DCC wiring made simple

[Des1707822314]

I have, in the past, re-wired an old house, got an A level in physics but DCC is a blind spot. I built my last layout over 15 years ago and it was analogue. I'm now building a DCC layout and I need some wiring advice.

I understand the principle of using a BUS and dropper wires. But, in three bears language, can someone tell me:

1. What size wire do I need for the bus
2. What size wire do I need for the dropper wires
3. Which clips are best for joining the wires
4. What do I do about points

Most of my track, rolling stock and locomotives are Hornby products.

[RDS]

Hi Des

The major difference between Analogue (DC) and Digital (DCC) is that with DCC, the whole layout is Live all the time.

In order to achieve this Hornby sell Point Clips (Part Number R8232). These are supplied in packets of 20 and 2 clips are required for every point on your layout. These clips ensure that when a Point is switched, the power to the siding (for example) is not cut off.

With regard to Bus and Bus droppers, these are not strictly required and I have previously operated a layout with 4 concentric loops and over 20 sets of points, with just one connection to the whole layout without a Bus or Droppers at all.

Having said that, a Bus and Droppers are recommended to ensure full voltage all around your layout. Different members have different views regarding wire size, but when I did eventually fitted a Bus, I used 2.5mm Cable stripped from Mains cable for the Bus and 1.0mm Cable stripped from mains lighting cable for my droppers.

All my joints are soldered, which is preferred to connectors.

[Rog RJ]

How big is your layout? This could affect the recommended wire size.

What controller? This could also affect wire size.

Droppers use either 7/0.2 or 16/0.2

There's a whole variety of connectors that work well but soldering is best IMHO.

What make and model of points and point motors?

[96RAF]

I also used ex-mains wires for my bus - solid core wire is OK for the main bus as it does not move.

For droppers I use ex-mains twin-core flex. Multi-strand because it can move or can be disturbed.

I use Brimal CN165 junction boards to connect my droppers and bus wires. I have five of these around a single garage sized layout.

CN165 Power Distribution Board 18 way Screw Terminal Connection | Brimal Components (bclstore.co.uk)

From the controller a pair of bus wires leads into the board and out to the next one and so on. At the end of the bus I have a terminator to suppress any voltage spikes. Dropper wires are soldered to each track piece and connected to the 'pos' and 'neg' terminals on the board.

My points are powered form a second controller over a second 'Accessory' bus.

You can power your point decoders from your track bus but this eats into your available track power, so a separate bus is preferred.

[Des1707822314]

Thanks to you all for the replies.

My layout is 8ft x 4ft and is controlled with a Signatrak

[morairamike]

My layout is basically 2½ loops plus a shed yard. There is an access flap roughly half way around. So from my controller base station I run two busses, one clockwise, one anti clockwise. This is mains cable stripped out of the outer insulation, but left in the individual insulation. The earth wire is discarded. These two wires are twisted every so often. They are attached under the board by cable ties and bases. Every piece of track no matter how short has a pair of droppers soldered to it mid point. These are 7/0.2 multi strand wires, red and black. These are soldered to the buss wires after the insulation is removed, as required. All my points are Peco electro frog, thus eliminating the need for the point clips. One section of my track is a twin track girder bridge, the buss wires to that are fed thru a single Hornby loco to tender 4 pin plug/socket, at one end, so the bridge can be removed easily. I have to date not had any problems using this method of track power application to the bridge. There are no fishplates on the bridge.

[Fishmanoz]

DCC Point Clips are only needed where you don’t run a bus and droppers. You don’t need both no matter the point types you decide to use.

