to be the lightest of these 3. If people are using this for main runs of wiring to sections on DC layouts(and I suspect some people are), then I have my doubts about simply hooking a DCC system up to a DC layout

***Sadly, many are - everything from old telecom wire to far too light recycled alarm system wire from skips. We had cause to rewire a club layout recently - I could have knitted with the wire it was so fine - one older member harrumphed at us "no need to rewire it, its fine" and a couple of hours later commented - "why don't the loco's slow down on that far corner anymore" - he wouldn't accept it was the fact that it was the heavier wire reducing the voltage drop of course.....

On my own current small project , I've tried to use 16/0.2 wire for the droppers , though its a little awkward to solder neatly and conceal especially in the thin ballast that results with using SMP. There is a little 7/0.2 wire used where I ran out, and all pieces of track have their own dropper - longer ones have two droppers. Connections from bus to sockets for interboard cable and from NCE facia panel to NCE autoswitch device are 24/0.2 wire

****Actually finer wire is OK for droppers - just keep them less than 300mm long. There's room for compromise on short wires - even fine wire will handle enoug hcurrent, just keep it short! MUCH better to use a wire that you can solder easily and tidily to rail!

Droppers are connected to buses which are taken from 240V mains cable (live and neutral wires) , which is solid core . The layout is 8'6" long, and the system used is NCE PowerCab - the transformer supplied is labelled 1.11A at 15V. I'm being prudent in case something capable of delivering 3A to 4A is ever connected

**** Mains wire is fine for small to medium layouts.

The current club project uses 7/0.2 wire for droppers , wired to power buses made from solid mains cable . The club chairman was talked out of demanding replacement of all dropper wires with 16/0.2 wire on health and safety grounds by someone with a professional electrical background

**** Good - no point in making it harder than it needs to be

I don't think there are any of what you would class as "very large layouts" - the big perminent layouts in 100' x 30' rooms - in existance in the UK - certainly not DCC ones

**** Large layouts to me are over say 40 feet long - but its the length of the bus thats the key - if a 30' long layout has a bus with the booster in the middle of the length, then the run is only 20' really, safe enough with the mains wire "voltage drop wise".

The way I tackle larger layouts is to give each section/baseboard its own "sub bus". These sub busses can be smaller (about 3mm square wire) and they in turn attach via plugs to the main bus, which can be up to 6mm square wire. That way the voltage drop is taken care of and so is the ability to trouble shoot the layout, as its easy to disconnect it a section at a time.

For large layouts I also usually run TWOpower busses - one for all accessory items, one for train power.... that keeps the bus signal clean which gets critical if there's a lot of accessory and computers are also involved....

Actually there are a few very large layouts in UK - but they are very private and seldom see any publicity.

Regareds

Richard
DCCconcepts