We supply and install DCC equipment into all gauges and scales, down to some larger 'N' Gauge models, from all main manufacturers including market-leading ESU LokSound and Zimo Decoders and other parts, and ECoS controllers.

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DCC, like all consumer electronics, is subject to ever-increasing change. This guide to DCC shows how a beginner can find a way though its complexities, and be successful in enjoying its huge advantages on any layout – small or large.

A Guide to Digital Command Control (DCC)

Christopher Tanous

This description of DCC gives a beginner's guide to this splendid and fairly new control system for electric model railways.

I once knew very little about DCC - hence I have written this for fellow beginners based on what I have learned from our Technical Director, Andy Harris, over the seven years since we founded DCC Fitting Limited together, mainly to equip customer's models with DCC. I have a very high opinion of Andy's expertise with all things mechanical and electronic; indeed I have gone so far as to say to one or two people lately that Andy must be the best DCC man in the UK - if not in the World! Andy has checked this article to avoid any technical inaccuracies, but I must point out that any views expressed are my own.

At DCC Fitting we are real fans, and do the highest-quality work; our workmanship is fully guaranteed. All work is done by Andy Harris at his home in Weston-super-Mare near Bristol. He is not himself a railway enthusiast, but ensures that the 'chuff rate' emitted by a steam locomotive does match its wheel revolutions, and that brakes squeal as an engine/train stops, and not earlier or later!

I am the Company's Managing Director, and undertake all its accounting and administration at my home nearly 40 miles away from Andy's; I see him face to face only occasionally, but we exchange e-mails and talk on the 'phone daily.

I am a long-term railway enthusiast, both of model trains - which I have had all my life - and I am also an experienced amateur railwayman. I 'learned the ropes' on the footplate and in signal boxes (almost entirely unofficially) in the last 10 years of steam on British Railways from 1958 to 1967, and have worked on 'heritage' preserved locomotives since 1966, now being a qualified steam and diesel driver. I have published two books about my experiences.

Professionally, I (now retired) was once a magazine journalist - with my first job in journalism being on the editorial staff of a now defunct model railway magazine published by the well-known Ian Allan transport publishing group, before I went on to work on a serious financial magazine; later I became a marketing and PR consultant, owning and running my own agency. In the late 1970s and early 1980s I was the Editor of the bi-monthly magazine The Gauge 0 Guild Gazette for several years.

DCC is not cheap

A word of warning must be sounded - DCC is fairly expensive. After all, one is equipping each loco with its own individual controller, and almost all of them also have a synchronised and accurate soundtrack on board as well. Such things cannot come cheap - and fitting them properly is quite tricky! Control systems are constantly evolving, and developments in electronics have made a big difference. DCC was first developed as a standard in the USA by the National Model Railway Association (NMRA), and was then quickly adopted in Europe and in the rest of the World. DCC has become ever more popular in recent years, and most 'serious' railway modellers now use it.


It is always dangerous to say that perfection has been reached, but DCC is close to it. It is one of the only two systems we know of which enable each loco to be driven individually, independent of all others very near it. The other such system is Radio Control, also available for all scales and gauges, but most often found on large-scale garden railways, with its engines often powered by batteries.

Mass production manufacturers do market 'cheap' DCC systems (quite often under proprietary names), but these do not provide 'proper' DCC with their sound often being rather 'tinny'. An early system was Hornby's now obsolete 'Zero One', which never really caught on. From time to time we are asked to strip out other systems, and to replace them with 'proper' DCC. There are also some 'cowboys' offering 'low-cost DCC'; we sometimes have to put their efforts right too.

To be frank DCC is quite expensive - but once used it is very hard to do without! In summary, it is better to have a layout of a simple country branch line with DCC control than a much larger layout without the benefit of it.

Model railways over the years

This is nowhere near a full description of how model railways have evolved, and what follows is very much simplified, only touching on the many different scales/gauges and qualities of the model trains which have been developed from the Victorian era to the present day (2020).

In this short account several gauge/scale combinations have been ignored completely, or mentioned only briefly. However, looking back over just the last sixty years, the model railway hobby has developed a lot in that time, and the finest layouts are now all but mistaken for the real thing, certainly in still photographs and even when seen in operation. One of the most significant developments has been increasing success in the creation in miniature of a faithful reproduction of the real railway, making the right noises and operating like the real thing.