[ColinB]

I don't know what the concern is with DCC, I use the same wire on my DCC layout as I did with my DC layout. Initially my layout was DC with isolating sections controlled by a 4 track DC controller. For DCC I just paralleled the four sets of wires together. My layout is 16 foot by 10 foot and I use 7/0.2 wire basically because it is flexible. I suppose as it initially was 4 tracks each supported by its own wiring system, then the only time you get the big currents is where I have paralleled them together where I use thicker wire. I imagine as DCC is a reasonably high frequency signal you could have to start worrying about transmission line theory, but I have not noticed any signal loss of my layout and really you don't want to go there. If I remember the limit for CAN which is a similar type of system, is 2 metres so the best idea is to feed power from a single point radially so you do get any excessively long runs of wire. The biggest issue is probably capacitance so direct wiring to the track is probably preferable.

[Fishmanoz]

Colin, you are correct about starting to think about transmission line issues at your layout size. I’m sure Chris has given the link to the definitive source on this for DCC since you’ve been a member, and may do so again with this prompt? It is definitely not an issue on an 8 x 4 though.

And the consequences for larger DCC layouts? Use terminators and include twisted bus pairs.

[Flashbang]

The "Concern" is two fold with DCC Bus wiring...

A) Bus wire size used MUST be able to handle the maximum current output of the DCC system. Typically 4Amps or more. (DCC at 4Amp is 64 watts of heat/power!)

B) Getting fault currents back to the DCC system unhindered, usually caused by too smaller wire size used or too much reliance placed on metal rail joiners and the result is a failure or delay in tripping the system.

DCC Bus pair IMO needs as a minimum to be 32/0.2mm flex wire or 1.5mm2 solid (Solid is usually stripped from former mains lighting cable outer sheath). Droppers between Bus and rail can be either 7/0.2mm or 16/0.2mm wire. I would recommend 7/0.2mm be used where plenty of droppers are installed - perhaps one pair per rail section and keeping their length to a maximum of around 350-400mm bus to rail. Increasing the Dropper wire size to 16/0.2mm allows longer dropper wire length (approx. 500mm) and if wished less frequent droppers installed.

Reliance on metal rail joiners (metal fishplates) passing power and data is really the weak link in the connection chain.

The most serious check a DCC user can undertake is the 'Coin across the rails' test carried out at several places around the layout. This is to ensure the DCC system trips out as it should do with each dab of the coin across the rails. Any failure to trip or delayed/slow tripping needs urgent attention as to why the failure is occurring and quickly correcting.

But of course there will always be someone who says "Well my layout works with xxxxx" Replace xxxxx with Bell wire, Telephone wire, Wet string etc. But the text I've placed above is best practice and a proven means of ensuring all is correct. Remember, it can never hurt a circuit by having too larger wire size, but undersize wire can and will probably lead to issues at some stage!

For a simple train set forget all the above. Just plug the DCC console into the track connector and play. For those who want a more permanent model railway or those who have a larger permanent layout, then whenever possible follow Best Practice! :-)

[Flashbang]

Oh I nearly forgot!!! CAN (Controller Area Network) will operate on wire up to at least 500 Mtrs in length.

A read of this free to download MERG book will provide much information... https://www.merg.org.uk/content/ebook

and a view of Dave Fenton's video using a CAN network

is worthwhile too.

Mod message: Above URLs converted to clickable Hyperlinks

MERG - Electronics for Beginners Book

[Flashbang]

Thanks Chrissaf for the URL corrections and active links. grinning

[Chrissaf]

Moderator message: This post was originally posted by Des in a new duplicate thread. It has been re-pasted below as it really is a continuation of this thread.

Thank you all for your excellent advice. I now know what to do.

Regards

Des

[Aussie Fred]

A question I have asked before and haven't got an answer to is "when I have 3 tracks running along side each other do I have to have a bus wire for each track or can I run droppers from each track to the same bus wire"?

[Flashbang]

You only usually have two main Bus wires (the DCC Bus Pair) feed from the DCC Consoles Track output. Onto these two bus wires connect all rails via smaller wire sized Dropper.

