What size wire to use?

[Dieselbob]

Hi Chris

Be careful when asking about wires to Railway modellers, most of then find there cables in skips and by rumaging through the garden shed, and they end up with cables that they have no idea of its size or current rating.

My advise to you as an electrician, you have a small layout with a powercab and 3 amp booster, go to an electrical wholesaler and buy 50 metres of 1.0 mm Twin & Earth cable, its a solid draw cable and perfect for your needs (about £16.00 + vat).

Strip the bare earth out, and remove the outer insulation, you need to put some twists in the cables aprox every 6 inches (because it is carrying data), tap off the 1.00 mm cables where ever you want to put your droppers, use the same cable as droppers as a solid cable can be stripped easily and fed up through the baseboard, when above the baseboard you can put a nice bend into the cable and form it into the web of your track and solder neater than with flex.

Do not get too carried away with how much current a certain cable can carry, 1.00 mm solid cable can generally take 12-14 amps depending on whose chart you look at, cable current ratings can change dramatically depending on there locations.

Should you upgrade to a 5amp Power-Pro in the future you will still be well in.

Cheers

Bob

(www.buztech.com)

[Alan Kettlewell]

Hi Chris

Obviously your not visiting the right web site.

Link to my DCC page Wire sizes are discussed here.

 

My rule of thumb is... For the actual DCC bus always use the largest size of conductor (wire gauge) thats practicable.

 

As for dropper wires, if every section of track is fitted with droppers then 16/0.2mm will be fine. Do try to keep the length of dropper between rail and bus wire as short as possible.

 

Your Gaugemaster 'layout wire' which is 7/0.2mm is too small to use for DCC especially with "O" gauge current demands. Use it for feeding non DCC items like colour light signalling, LED indications back to the mimic panel and feeds to any Stall style point motors (not solenoid ones though).

 

Brian,

 

I had a visit to your website and read your very well put together info on layout wiring - thank you it is very useful indeed. Reading this thread has been encouraging as I'm a solo modeller and everything I do on the layout is either from common sense, search and discovery (on forums such as this), basic intuition or plain old luck. Of course I get things wrong from time to time but I'm happy to confirm that overall my wiring methods, by and large, follow the standards discussed here and on your website Brian.

 

One thing that I did glean from your website is a tip about insulating points. I use Peco insulating points on my layout, about 100 of them - because these are what I bought some time ago together with hundreds of yards of code 100 flexitrack. Not the best of decisions but I'm not about to tear it all up and replace it all so I make do with it.

 

By and large my layout runs fairly well, considering I've taken no particular steps with additional wiring of points, no polarity change switches fitted anywhere - I guess I'm just lucky. It's a fairly large layout; 10m x 3m using all Lenz DCC equipment and automated with RR&Co Train Controller.

 

However, I do suffer from the occasional problem due to wheel sets shorting on the points and at those times really wish I'd have chosen electrofrog - isn't hindsight wonderful! So I was reading your tips for points that are already laid about resolving this problem with a little effort, a cutting disk and an extra feed or two in the right places. I'll be trying this out very soon and look forward to improved running. I hadn't thought of this and it seems such a simple fix. So a big thank you for your time and effort to bring such useful information to our forum. What would we do without it?

 

Regards

Alan

[Phil S]

The "maximum current which can be SUSTAINED WITHOUT TRIPPING" is just the normal operating limit of the booster.

 

A "short circuit" is a fault and should *always* cause the booster or controller to trip.

 

Andrew Crosland

 

Phil: The 'maximum current which can be sustained without tripping' is, of course, the normal operating limit of the booster;

and I wished to emphasise that this current - which, if an adequately rated booster/supply is used, and is ONLY likely to be experienced in a fault condition - such as short circuit across the rails somewhere - is dependant on the size of the booster (therefore scale related) as well as the wiring used.

 

For PROTECTION to WORK, it is essential that the SHORT CIRCUIT CURRENT the layout wiring can support (by having a low enough wiring resistance) is considerably more than the 'booster normal maximum'.

