Wiring capacity

Chris Mitton
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Joined: Sun Aug 31, 2008 1:18 pm

Wiring capacity

Postby Chris Mitton » Wed Aug 18, 2010 12:15 am

Hi all

As a novice in P4, I'm just about to start wiring up the first of my baseboards. Before I go too far, I'd appreciate advice from those who've "been there, done that" on what size of wire to use. It strikes me that, with DCC, a single section of track could be carrying enough current to drive three or even more locos at once, and some of the wiring I've seen looks a bit flimsy to me to carry that load - or am I being overcautious?

I've got a reasonable supply (in multi colours) of two kinds of wire - one is single-stranded, 0.58 mm diameter, the other has 16 strands 0.2 mm diameter - that I envisage using (one or the other) for under-board wiring. I've also got some cable (designed for SCART leads) that I could use for joining boards to control panel, connected via 25-pin D-shaped plugs/sockets (actually computer RS232 connectors). Each wire in this appears to have 7 strands, about 0.10 mm diam. I don't know much about RF transmission, but I suspect the currents carried in these cables (on their home ground) are minute - the circuits only worry about whether they're there or not, they don't deliver any significant power. Am I right? Is this cable man enough?

My A level physics (from nearly half a century ago!) tells me that if 1 mm2 twin/earth can carry 5 amps (a normal house lighting circuit), then the 16-strand ought to be comfortable with about half that, but it's a pig to solder into the plugs in a confined space - whereas the single-strand is much easier but has only about half its cross-section and so shouldn't really carry much more than 1 amp. Is this enough? On the other hand, I don't really want to have half the National Grid draped across my loft.....

Any advice appreciated....
Regards
Chris

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John Bateson
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Joined: Wed Jul 02, 2008 6:39 pm

Re: Wiring capacity

Postby John Bateson » Wed Aug 18, 2010 8:28 am

Chris,
Some thoughts :-
16/02 cable is rated at 6A normally. This is usually more than enough to drive a 4mm train even with full carriage lighting.
Where this may fall short is when using DCC you have multiple parallel circuits and drive several trains and maybe a few accessory decoders.
Where this may also fall short is when you wrap such cables in a loom - the heating effect will reduce the current rating by almost half.
Long lengths (over 30ft) will also cause voltage drops commensurate with the current being delivered. This would be a problem only for larger layouts or the Test Track (TT2) from DRAG - I would like to see some measurements from them ...
I use 16/02 cable for all track feeds. I don't use parallel feeds to other circuits.
7/02 wire is rated at 1.4A normally. If the layout is small then it will be suitable for most 4mm trains - but the same caveats apply as for the 16/02 cabling - only more so.
I use 7/02 wire only for accessories such as point motors

16/02 wire will solder into the bucket slots on a normal 'D' type connector with ease. I also use heat shrink sleeving.

Single strand wire is a real No-No for the model railway. Bend it too many times and the stress fractures at the bend points not only reduce current capacity, but will cause a break just when you don't want it. I managed to offend a modeller many years ago after he had stripped an old Post Office of its relays and wiring by declining his otherwise very kind offer of a ton of single strand cable!

Avoid SCART cables and other associated offerings for driving trains and interboard connections - they just do not have the current capacity - and being usually in sleeving this is reduced anyway.

There will be other views expressed here anyway ....
John
Slaving away still on GCR stuff ...

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grovenor-2685
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Re: Wiring capacity

Postby grovenor-2685 » Wed Aug 18, 2010 10:59 am

Chris,
Before confirming or otherwise how you can best use the wire you have I think a bit more information about your layout would be useful.
So far you have said DCC and in the loft and that you envisage having control panels that you would want to unplug.
So questions.
1. How big is it, in particular what will be the distance from the DCC Command Station to the furthest section of track?
2. Are you building fixed boards, dismountable boards that can be taken out to work on, or portable boards that may be taken to exhibitions?
3. Do you envisage any need for signalling using track circuits that would need the rails sectionalising?
4. How do you intend operating points? (Manual, solenoids, tortoise, servos etc. and how far from the control panel will the points be?
5. How many locos do you envisage having on the layout, a, running simultaneously, b, standing around on shed, in fiddle yard etc.
6. Any other electrical accessories? eg Uncoupling magnets, signals,

Unless your layout is very big I don't see any reason not to use the wire you have but the above answers will guide suggestions as to how best to use it.
Regards
Regards
Keith
Grovenor Sidings

craig_whilding

Re: Wiring capacity

Postby craig_whilding » Wed Aug 18, 2010 11:31 am

I'd suggest you look into DCC track bus wiring on the web.

For the Manchester layout the droppers i've done so far on the rebuild are 16/0.2 onto a 13amp mains solid copper bus running parallel to the track under the boards. Its a double track with a separate pair of bus bars for each to allow separate circuit breakers on each circuit if someone trips one. We do have some complex pointwork going in though I need to work out the correct arrangement to avoid cutting out both tracks if we have an issue..

I'd try to minimise the amount of ways connectors you use if you don't need all the pins, interboard connectors and the flex to them always seems harder than the wiring under each board.

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Tim V
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Re: Wiring capacity

Postby Tim V » Wed Aug 18, 2010 6:18 pm

A small point, but DCC needs very few cross joint connections. The minimum is two after all! You would hardly need the 21 connectors in a scart socket.

Having said that, I normally run three across any joint, one rail, one control bus and one common return.
Tim V
(Not all railways in Somerset went to Dorset)


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