The early days of toy trains

It was not very long after real railways first ran in the 1830s that toy trains appeared. The very first working model locos were developed in the 19th Century, were driven by live steam, and were almost never models of real prototypes. To the Victorians they were often known as 'Piddlers'. Scales and gauges started very large, since model trains were at first only available to the wealthy, who lived in large houses. Although many locomotives were driven by live steam, clockwork propulsion also became common. In this account we follow what has become everyday practice, and refer to both 'XYZ SCALE' and 'XYZ GAUGE'. The latter description is not really correct but is often used.

Before the First World War some enterprising manufacturers (many in Germany) began to sell models based on real prototypes, and electric control began to come in, sometimes even - horrifically - using full mains voltage all around the track! Quite soon common sense prevailed and 12 volts DC became a fairly standard operating voltage in Europe and in the USA, but almost always with unrealistic three-rail electrification. Early models were far from accurate - but as time went on some manufacturers modelled a particular railway company's engines reasonably well, but then offered the same thing in the very different liveries (colour schemes) of several other companies!

There were no widely accepted gauge/scale standards until the very well-known German manufacturer Märklin (founded in 1859 and still very active today) introduced Gauges 1, 2, 3, 4 and 5 in 1891, and modellers started to quote the gauge to express which size of model trains they had chosen for their own layout.

In the very early years of the 20th Century Märklin also introduced a new scale, called 0 Gauge (but with a slightly wider track gauge than is now used). 0 Gauge became popular in the years before World War II, while very few people chose anything larger than Gauge 1. Gauges 1 and 0 are both popular in the UK today. (See below for more on Gauge 0.)

From the early 1920s H0 ('Half 0 Gauge') became increasingly popular in Europe and Worldwide, but never succeeded commercially in the UK. It was first introduced in Germany as the 'Tabletop Model Railway' (a term quite soon to be borrowed by Hornby in the UK, see below.) H0 is now the most popular gauge and scale in the world, and is used by all manufacturers of European- and American-outline models.

In the 1930s Hornby (an offshoot of Meccano) manufactured some attractive near-scale 0 Gauge models (7mm to 1ft scale), but running on 32mm gauge track, which strict purists regard as being slightly too narrow. These models (some now very valuable) were mainly clockwork-driven, but some had electric motors. In the UK in the late 1930s the company also began to make mainly electrically-driven '00 gauge' running on 3-rail track to the HO gauge, but with a 4mm to 1 foot scale body on a 3.5 mm scale chassis; Hornby launched its own 'Table Top " Railway', coining the name 'Hornby Dublo', which caught on. For the first time Everyman could afford a model railway layout.

While using the same track gauge (of 16.5mm) as H0, Hornby chose to make the superstructure of its models of the slightly smaller UK locos to a marginally larger new scale of 4mm to 1 foot, so as to be able to provide enough room to fit in the large electric motors of the day, while manufacturers of models of Continental and American differed by managing to make the superstructures of their slightly bigger prototypes to the smaller scale of 3.5 mm to 1 ft, maintaining the scale of the track gauge. Both H0 and 00 gauges became standard, and remain so today, despite the minor inaccuracy of 00 gauge.

Higher standards of accuracy and two smaller new sizes

Hornby still made some very toy-like clockwork Gauge 0 models in tinplate for quite a few years after the end of World War 2, but from the 1960s onwards the increasing use of plastics by manufacturers enabled greater modelling accuracy. Most model railways standardised on 2-rail electrification, even Hornby Dublo following suit, with its former three-rail system becoming obsolete; in recent years the range of good quality and faithful models of an expanding range of prototypes has expanded greatly.

In the late 1950s 'TT Gauge' of 3 mm to 1 ft was launched in the UK but never really succeeded here commercially; it is not readily available, and is now a specialist interest.
However, the tiny 'N' Scale, with models at only 2 mm to 1 ft and with a track gauge of just 9 mm was launched in the UK in quite recent years; it has become very popular. It is not the smallest size available commercially, but is the very smallest into which DCC components can be fitted. Often these are special 'micro decoders', made very small to fit many (but not all) N Gauge models.

DCC Fitting has never been asked to deal with a TT scale model; one ought be big enough to present no technical problems, although some of the 'micro-components' developed for N Gauge might have to be used.

Control systems

The 'conventional' system of model railway electrical control developed during the first half of the 20th century, and by the mid-1960s was largely standardised worldwide (both in 00 and 0 Gauges), as two-rail operated with 12 Volts DC, usually converted from mains voltage by a transformer/rectifier, although batteries are sometimes used.