 

Eg: a 1 Amp limit and 10V track voltage requires a resistance of LESS THAN 10ohms

a 2 Amp limit and 10V track voltage requires a resistance of less than 5 ohms

a 5 Amp limit and 10V track voltage requires a resistance of LESS THAN 2 ohms

I=V/R a 10Amp limit and 10V track Voltage reqires a resistance of LESS THAN 1 ohm but

a 10 Amp limit and 20V track voltage requires a resistance of less than 2 ohms (eg G Scale)

 

(Consider this when using an 'analogue layout's wiring for DCC: Okay with a 2A controller, but not for 10A controller!)

 

However, it is NOT true that a 'short circuit' should ALWAYS cause the booster or controller to trip! That response is heralded by analogue-advocates as a reason for NOT going DCC! - the 'Everything Stops for Tea a Short syndrome.

 

A 'Short circuit' may be momentary, and caused by capacitors in a sound-fitted loco, for example, creating a large inrush current. Equally many Auto-Reversers rely on detecting a Short-circuit as the loco wheel bridges the join at one end of a reversing loop. For correct response, intelligence is required: a booster will accept the higher current for a set duration, which needs to be longer than the time taken for the Auto-Reverser to Flip and remove the short-circuit condition, or for the loco capacitor to charge. Using breakers like the PS-X series, in between the Booster and its Power District; by creating 'sub districts', both a lower value of fault current can be set, but also the intelligence of allowing capacitor surges. This is combined with 'automatic re-trying' which switches the power back on at 1 second intervals - allowing automatic restoration

when the fault is cleared - without the operator having to physically return to the controller to Reset.

 

ONLY IN A [sEVERE:] CONTINUING FAULT do I expect any of my boosters to trip, and therefore require manual resetting.

 

If Progressing from a 'low power' output controller: buy an add-on booster for the track power, and then use the original output for the Accessory Data Bus to your Points and Signals (negligable current when used with LS150 decoders and similar, which use a spearate 50-60Hz 16Vac supply for their point-motor power. Then a short on the track will/can leave the accessory bus still operational; perhaps to change the overrun live frog point, and remove the short.

[Steve Claud]

Hello everyone

 

I've read this and many other threads but living in rural France I'm a little restricted in what I can purchase (except of course for mail order).

 

Please could anyone confirm if I've bought acceptable wires as follows:

 

Bus: HO7 V-U 2.5mm² (Max 3500W FUS 20A)

Droppers: HI-FI 03VH-H 2 x 0.75mm² 

 

(I'm not sure if the reference numbers will mean anything to anyone but for completeness I've included everything)

 

Regards

 

Trevor

[Crosland]

It would help to know whose reference numbers they are, but a simplistic reading would suggest they wil be OK.

 

I am hoping the 3500W is a "foreign" way of saying 3500V and relates to the insulation break down voltage.

 

If the 3500W is a power rating then that would ring alarm bells for me. I would not buy cable from anyone quoting such, as it shows a staggering level of ignorance about how cable is specified.

 

Andrew

[Steve Claud]

Thank you Andrew for your response which is very helpful. They are manufactured by "Electraline" and I bought them from "Weldom" which is a large nationwide DIY store here. The 2.5mm² wire is sold for equipment des circuits des locaux d'habitation.

 

Regards

 

Trevor

[rob D2]

Sorry to resurrect this old thread but I need some advice on wire.

 

I've always used reels of multi core from model shops but recently run out.

 

The only thing my local maplins had that was close was single core " bell wire " which looks about the same diameter .

 

I'm running prodigy advance DCC and this is for the droppers. Do we think it'll be ok ??

[Junctionmad]

Sorry to resurrect this old thread but I need some advice on wire.

 

I've always used reels of multi core from model shops but recently run out.

 

The only thing my local maplins had that was close was single core " bell wire " which looks about the same diameter .

 

I'm running prodigy advance DCC and this is for the droppers. Do we think it'll be ok ??

 

7/0.2mm is "OK " for short distance 00 droppers , 16/0.2 is better 

 

wouldn't use bell wire even for bells, horrible stuff 

[AndyID]

Sorry to resurrect this old thread but I need some advice on wire.

 

I've always used reels of multi core from model shops but recently run out.

 

The only thing my local maplins had that was close was single core " bell wire " which looks about the same diameter .

 

I'm running prodigy advance DCC and this is for the droppers. Do we think it'll be ok ??