So in answer, only one bus pair and all tracks connect onto that bus pair. Ensuring all left hand rails connect to the same bus wire and of course all right hand rails to the other bus wire. grinning

[96RAF]

You can connect the droppers from all three tracks to your bus wires. A power bus is usually a single pair of wires, but may be in the form of an open ended loop, a T shape with the controller placed centrally or radial i.e. several shorter bus starring out from a central point connected to the controller.

All these bus variants are illustrated on Brian Lamberts web site mentioned previously.

Edit - today seems to be my day for posting just as someone beats me to it.

[Chrissaf]

Yes when using DCC control.

In DCC all track is live all the time and ultimately connected to the same controller. The only reason one would have multiple BUS wiring runs each serving different sections of track would be for a large layout where you were employing multiple DCC power domains. For example used with DCC Boosters or where an isolated track section was being powered via a Reverse Loop Module [RLM].

In general, since all droppers would normally connect back to a common BUS connected to the originating DCC controller, then droppers from multiple loops including also sidings etc can all connect to the same pair of BUS wires.

EDIT: 'Ditto' FB & Rob posted whilst I was still typing my reply.

[Aussie Fred]

Thank Fellas, That puts my mind a rest as I progress through my wiring. I am aware of the need to have a left and right wire (red and black). I plan to go half way round my track to the left and half way round the tracks to the right. (my controller is in the centre). I am assuming I have to put an isolating join where the two meet so my decoder doesn't get confused if one signal is a fraction slower than the other.

[96RAF]

No join required at the bus ends Fred and no insulating joiners required at the rails (oddly enough).

Depending upon how long your bus arms are you may want to terminate each end with a bus snubber (also known by other names).

[Mac-_-]

Oh I nearly forgot!!! CAN (Controller Area Network) will operate on wire up to at least 500 Mtrs in length.

 

 

Really in interesting video Brian, wonder how far it could go. Probably cost a fortune in wire to find out ;). Mind five hundred metres is a right length.

[Mac-_-]

Thank Fellas, That puts my mind a rest as I progress through my wiring. I am aware of the need to have a left and right wire (red and black). I plan to go half way round my track to the left and half way round the tracks to the right. (my controller is in the centre). I am assuming I have to put an isolating join where the two meet so my decoder doesn't get confused if one signal is a fraction slower than the other.

 

 

If your going left and right with your bus wire, i'd put some IRJ above where the two bus wire's running in each direction end. If you don't your only connecting the loop back up again and wasting your time spliting the bus wires. Your controller won't get confused, either way.

[Flashbang]

Whether the DCC power bus is run as a ring, a radial (end to end) or a star (Centre feed with bus wires radiating from the central place) matters not. It is the size of the bus wire used that really matters.

A ring or any other bus wire circuit configuration is used on a DCC layout it will not cause decoders to get confused!

IMO a ring, especially on larger layout, is really just a waste of expensive bus wire and not necessary when the bus pair of of the correct wire gauge size. grinning

[Mac-_-]

Most I know only split the bus wire too save four inches, they say you can do a lot with four inches, I wouldn't know thankfully. When I ask why they have their bus wire split, they just look at me as if I'm some sort of fool joy. I'm certain most don't know why they split the bus wire.

Your right on the bus wire size Brain, on this occasion size really does matter smiley.

[96RAF]

Argument rages over whether a bus should be an open or closed loop. The pure science is based on transmission line theory and practice in the 1:1 world not model railway bus lengths.

Model railway argument notes that the rails can be a closed loop but not the bus.

My track bus and accessory bus runs from the controllers around a single garage in a U shape. The track bus is connected across the near end removable section by teeing off the bus, so there is no closed loop. The far (and open) end of my bus is fitted with a snubber to damp any voltage spikes.

[Flashbang]

Hi Mac.

It's Brian not Brain, though actually I don't mind. smile

I sure, but unproved, that having a radial Bus pair never decreases the data flow but does allows Bus Terminator filters to be easily fitted onto each end of the DCC Bus pair.

As you say, "Size" (wire size) does matter with a DCC Bus pair of wires. sunglasses