The speed and direction of locomotives is controlled by varying the voltage and polarity supplied through the track; this system has served well, but at least one extra controller is needed to allow more than one engine to move at the same time. This, and the need to divide the layout into a number of electrical sections makes it very difficult, for example, to do what the real thing does all the time, eg moving one loco up to one or more others which are 'stabled', ie parked. DCC enables this, because every engine (or Motive Power Unit - MPU) uses the same constant voltage of 15 volts AC in the track, but its decoder is individually controlled, even to being able to sound its own whistle, once its unique identity number has been entered into the master controller.

There are a few 'purist' groups - eg the 'EM Gauge Society', which insists that 4mm scale track should have a gauge of 18.2mm (exact scale for the prototype's 4ft 81/2 in) - but most people stick to the well-established '00' running on track of 16.5mm gauge - and nowdays there are dozens of excellent and accurate Ready-to-Run (RTR) 00 gauge models of real locomotives and rolling stock on the market. Nearly all 00 gauge RTR locos are now sold as being 'DCC-ready', with a socket into which a DCC-decoder can be plugged. This does not make the engine entirely ready, especially if sound is required, but it does help by reducing the need for wiring and soldering. If there is no ready-made DCC slot, decoders can almost always be fitted, but need to be 'hard-wired'- ie soldered - into place.

The other popular size for a group of dedicated modellers, in the UK especially, is the larger 0 Gauge, to a scale of 7mm to 1ft. There is some demand for conversions from 00 to EM gauge, or from standard 'Finescale' 0 Gauge to 'Scale 7 standards'. DCC Fitting can undertake such conversions.

The survival of 0 Gauge

The 'Gauge 0 Guild' (https://gaugeoguild.com) was founded just after the Second World War and is to be congratulated on ensuring that this 'premier' gauge survived, when it had all but died. Here I should declare a personal interest - having started as an 00 Gauge modeller, I now concentrate on 0 Gauge and am now building a layout in that size - with DCC control of course - closely based on a small area of the approaches to the engine sheds at Old Oak Common (BR Western Region - formerly Great Western Railway), where I was lucky enough to be a regular but unofficial visitor from 1961 to the end of London WR steam in early 1965.

On my layout I operate my growing collection of museum quality models of some of the real locos which I drove, mainly from Old Oak Common, around much of the Western Region in the London Area and as far afield as on the main line from Paddington to Reading, Newbury and Oxford.

General comments about DCC

DCC controls the complete layout

As mentioned above, the 'conventional' system of model railway control was developed during the first half of the 20th century, and by the Second World War was generally standardised at 12 volts DC. This suffers from the disadvantage that the layout must be divided into separate electrical sections. DCC MPUs still use 12V DC to drive their motor(s); the difference is that the decoder on board manages the conversion from 15V AC which is constantly supplied to the whole track.

It is possible to energise and control all electrically-driven parts of a layout - eg points, signals and even turntables - by DCC. Intermediate switches may be required.

It is important not to rely on 'rail joiners' to transfer electricity properly between each length of track, but to install a power 'bus' - ie two insulated wires carrying positive and negative traction current right around the layout, normally underneath the baseboard. Short 'dropper' lengths of wire are soldered to each length of running rail and from it go down to short gaps in the insulation of the 'bus' wire below, to which it is soldered. The cable used should be of sufficient amperage to carry the full current without losing any strength, and boosters may be required at the end(s) of a long layout to ensure that full power is available.

Wiring your layout

It is most important to recognise that the gauge of the current supply wiring to your track must be enough to carry the current required. Too many people wire up their DCC layouts with thin cable which is just not up to the job, then wonder why their system does not operate as it should.

DCC components

Every DCC-equipped MPU (steam, diesel, multiple-unit diesel or electric set, or other prime mover - eg a track inspection trolley) must have a 'decoder'. The simplest is the 'running-decoder', which converts the 15V AC track-power to 12V DC to move the unit in the right direction at the right speed. This decoder is 'addressed' by its unique number by the master controller, and it will then obey commands independently of any others. MPUs equipped to run using DCC can usually also operate on a conventional layout using up to 12V DC in the track.

DCC Sound

To make any sound, including the obligatory warning whistle (or hooter), a more expensive 'sound-decoder' and miniature loudspeaker must be installed and wired in. It is a common misconception that an original 'running decoder' which might already be fitted is retained, but it is in fact discarded (or occasionally can be recycled into another engine). Sound decoders with realistic sound requiring miniature loudspeakers are naturally more expensive, and are more 'fiddly' to install correctly. On a 00 gauge model of a larger steam engine, all these electronic components can be got into the boiler. Sometimes the tender and/or tanks are used as well. Just occasionally a very small MPU (say an 0-4-0 shunting engine) might need some of the DCC components to be fitted into a permanently coupled wagon or van.