 

If you are only using it for droppers that are a few centimeters long, electrically, it won't make the slightest difference. They all have resistance of less than 0.1 ohms per meter. The solid bell wire probably has the lowest resistance, but you might find it a bit more difficult to work with and it might tend to break if it's subject to a lot of flexing and vibration.

[Brian]

Sorry to resurrect this old thread but I need some advice on wire.

 

I've always used reels of multi core from model shops but recently run out.

 

The only thing my local maplins had that was close was single core " bell wire " which looks about the same diameter .

 

I'm running prodigy advance DCC and this is for the droppers. Do we think it'll be ok ??

Hi

If you need to use Maplins and they are rather expensive compared to other suppliers like Rapid or CPC etc then look for the Maplin part numbers in bold for the wire colours stated.  Ideal for DCC dropper wires.

Also use 16/0.2mm wire for all solinoid point motor feeds and return (or use a larger wire).

16/0.2mm equipment wire Red PA71N  100Mtr reel

16/0.2mm equipment wire Red FA33L  10Mtr length

16/0.2mm equipment wire Black PA64U  100Mtr reel

16/0.2mm equipment wire Black FA26D  10Mtr length.e

Other colours also available.

 

Minimum size I recommend for a DCC bus...

32/0.2mm equipment wire Red XR36P  per Mtr

32/0.2mm equipment wire Black XR34M  per Mtr

Other colours are available but not that many from Maplins.

 

For smaller wiring jobs then 7/0.2mm is suitable lighting of buildings/colour light signal feeds etc or for droppers where every section of track has a dropper and none are longer than 300mm bus to rail. (These are my recommendations)

7/0.2mm equipment wire Red PA52G  100 Mtr reel.

7/0.2mm equipment wire Red BL07H  10 Mtr length.

7/0.2mm equipment wire Black PA45Y  100 Mtr reel.

7/0.2mm equipment wire Black BL00A  10 Mtr length

Other colours also sold.

 

 

Post edited to correct typos!

Edited April 6, 2017 by Brian

[Phil S]

OP: HO7 V-U 2.5mm² (Max 3500W FUS 20A)

       Droppers: HI-FI 03VH-H 2 x 0.75mm²

 

It would help to know whose reference numbers they are, but a simplistic reading would suggest they wil be OK.

I am hoping the 3500W is a "foreign" way of saying 3500V and relates to the insulation break down voltage.

 

If the 3500W is a power rating then that would ring alarm bells for me. I would not buy cable from anyone quoting such, as it shows a staggering level of ignorance about how cable is specified.

 

Andrew

Phil: The meaning  and description of the cable rating is quite clear!  it is for 2.5mm2  cable - the (French equivalent) of what we would use for a spur, or half a ringmain.  Remember that it is being sold 'domestically' for 230Vac use - and the description is simply saying that it is rated to be used with equipment taking upto 3.5kw   ..... and that a 20A fuse is the maximum which should be installed  to portect it.  [ Star wiring - not a RingMain ]

HO7 V-U will identify the manufacturers specification of the wire/cable.

Remember that cable rating depends on how it is installed - household wiring is assumed to be buried in a plaster wall which reduces the heat loses for the cable, and therefore lowers the maximum safe current.  I don;t know about French woring regulations - but it might be assuming surface wiring and that would explain a higher 20A rating being quoted.

[The Fatadder]

7/0.2mm is "OK " for short distance 00 droppers , 16/0.2 is better 

 

 

A silly question,

 

What exactly is wrong with 7/0.2, and why is 16/0.2 so much better?

[AndyID]

A silly question,

What exactly is wrong with 7/0.2, and why is 16/0.2 so much better?

It isn't. There's nothing wrong with 7/0.2 for droppers.

[The Fatadder]

It isn't. There's nothing wrong with 7/0.2 for droppers.

Ok, perhaps the question I should have asked is why should the droppers and bus be different. I assumed (wrongly) that the voltage was going to be similar throughout the circuit.

[AndyID]

Ok, perhaps the question I should have asked is why should the droppers and bus be different. I assumed (wrongly) that the voltage was going to be similar throughout the circuit.

Ah! It's because the droppers are short and the bus is long. All wires have some resistance and when current flows to the locomotive that resistance reduces the voltage arriving at the locomotive. The effect is called "voltage drop" and it's proportional to the length of the wire.

