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12v analogue - track feed wire queries


john new

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I've used search but the answers I found in earlier posts were confusing as not written for non-electricians so hoping someone can summarise current thinking:-

 

1) Standard 12V analogue track feed wire - Medium weight or thin weight wire?

 

On my last Hornby Dublo exhibition layout I used very thin wire both single strand and multi-strand. (Split out from old PC network cabling) That seemed to work OK despite the amperage load drawn by the old HD locos but was a bit flimsy and therefore prone to physical damage in transit. However I believe thicker wire is also recommended from an electrical perspective, of a thickness similar to the type of cable used for powering low amperage mains kit. Is it true that medium weight flex wire is recommended or will either type do? I ask as I have a good stock of multi-coloured wire of either type I can use.

 

2) Avoid using stripped out mains wire for low voltage supply due to potential confusion of high & low voltage feeds.

 

Fully appreciate that modern advice from a safety point of view. I've done that in the past but now I've read of this issue with PAT Regs I actually concur with the advice. However going back to (1) does that mean that if split down the thicker multi-core flex cable I have in stock into the individual coloured wires I can't use the plain red, black, green, brown and blue as they are/have been the colours used in mains cabling?

 

Sorry if these read as numpty questions and thanks in advance for any advice offered.

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There's nothing stopping you using stripped out mains cable for layout wiring, indeed it's generally a good cost vs. rating compromise. The PAT issue only affects mains controllers. I certainly wouldn't want mains voltages under the baseboards but that's very different to using mains cable.

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1) Standard 12V analogue track feed wire - Medium weight or thin weight wire?

I would not use single strand wire for a portable layout as it's more prone to damage. Apart from that, wire is wire and the golden rules are:

The higher the current, the larger diameter wire is needed.

The longer the individual wire, the larger the diameter needs to be for a given maximum voltage drop at aparticular current.

 

For a DC layout I assume you have section switches and each circuit is powering only one loco (or maybe double heading) plus maybe carriage lighting. The wire needs to be an appropriate size for the largest single load.

 

2) Avoid using stripped out mains wire for low voltage supply due to potential confusion of high & low voltage feeds.

 

That's mostly nonsense, otherwise you couldn't use any of the colours used for mains for anything else. Don't use stripped out wire of unknown provenance. Buying new and stripping it is fine.

 

Mains should not be wired around the layout to any great extent and prefereably not at all. If it is, it MUST use appropriate cabling, and connectors, with the outer sheath intact that clearly looks like a mains cable, or be innaccessible. NEVER, NEVER, NEVER wire mains around a layout using single cores.

 

With that rule applied, any colour wire can be used for the low voltage wiring.

 

Andrew Crosland

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Ah, but the comments about cable colours are why I got confused earlier and posted these two questions as it conflicts with

 

IIRC, using standard mains, (low voltage) coloured cable for ultra low voltage runs is theoretically against 16th Ed. rules and a PAT test failure

 

which I found/read on here earlier this afternoon in topic thread http://www.rmweb.co.uk/community/index.php?/topic/20358-240-v-mains-cable /

 

The layout I'm building may never be good enough to get near to the NEC or other exhibition venues where panels etc get properly inspected but if an issue can be designed out right at the start that is the time to do it.

 

Was that comment about what are actually now (IIRC) the 17th edition wiring regs wrong or does it only apply to the link between a mains power transformer box and the control panel?

 

I know if I ever was to take the old HD layout out on the circuit again (it is mothballed not dismantled) it will need a either new control panel box (wooden transformer housing) or the transformers moving to a new high-voltage box that meets current standards. I'm just trying to avoid repeating any other old tricks which were OK back in the '90s but are no longer acceptable.

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I really don't think PAT testing applies to layouts, it applies to mains controllers, unless there is an EU directive somewhere that classifies a model railway layout as an appliance, in which case passing EMC testing could get interesting. I suppose a layout built for commercial sale with an integrated mains controller might be a different issue, but even that's pretty far fetched.

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Was that comment about what are actually now (IIRC) the 17th edition wiring regs wrong or does it only apply to the link between a mains power transformer box and the control panel?

 

 

I'm not an electrician but I'm fairly sure the IEE wiring reg. apply to fixed installations only, i.e buildings, in which case I'm 100% sure a toy train set is not within scope.

 

PAT testing, which is intended to ensure safety in the workplace requires visual inspection of external cabling in accordance with the IEE code of practice, which is not the same as the previously mentioned wiring regs.