An essential component is the soundtrack, down-loaded (or 'blown' in trade jargon) onto the sound decoder by one of a few specialist suppliers who make the recordings and use a special computer program to 'blow' them onto a sound decoder before it is fitted. Proper sound is originally recorded on top-quality equipment while riding on or standing near a preserved locomotive of the right class. But some prototypes (eg classes long since withdrawn) of steam, diesel and electric engines have not been preserved in running order, or - in many cases - at all. To get models of these engines to sound as close as possible to how they would have done, 'real' sound is used from a real loco of the same general type, including wheel diameter, number and size of cylinders etc (if a steam engine), and other dimensions.

Some, perhaps less scrupulous, suppliers provide 'generic sound' created by a computer.

£15 decoder v £35 decoder. As ever, you get what you pay for . . .

Inexpensive decoders will work - up to a point. But the cheaper ones tend to be unable to handle the power required to run even a short train, and there is a risk of 'frying' the decoder and rendering it useless. So please consult us first and don't buy on price alone. Call Andy Harris first - his 'phone number is 01934 510262, but please only ring him during our business hours of 8.30 am to 8 pm Monday to Saturday.

There are many new decoders coming onto the market but what we say is still true.

Some once-leading manufacturers have stopped any development; others, like ESU, continue to innovate and improve; this is why we recommend their components as a good choice for those starting in DCC. Some components are priced to appeal to the mass market, and only have very basic control functions with no room for expansion or for the finer points. It is a fact of life that the more expensive components give far better results. We will review your options with you and suggest the best solution, when we have established what you need. We will not try to pressurise you into the most expensive equipment for the sake of it.

Control - all makes available

At least one 'controller' with a transformer/rectifier is required to convert mains electricity into whatever form of energy is supplied to the model railway. At DCC Fitting we mainly recommend the use of the products of ESU, based in Germany, including their ECoS Command-Station, their 'Loksound' range of Decoders and their wide range of Loudspeakers. However we do occasionally recommend Austrian ZIMO components, or even sometimes a mixture of both. Our recommendation is sometimes dictated by the source of the correct sound.

We will also acquire and fit any other make of DCC component which may be requested.


DCC has the ability to control lighting, both all around the layout, in buildings, signals and coaches - and even on MPUs. Models of steam locomotives have lights, and quite often have a red bulb or two fitted into the firebox to reproduce the glow of the fire. Sophisticated DCC enables all these features to be operated independently; model diesel and electric MPUs should certainly include lights, which can be switched on and off individually.


We are not as yet convinced by any of the 'smoke units' so far on the market for model steam engines, and generally prefer not to fit them. This may change, but we are concerned about the potential cost and complexity of an adequate smoke generator, which needs to be synchronised with the driving wheels.

Fitting older models with DCC

Some quite old model engines will accept decoders etc, soldered in (i.e 'hard-wired') where a fitted 'plug-in' DCC socket is not provided, but model locomotive motor design has come on by leaps-and-bounds in recent years, and many older models are not suitable for DCC. It is unwise to purchase old models second-hand in case they cannot be modified - this includes for example the 'Hornby-Dublo Ring-field motor', much vaunted at the time of its introduction, but of which not all examples will accept DCC. Some more recent motors are also not suitable for DCC - even some of the early coreless, types. Split-chassis hand-built locos are not normally suitable; we must examine each one individually to assess it.

DCC Terminology

These descriptions have been written for those unfamiliar with DCC, which stands for Digital Command and Control. A brief description of how it came to be developed is in our longer Guide to DCC (above).

DCC can be fitted to Locomotives/Motive Power Units (MPUs) in all model railway Gauges and Scales down to and including some larger 'N' Gauge models (to 2mm to 1 foot scale). Some prototypes are too small to enable all DCC components to be fitted into 'N Gauge' models of them; quite often the tender is used on models of smaller steam locomotives, or an MPU can be equipped with a permanently-coupled item of rolling stock to carry any components too big to be fitted into the locomotive itself.

Track voltage

DCC is standardised with 15 volts AC being supplied to the whole track, which does not require any section switches. Many DCC-equipped MPUs will operate on conventionally controlled layouts.

Each individual MPU is fitted with a decoder, which converts the voltage into up to 12 volts DC. Each decoder is given a unique number (which is easily changed. Normal practice is to give each decoder an 'address' containing four figures, but avoiding initial '0's is recommended.)