 

The thicker bus wire has less resistance but the thinner dropper wires are short enough to not cause a problem.

[The Fatadder]

Ah! It's because the droppers are short and the bus is long. All wires have some resistance and when current flows to the locomotive that resistance reduces the voltage arriving at the locomotive. The effect is called "voltage drop" and it's proportional to the length of the wire.

The thicker bus wire has less resistance but the thinner dropper wires are short enough to not cause a problem.

I see, so if you have say an 18ft layout with 3 locos running on it wired with 7/0.2 (bus and droppers) the problem would be at the extramarital points away from the main feed you would have a significant voltage drop (resulting in loss of speed and potential interruption of signal to locos?

[Enterprisingwestern]

I see, so if you have say an 18ft layout with 3 locos running on it wired with 7/0.2 (bus and droppers) the problem would be at the extramarital points away from the main feed you would have a significant voltage drop (resulting in loss of speed and potential interruption of signal to locos?

 

Think of it as water down a pipe, the further it has to go and the more draw offs it has to feed then the bigger the bore it needs to be. (How we were taught about power supplies at the Gas Board many moons ago, but still basically holds good.)

 

Mike.

[The Fatadder]

Thanks. I think a rewire of the bus might be in order!

[AndyID]

I see, so if you have say an 18ft layout with 3 locos running on it wired with 7/0.2 (bus and droppers) the problem would be at the extramarital points away from the main feed you would have a significant voltage drop (resulting in loss of speed and potential interruption of signal to locos?

 

That's the general idea, although it's a bit more complicated than that with DCC.

 

Copper 7/0.2 has a resistance of around 0.08 ohms per meter, so for 10 meters (the distance is doubled because the current has to make a round trip out and back) and a current of 1 amp the total voltage drop would be 0.8 volts. It will be less than half that with 16/0.2

 

The idea with bus systems is to make them hefty enough that you don't have to be concerned about voltage drops at all. Other than the increased cost there would be nothing wrong with using heavier gauge wire than 16/0.2 for the bus.

[AndyID]

Thanks. I think a rewire of the bus might be in order!

 

That may not be necessary. It might be OK as it is. You could also just "beef-up" the longer runs of 7/0.2 by adding another 7/0.2 or 16/0.2 in parallel.

Edited June 17, 2017 by AndyID

[The Fatadder]

That may not be necessary. It might be OK as it is. You could also just "beef-up" the longer runs of 7/0.2 by adding another 7/0.2 or 16/0.2 in parallel.

Thanks

 

Once I get the fiddleyard wired up and connected to the rest of the layout, I will do some measurements I think and check that the voltage drop is acceptable across the whole layout. I think I will also add a few extra parallel feeds from the control panel to the droppers to beef it up a little (and connect the main wires to the fiddleyard direct to the panel rather than to the existing wires)

[AndyID]

Thanks

 

Once I get the fiddleyard wired up and connected to the rest of the layout, I will do some measurements I think and check that the voltage drop is acceptable across the whole layout. I think I will also add a few extra parallel feeds from the control panel to the droppers to beef it up a little (and connect the main wires to the fiddleyard direct to the panel rather than to the existing wires)

 

Sounds like a good plan. You will need to draw current through the system by attaching some sort of load when you are measuring the voltages. You also might be able to measure the feed resistances directly with a digital meter.

[Phil S]

There are 2 main criteria for adequacy of wiring ...In this case with DCC..

1/ under expected load of many / maximum trains running, that the voltage drop is minimal so that it does not cause... particularly for sound decoders.... to drop out... An NMRA spec is a minimum of 7V for a decoder to work.... But you might be starting from 12v 16v or 22v ( the latter more likely with larger gauges ) best to only drop about 2-3V under full load.

 

2/ the 'coin test' or short circuit test.... ( eg a coin on the track): this depends on the maximum normal current capability of your controller.... Eg 1A. 3A. Or 5A. Even. 10A in larger gauges..... The short circuit overload trip current will be HIGHER than this..... And so, as maximum controller current is increased,, the quality of the wiring MUST be improved to match.... To ensure that a short in ANY part of the layout WILL trip the over current protection.

