Re: Sub Bus "beyond" Main Bus

Anthony Ashley <anthonyashley@...>

Dear Chris,


Your layout sounds very similar to mine. Mine is called Welsh Dragon rail is 35feet by 15 feet and is in N gauge. I spent 12 months planning and have built the boards for approx 1/6 of the layout. It has taken me 4 months of emails and research to sort out the electronics, which I think i have now cracked.


I have a thread at the following which you may be interested to look at as I have been asking many questions similar to your own over the last 4 months.


The thread is at : bothil/


You will find my wiring diagrams toward the end of the thread. I have slightly modified them and can send them to you in a more readable format if you wish to see them.


From my  research the sub bus and bus should be no longer that 30 feet in length. In addition I have read that there is a need to twist the pairs of wires  3 times every metre. It cann’t hurt to do this and is supposed to assist with impedance. You should also terminate the wires using a resistor between the wire pair to terminate them.


You may find the following web site very useful as I have used it extensively:


I contains much info on wiring and electronics.


On my layout I am having approx 7 power districts and 35 sub districts. Each sub district will have an on/off switch to isolate the sub district to assist with fault finding on the large layout. In addition every track will be wired into a terminal block so that I can disconnect any track to isolate faults.


If you wish to talk further please send an email and I can assist further if required.




Anthony Ashley




From: WiringForDCC@... [mailto:WiringForDCC@...] On Behalf Of cdrat72kingscc@...
Sent: Thursday, 16 January 2014 7:36 AM
To: WiringForDCC@...
Subject: [WiringForDCC] Sub Bus "beyond" Main Bus


I have a 3 tiered layout that is nearing the build phase after 2 years planning! I have approx. 700" of track to lay down and after reading through Wiring for DCC's web site I have designed my layout to use the Bus/Sub-Bus wiring scheme. The layout room measures approx. 16' x 21' and I am hoping to go with 2 Boosters for the layout. At least that is my current thinking as I will be running short trains - trams, subways and suburban trains with 2, maybe 3 passenger trains (7-9 cars w/ 1 Lok). All in all I plan no more than 6-8 in operation at one time.

I have drawn up my wiring diagram and limited my Main Buses to 30' max from Booster output to the end. What I am interested in knowing is: Can the last Sub Bus off a Main Bus run "beyond" the Main Bus (for instance if it is a 12 foot Sub Bus can it run out 11+ foot (allowing for some overlap with the Main Bus to allow connection to it) beyond that 30" Main length?

I ask! as I'm not an electrician and electrically it strikes me as I'm possibly pushing the envelope of the 30' max. of a Main Bus by doing this (my Mains will have RC Filters installed at their ends). However when I look at Mark Gurries "Dedicated Main Bus" drawing under "Block Wiring for Large Layouts" it appears that a Sub Bus does run past the end of the Main Bus (far left of this drawing).

Thanks for all the help WiringforDCC has already provided me and future guidance to come.  Chris

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