 

Google provided this rather useful summary of a PAT testing policy:-

 

http://www.coventry-catholicdeanery.org.uk/Pat%20Testing/PAT%20Test%20Policy%20Approval%20Document.pdf

 

If under baseboard wiring is considered within scope then that should provide a good few hours 'entertainment' for the PAT tester per layout!

 

 

EDIT: if internal wiring was part of PAT testing then every desktop PC in the land would fail, as they all use red/black/brown/blue wiring for different low voltage power supplies.

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Hi

 

I find that for normal track feeds (12V dc) and turnout motor feeds (16V ac) that either 10/0.1 or 16/0.2 is more than sufficient for most applications. It is fairly flexible. I tend to use the heavier cable for common returns. Both are available in a number of colours to aid latter fault finding.

 

HTH.

 

SS

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The comment about wire colours slightly surprised me but I can see several circumstances where it would have relevance. I didn't know the definitive answer that is why I asked the question based on the earlier thread. The comparison with the PC internals is probably definitive. I guess the issue, if there actually is one, is low voltage connections from a mains power box up to the panel, especially on the internals of the power box.

 

My practical experience with the SLS display stand over the last few years, including at the NEC, is that none of the individual 240V items I plugged in on my side of the RCD were individually tested but the RCD was. Nothing was allowed to be connected to the live line before the test was carried out.

 

Conversely a mains fed layout, at least as far as the transformer and perhaps beyond that, is a Portable Appliance so logically should be subject to test just like any other independent mains device. My guess is pragmatism has broken out at exhibitions, hence only testing the RCD, and then insisting the safety protection is routing all mains feeds via that.

 

Regarding wire -

 

I find that for normal track feeds (12V dc) and turnout motor feeds (16V ac) that either 10/0.1 or 16/0.2 is more than sufficient for most applications.

 

(Edit - replacement section) I've found the key to that reply now on the Maplins web-site (Number of strands/cable thickness in mm)

 

So am I correctly interpreting that response as (in lay terms) use flex not single strand and thin will do? Use slightly thicker for common return.

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Some organisations do seem to interpret PAT testing as beginning and ending with plugging the appliance to a PAT tester and pressing a button, whereas in reality the visual inspection element is an integral part of PAT testing. I agree a pragamatic approach is needed in reality, particularly as PAT testing is being applied in areas where the legislation never intended it to be used, like model railway exhibitions.

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Some organisations do seem to interpret PAT testing as beginning and ending with plugging the appliance to a PAT tester and pressing a button, whereas in reality the visual inspection element is an integral part of PAT testing. I agree a pragamatic approach is needed in reality, particularly as PAT testing is being applied in areas where the legislation never intended it to be used, like model railway exhibitions.

Electrical safety applies everywhere, not just in the workplace, so it definitely applies to public exhibition venues.

 

How you demonstrate safety is the contentious issue. Portable Appliance Testing PAT is not the be all and end all of demonstrating electrical safety. In many cases a simple periodic visual inspection is safficient. Indiscriminate use of test equipment can actually damage the equipment being tested.

 

Wire colours used on a layout cannot cause a PAT failure as the layout itself is totally outside the scope of PAT if it has no mains on it (which it shouldn't have).

 

Andrew Crosland

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Electrical safety applies everywhere, not just in the workplace, so it definitely applies to public exhibition venues.

Andrew Crosland

 

In practise yes, but PAT testing was a specific addition to health and safety at work legislation, so is worded in that context.

 

 

How you demonstrate safety is the contentious issue. Portable Appliance Testing PAT is not the be all and end all of demonstrating electrical safety. In many cases a simple periodic visual inspection is safficient. Indiscriminate use of test equipment can actually damage the equipment being tested.

 

Wire colours used on a layout cannot cause a PAT failure as the layout itself is totally outside the scope of PAT if it has no mains on it (which it shouldn't have).

 

Andrew Crosland

 

Agreed, the primary requirement of the legislation is to ensure equipment is safe, PAT testing is just the recommended/required means of doing that.

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Some organisations do seem to interpret PAT testing as beginning and ending with plugging the appliance to a PAT tester and pressing a button, whereas in reality the visual inspection element is an integral part of PAT testing. I agree a pragamatic approach is needed in reality, particularly as PAT testing is being applied in areas where the legislation never intended it to be used, like model railway exhibitions.

 

Indeed, the visual testing ought to be the first thing done. If the mains cord is badly nicked or a broken plug or some other fault. then it has already failed & plugging the device into a PAT tester, is a waste of time.

 

Why should model railway exhibitions be exempt? If such a layout is wired up in a dangerous manner, then it ought not be plugged in anywhere in a public place, or indeed in a private home.

