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The 2 Wire Myth

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BR42 View Drop Down
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Joined: 28 Nov 2009
Location: Auburn
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    Posted: 02 Aug 2013 at 7:25pm
Hello Everyone!

One of the big myths of DCC is that one needs only two wires to the track, and that is all.  Well this may be true, but only for very small layouts.  As mentioned in another posting, I finished the wiring of my layout, and looking under it, it only looks like there are still a lot of wires under the layout, so that the wiring resembles that of a conventional layout.  How did this happen?  Well, here are some reasons:

a) Track-power should be fed into the rails from a power bus about every 3' to ensure reliable operation and to avoid voltage drop in long runs.  So you have one or more power buses running under the layout.  In my case there are two since the stationary decoders are powered by there own bus.

b) Switches and signals.  These need to be wired to stationary decoders, and these should have their own bus.  Sorry, Viessmann, Roco, and Marklin, powering turnouts decoders from the track sounds like a great idea, and it definitely will reduce wiring substantially.  But from on operating view, powering switch decoders from the track is not a good idea at all.  Any derailment due to a wrongly aligned switch can cause a short in the track bus which will also paralyses any stationary decoder hooked up to it.  So one cannot throw the wrongly positioned turnout to take care of the short! 

On my layout there are 28 operational signals as well as 47 solenoid switch machines.  These are hooked up to Teamdigital decoders, namely 9 SMD8 and two SMD2.   The SMD8's have internal routing features, which make them great for almost all yard and station application.  They also work great if you want to throw signals in dependance of switches and vice-verse.  However, 75 solenoid switch machines add a lot of wires.

c)  House and street lights.  There are 138 light bulbs connected to three power supplies using slightly more then 7A.  The main part of the layout is supplied by two 12V 3A computer power supplies, the stub-end station by one rated at 12V 2A.  Believe me, these lights require a lot of wires.

So what do you save in wiring opting for DCC:

No block control wires running from the track to a central switch board.  No wires from the solenoids to the switch boxes.  No wires for track sections that can be turned on and off.    Adding these three items would easily double the wiring already needed for a), b) and c).  So converting to DCC will reduce your wiring needs by about 50%. However, 2 wires only --- no way.

Moreover, DCC makes it easy to wire sections of the layout independently just in case it needs to be moved.  I have about 10 Wires going across the two sections of the main part of the layout.  With conventional wiring, there would have been about 60 or more.

Finally, you do not have to throw block switches if you want to run multiple trains.  Digitrax says it completely accurately:  With DCC you run your trains, not your track.

Ulrich


Edited by BR42 - 03 Aug 2013 at 9:18am
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