 

Note that using sub districts with individual protection beyond from a PSX intelligent breaker.... The section beyond the breaker only needs to be sufficient for the breaker's limit!

 

This is why the is no single answer to what size wire is needed.... It depends on your present controller, and is your responsibility to get right for safety reasons.

Edited June 17, 2017 by Phil S

[john new]

On 09/05/2011 at 13:06, Gordon H said:

Rather than choosing according to 'Size', a better approach is to choose by 'Rating'.

The type of insulation used on the wire also has a bearing on this, but for the most part we would be dealing with PVC insulation.

7/0.2 is equivalent to 24AWG, and is normally rated at 1.4A

16/0.2 is equivalent to 20AWG, and is normally rated at 3A

Note that the current values shown at the Wikipedia link are Fusing Currents, i.e. the current at which the copper wire itself would get hot enough to melt and go open circuit . Not recommended for model railway use!

The normal ratings are much lower because they take into account the limitations of the environments for which they are intended.

 

A bit of a novice regarding amperage/wire gauge but understand the circuitry. I am wiring a small layout for either DC or DCC use depending on which controller is connected. Therefore traditional switched sections for DC and everything on for DCC.

 

I also have lots of 7/0.2 wire in stock, ok for DC but most guidance is not thick enough for the extra power (Amps) of DCC. The common return side no issue, I used stripped out mains cable for the bus wire, with short droppers to each rail section.

 

Now about to wire the switched side, if I use double wires for each connected section will the doubled thickness of wire be up to the job for DCC?  Max run will be about 3ft, most much less. 

 

This wire weight issue is the one that seems to generate the most opposing views hence asking the question.

 Most of my locos are currently analogue but DCC use will increase as more get chipped.

Edited May 15, 2019 by john new

[Phil S]

The size of YOUR wiring depends primarily on the continuous MAXIMUM output your controller is CAPABLE of ....because its trip-current will be higher still !! 

A DCC layout with a 1A controller has a different requirement to one with 3, 5 or even 12A controller!!!...... ( and is then  made easier by having breakers protecting 'sub' districts 9r  areas.)

 

Whilst, with an analogue layout, you would/might  simply 'turn up' the volts, if 'wiring resistance' was seen to be slowing a train down, DCC uses an 'unchanging' fixed voltage on the track ( of about 15-16V ac data-modulated square wave (max22V  ) .... And therefore if parts of the track experienced more resistance, the train would slow, and possibly lighting dim ..... In a Very extreme case, ( perhaps a loose fishplate ) the available voltage could fall below that needed to maintain the sound or (microprocessor) control .,.. Causing sound to stop and restart or the locodrive itself to faulter.

  (And as the controller is effectively in the loco, it is a potentially similar effect to everyone cooking Xmas turkey at the same time and Mains voltage dropping everywhere)

So the initial requirement is to ensure the adequacy of the total wiring loop from controller to distant loco.  In analogue this was probably a whole set of individual 'loops' ...1 for each 'section'.  In digital use, the individual sections are not needed (in the same way) and multiple trains mày be present in any 'wiring loop' ..... And from V= IR ,  the more current being taken in the loop, the more the voltage drop for the same wiring resistance. ( Some short lengths can be thinner than the remainder such as 'droppers'.….... But as short as possible to minimise their resistance)

 

How much current might continuously flow in a loop section of your layout depends on the MAXIMUM continuous output of YOUR CONTROLLER...which was probably 1amp for analogue, but might be 1, 2 ,3,4,5 8 10 or even 12A  in a digital layout.  ( like household wiring ...individual areas may be fuse/breaker protected to have only lower current limits ).  This has a MAJOR effect on the wiring you need!!!!

 

For YOUR protection, the controller has a cutout which will operate when the current exceeds a certain amount which is ABOVE the continuous maximum.  The higher the maximum continuous output of your controller, the higher the short-circuit overload current tip will be ..... And the resistance around the loop needs to be low enough to ensure that amount of current CAN flow .... Even though it is only for a moment.

 

Therefore test ALL reaches of your layout with a local short-circuit across the track, and confirm that the controller ( or area's circuit breaker, if sub divided ) trips out.

The latter, as with house wiring divided into separate parts each protected by a fuse/  breaker, is a much better situation experience, as the remainder of the layout can continue working as normal.