 

 

Kevin Martin

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When wiring any layout these days I would always approach it from the point of view that good wiring practice should apply to DC and DCC layouts.

 

That means I would adopt the approach of a bus bar for the main circuit and would use mains cable (typically the twin core for lighting) around the boards. I would then take multiple local droppers off to the track using multistrand layout wiring cable. Everything colour coded for ease of following and testing.

 

I would keep all mains well away from the board. It shouldn't be needed, it is safer that way and should keep the exhibition managers happy. Keep the mains transformers in a suitable box on the floor and have only low voltage cables climbing up layout legs.

 

I wouldn't use stripped out computer cables or flat cables they are just to fragile.

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Thanks for the feedback all.

 

Wire thickness - As you read in my original post I was unlikely to be repeating the use of the very thin wires from the recycled network cabling (as I had found they weren't physically durable enough), my query was more about seeing if there was a consensus about how much heavier a weight of wire I should upgrade to. Medium weight seems fine and I still have some in-hand from earlier projects/layouts so will use that.

 

Regarding colours - consensus would appear that the advice given in the earlier thread about blue/brown etc was overkill, although common sense dictates it would apply where the mains and low voltage circuits could actually be misinterpreted. (For example the in/out circuits within a transformer box)

 

Low voltage only at the layout - I would have done this anyway for any new build but consensus also that modern practice is to have the mains transformer box separated from the control panel with only a low voltage umbilical supply between them. (My HD layout had the transformers in a single control panel box)

 

I have, usefully, picked up from this one aspect I might not have thought to change from past practice namely that lighting to be 12v halogen or 12v caravan lighting, not directly mains fed, so there will be no mains power at the layout other than the one lead into the controller. As that is sealed, no wiring colour clash possible.

 

Fortunately this is only a small layout and as I have a suitable Gaugemaster sealed unit controller/transformer I don't have to build a new mains power box for separate transformers just yet. Thanks to the above advice hopefully I can get the basic layout wiring in later today.

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Hi John.

What Kenton has said above is spot on.Use common sense. Do it right the first time & you won't need to do it again.

Use color coding & label your wires.That way if you look at a wire you will know exactly whats in it & where its going.

Use the proper wire for the job & don't use scrap wire or wire you have left over from an old computer or phone system.

Don't confuse your self with wiring regulations & pat testing unless you are doing the work commercially or are doing it for a business.

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Siberian snooper wrote -

 

I find that for normal track feeds (12V dc) and turnout motor feeds (16V ac) that either 10/0.1 or 16/0.2 is more than sufficient for most applications. It is fairly flexible

 

Out of curiosity as I was digging out my stocks I compared that recommendation with the thin flex I used for wiring within the boards on the old Hornby Dublo layout. The Maplin spec' for 10/0.1 is 0.1mm copper, 0.3mm PVC sheath, approx 0.9mm overall dia. Putting the digital calipers on what I had used gives 7/0.1mm copper, sheath thickness??, overall dia 0.75mm.

 

Thinner yes, but not that much so.

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Out of curiosity as I was digging out my stocks I compared that recommendation with the thin flex I used for wiring within the boards on the old Hornby Dublo layout. The Maplin spec' for 10/0.1 is 0.1mm copper, 0.3mm PVC sheath, approx 0.9mm overall dia. Putting the digital calipers on what I had used gives 7/0.1mm copper, sheath thickness??, overall dia 0.75mm.

 

Thinner yes, but not that much so.

Only 0.15mm difference in overall diameter but going from 7/0.1 to 10/0.1 is almot 50% increase in copper area and corresponding current handling capability.

 

With such thin wire you need to be extra careful when stripping, to ensure you don't break a strand or two.

 

I would use 16/0.2 as a minimum.

 

Andrew Crosland

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I wasn't planning to use the 7/0.1 flex again; more surprised that the difference to the recommendation was as small as it was!

 

I have about 3metres of 12 core of heavier gauge left in stock. Trying to work out the colours and wiring plot currently to use as few connections to/from the control panel as possible.

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Out of curiosity as I was digging out my stocks I compared that recommendation with the thin flex I used for wiring within the boards on the old Hornby Dublo layout. The Maplin spec' for 10/0.1 is 0.1mm copper, 0.3mm PVC sheath, approx 0.9mm overall dia. Putting the digital calipers on what I had used gives 7/0.1mm copper, sheath thickness??, overall dia 0.75mm.

 

Thinner yes, but not that much so.

 

I would use 16/0.2 as well but only if 300mm/1ft or less in length.Anything longer than that I would go to 24/0.2 or cut the 16/0.2 about 6" below the baseboard & join up with 32/0.2 or 24/0.2 from there to the main bus wires.I use all stranded wire.

