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Combined running/programming track

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on a restart/rebuild of my DCC layout, I’m thinking I could have a short spur which could double as a programming track. I have a Prodigy Advance 2 with separate outputs for main and programming. So I’d want to be able to leave this spur as connected but switchable to either/or, but obviously not both. I have some spare switches but not sure what they are. Each has 6 terminals, and the switch throws up-centre-down. Am I safe to assume this will be on1-off-on2? So, with 2 wires from bus, and 2 from prog output, what is purpose of 6 terminals? Or is this not the right switch?
I’m sure this is a Simple question for many, so I hope you can explain.



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The spur should be completely isolated from the rest of the layout ie. both rails and needs its own feed. That feed should go to the centre terminals of a DPDT switch. The main feed should go to the two terminals on one side of the centre terminals and the programming feed to the other two. Just make sure the main feed is connected to the same rails as the rest of the layout otherwise you will cause a short.



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Its probably the right switch.   But I say "probably", and as Ian doesn't know, there is a bit of risk there.   Richard's description is correct if the switch is the right one.


The switch MUST disconnect before connection.  In switch terms that is "break before make".   A centre -off switch will meet that.   


Another risk of a programming "siding" is that something is left over the rail joint, bridging the two tracks together - a wagon with metal wheels,  or a loco moves when programming and goes across the join.    There are wiring ways to remove this risk with a dead-section between programming and main when set to "programming", it needs a four-pole switch.  

Or. the simple, safe, method is to not have a "siding" which connects with the main line, but instead a piece of unconnected track.  Then the mistake cannot happen.   (Have a model track gang on the scene with a length of rail removed, so it can't be driven over!).


Get it wrong and connect the programming and main outputs and it will damage the programming output of the system.



- Nigel 

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There's been a previous topic on this you may like to read and digest https://www.rmweb.co.uk/community/index.php?/topic/143258-fitting-programming-track-as-part-of-the-layout/&tab=comments#comment-3502480



As others have said, it can be a problem if safeguards aren't put in place.





Edited by mezzoman253
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Thanks for responses, and link to earlier subject.

I hadn’t thought about the double isolated section, to overcome risk of a metal wheel or pick-up bridging the single gap. Must say, I like the simplicity and effectiveness of the unconnected track with a work gang on site

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