The address often corresponds to some or all of the individual running number of an MPU - eg an ex-LMS 0-6-0 4F Steam Locomotive with a BR Running Number of 44132 could have a Decoder with the address '4132'. Once 'addressed', that model only will then respond to all 'commands' given by the Master Controller.

It is important to avoid giving the same address to more than one decoder.


1 'Running decoders'
This is the basic decoder; it is quite often factory-fitted 'inexpensively'. A running decoder will control the direction and speed of an MPU, and is in itself an improvement on 'conventional' control, which achieves directional and speed control by supplying variable current to the whole track, with section switches used to energise only the lengths of track on which an MPU is to run.

Running decoders normally include control of directional lighting automatically. They will also control (typically) up to 4 auxiliary 'Functions' (see below for more on 'Functions').

2 'Sound' Decoders'
This type of Decoder must be connected (normally by soldering a wired connection) to a loudspeaker. A number of specialist companies record often authentic sound from preserved examples of MPU types, but beware that some sound on the market is 'artificial', often being generated on a computer.

The Decoder itself is loaded ('blown' in trade jargon) with a soundtrack using a special computer program. A soundtrack will often include other features such as brake squeal and whistle sounds. These are brought into play by 'Function Keys' on the Master Controller - there can be up to 28 Functions on a Sound Decoder.

The loudspeaker and soundtrack plus the wiring harness and fitting costs can make it relatively expensive to equip an MPU with a Sound Decoder.


These can be numbered according to the owner's wishes, and are normally controlled by being selected by the Master Controller. Some controllers (eg the ESU model we recommend and supply) have some 16 'Function Keys' - more than enough for most users. Higher-numbered Functions can usually be controlled on other makes of controller by pressing more than one key at the same time (see the manufacturer's Operating Manual for details).

Sound files include a great many function - some (eg the noises of shovelling, for steam locomotives only) are included on most 'Sound Files' and many DCC users like them (despite their being unrealistic. Shovelling sounds would not be heard unless one was actually on the foostplate).


There is a wide variety of controllers on the market and most will operate decoders made by different manufacturers. All will control several Functions - some have separate numbered 'Function Keys' which control multiple Functions easily. If a controller has a limited number of 'Function Keys', additional Functions can often be switched on by pressing two or more buttons at once.

Setting up Functions in an MPU

Part of the process of setting up a model MPU to operate on DCC is to decide which functions one wishes to have and then to allocate a Function Number to each one. This is an individual choice, set up using special DCC software. We do this as a routine when installing Decoders for our customers, and we find that most of them are happy with a standard list of functions, as shown below:

F0 Directional lighting (automatic)

F1 The 'Chuff' Rate, synchronised with the revolution of the Driving Wheels (steam engines only - typically four beats per revolution).

With models of Diesel locomotives/Diesel multiple units there is a typical series of sounds, first the 'clatter' of starting up, followed by the rumble of an idling diesel engine, then the increasing roar as the locomotive moves off.
Examples of all these in action can be seen in the video on the Home Page of this Website.

F2 Whistle/Horn (short blast);

F3 Whistle/Horn (long blast);

F4 Blower (Steam); Air-brakes (Diesel) On and off;

F5 Shovelling sounds (Steam only)

F6 Safety valves (Steam only);

F7 Injector (Steam only);

F8 Ejector (Steam only);

F9 Guard's Whistle

F10 Coupling noises/Fan (Diesel only);

F11 Handbrake on/off

The above is a list of common functions. However we stress that it is not exhaustive, and is in an arbitrary order which depends on the personal preference of the operator.

'Stay Alive' has done away with flywheels

Stay Alive is the 'generic' term given to various types of Capacitor, which store a small amount of electrical energy enough to drive a short-wheelbase locomotive across an electrically-dead gap in the rails (often at a 'switch' or 'points') where its 'pickups' (current-collectors) lose electrical contact and the MPU would otherwise stall and get stuck.

This is one of the more recent developments in DCC. It can give short-wheelbase locos (eg 0-4-0T shunting 'Pugs') without sprung axles, the ability to store enough power electronically to get across places (eg points) where none of its wheels is in contact with an electrified rail. Larger engines with more electrical pickups should not need this.

Once upon a time the only solution to this temporary loss of electrical connection was to fit a heavy flywheel to the motor to keep it turning for the few moments while the power was lost; with Stay Alive such a space and energy-consumptive fitting is not required.


Tantalum is a very thin but strong metal, and its use in a Capacitor allows it to be very small. The single word 'Tantalum' is quite often used as a shorthand way of referring to this type of capacitor, fitted to small-bodied MPUs which cannot otherwise be equipped with Stay Alive.