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Back to PAT testing....Firstly I am not a qualified electrician or electrical engineer, but I did study electronics and electrical engineering at college.

As I understand it the process should involve a physical inspection of an appliance. The PAT tester however is designed to check an Appliance and it's power leads are not shorting to earth in other words it checks the health of the insulation on cables and that the device is not internally allowing electrical current to flow to earth either.

The thing is in a layout most of the leads are actually hidden and should be neatly fastened to the underside of the layout, certainly in the case of exhibition layouts. the irony of the PAT test is that part of it's job is to protect the operators from live external metal, in our case we need bare conductor, in fact most of the load carrying circuitry on display is actually bare metal.

Finally there is one other thing to bear in mind. If a device was to have a short circuit a fuse would go. Wouldn't it? Not necessarily, the fuse is to protect the device from damage. It is not there to protect the user of the device (although it generally does). However a circumstance could allow a small amount of current to earth via the case of a device and not blow a fuse. The device would be working fine and yet still have a electrically live case. Generally 0.06 Amps is enough to kill and your device may have a 1 amp fuse. This is why we use a RCD outside. These devices can detect a difference in current between Live and Neutral (the current flow through live and neutral between the plug and the device should be the same) and if there is a difference the breaker stops the electrical supply.

 

In conclusion If I was a PAT tester I would test a layout but I would be sensible about it, more importantly I would make sure I knew exactly what I was testing and how to do it before the day.

 

Cheers

Colin

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Electrical safety applies everywhere, not just in the workplace, so it definitely applies to public exhibition venues.

 

How you demonstrate safety is the contentious issue. Portable Appliance Testing PAT is not the be all and end all of demonstrating electrical safety. In many cases a simple periodic visual inspection is safficient. Indiscriminate use of test equipment can actually damage the equipment being tested.

 

Wire colours used on a layout cannot cause a PAT failure as the layout itself is totally outside the scope of PAT if it has no mains on it (which it shouldn't have).

 

Andrew Crosland

 

A professional tester told me about a school full of equipment he was testing properly. When he went back for the 3rd day to do the next batch of equipment for testing, he was quietly taken aside and asked why it was taking so long to do. It transpired that the previous person, had merely replaced the labels without doing any tests at all.

 

He also claims that in his experience that about 2% of computer IEC type cords have the active & neutral reversed.

 

Kevin Martin

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Back to PAT testing....Firstly I am not a qualified electrician or electrical engineer, but I did study electronics and electrical engineering at college. As I understand it the process should involve a physical inspection of an appliance. The PAT tester however is designed to check an Appliance and it's power leads are not shorting to earth in other words it checks the health of the insulation on cables and that the device is not internally allowing electrical current to flow to earth either.

The thing is in a layout most of the leads are actually hidden and should be neatly fastened to the underside of the layout, certainly in the case of exhibition layouts. the irony of the PAT test is that part of it's job is to protect the operators from live external metal, in our case we need bare conductor, in fact most of the load carrying circuitry on display is actually bare metal.

 

Finally there is one other thing to bear in mind. If a device was to have a short circuit a fuse would go. Wouldn't it? Not necessarily, the fuse is to protect the device from damage. It is not there to protect the user of the device (although it generally does). However a circumstance could allow a small amount of current to earth via the case of a device and not blow a fuse. The device would be working fine and yet still have a electrically live case. Generally 0.06 Amps is enough to kill and your device may have a 1 amp fuse. This is why we use a RCD outside. These devices can detect a difference in current between Live and Neutral (the current flow through live and neutral between the plug and the device should be the same) and if there is a difference the breaker stops the electrical supply.

 

In conclusion If I was a PAT tester I would test a layout but I would be sensible about it, more importantly I would make sure I knew exactly what I was testing and how to do it before the day.

 

Cheers

Colin

 

 

As someone who does do a small amount of "Test & Tag" as it is called in Australia, you are correct in that it is a multipart test. First is a visual test, where you look for damaged cords and faulty (broken cord retainers usually) plugs & sockets, also checking to make sure that casings, covers or guards etc are complete. Or sub-standard materials, not long ago, I rejected an old rubber insulated extension lead - illegal here for 30 odd years). If any item fails these 'tests' then it has already failed and you don't even bother testing any further.

 

So far, railway modellers (everyone really) ought to be quite capable of doing the above tests, before they even think of getting some one to test it for them, it is our old (but now deceased?) friend "Common Sense".

 

 

 

Only then do you get out the PAT tester (or as I do, the multimeter & megger as I don't do enough to justify a PAT) and check the earth to case as being <2 ohms (if not double insulated), the polarity of cords (including the colour scheme - we use the same colours as Britain, even though plugs & sockets are different). Next you short out the active & neutral on the plug and connect one side to the megger & the other side to the earth pin & press the button for high voltage >500 volts and you ought to get >2 Meg resistance.

 

Of course we are only talking about mains stuff here, that has to be right, but the low voltage side from the transformers etc, can be to almost any standard as long as it is seperated from the mains, or doesn't use sheathed mains cable for low voltage applications.

 

I see no reason why a layout shouldn't be tested as it is just a large appliance. Of course if the layout mains wiring is really sub-standard, ask the owner if they really want it tested, because you aren't going to pass it, as your name will be on it. I did this to a club member who submitted a couple of dodgy power supplies in a batch of 10 or so for testing, I picked out the two and returned & tested the rest, which passed. Of the 2 he fitted a new cord to one, the other I never saw again.

 

 

You are also correct in that it should be done in advance, I couldn't imagine anything worse than having to tell the owner(s) that their exhibit can't be plugged in just before the exhibition doors are due to open. Increasingly, public venues simply WILL NOT allow untested equipment into their buildings.

 

 

Kevin Martin

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The thing is in a layout most of the leads are actually hidden and should be neatly fastened to the underside of the layout, certainly in the case of [/size]exhibition layouts. the irony of the PAT test is that part of it's job is to protect the operators from live external metal, in our case we need bare conductor, in fact most of the load carrying circuitry on display is actually bare metal.

 

Well I would argue that mains wires shoyuld NOT be hidden and neatly fastebed to the underside of the layout. They should be completely detachable and accessible for easy testing.

 

Anything on the layout side of the transformers is outside the scope of "PAT testing" as most people understand the term. Anyone trying to do a high voltage insulation test on my layout wiring would get the test probes stuck where the sun doesn't shine :angry:

 

Andrew Crosland

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I see no reason why a layout shouldn't be tested as it is just a large appliance.

 

Kevin Martin

I disagree that the entire layout is an appliance, for sure the mains controller is, but that's it - unless folk have are routing mains supplies within their baseboards, which is never a good idea IMHO.

 

Well I would argue that mains wires shoyuld NOT be hidden and neatly fastebed to the underside of the layout. They should be completely detachable and accessible for easy testing.

 

Anything on the layout side of the transformers is outside the scope of "PAT testing" as most people understand the term. Anyone trying to do a high voltage insulation test on my layout wiring would get the test probes stuck where the sun doesn't shine :angry:

 

Andrew Crosland

Like he said.

 

 

EDIT:

Without wishing to 'cross thread' with the current H&S thread over in W&S then I wonder how many people in total have attended model railway exhibitions over the last 50 years (that number must be in millions), and how many electrocutions have occurred in that time?

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Safety attitudes have changed over time and perhaps, "but for the grace of God" applies.

 

1) Back in the 70s I had a mobile disco. Looking back now the less said about part of the the wiring loom I lashed up on the lighting rig for that the better. Shielded yes, fortunately beer didn't get spilt over/into it, perforated hardboard backing to keep weight down/what I had to hand and chocolate box jointing, not covered junction boxes! EDIT (Add) - probably soldered wires wrapped with insulating tape too.

 

2) I'm not saying who's layout it was (not mine I rapidly add) but many years ago when I was helping modeller X for the weekend he DID take a home made/home wired mains power joining lead to a show accidentally wired with the standard male 13A mains plug on both ends! Also back in those days (late 70s or early 80s) it was the norm' to build the panels and mains lighting feeds integral, this cable plug joint WAS between two baseboards at layout level Tiredness can creep in finishing off those last bits on a new layout, luckily we found it, swapped the rogue plug/socket round during set up and before plugging anything in!

 

3) Mentioned above, in the 1990s I had my HD Classic Train Set layout touring. Yes I built a new control panel as the old rubber insulation on the original Meccano gear was past it. However even that recently in time terms varnished, all wood panels were seen as acceptable. I built mine just like the one's we were building for the club layouts. The shielding I built into it was thought out, with the lid open the mains terminals are covered etc., however it could have been vulnerable to coffee spils etc. If I was using it again the two mains transformers would need to be removed to a floor box which was waterproof etc.

 

I mention these only because they seemed Ok at the time, and some were before we even thought about RCDs for circuitry protection.

 

Because from a modern perspective I know I've done it wrongly myself/seen it done wrongly by others I have looked for answers and asked questions on the contemporary thinking.

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