2 DCC Wiring Questions - liftout bridge kill switch & multiple feeders per section

[stokesda]

Thanks for the responses, guys. I was aware that throttle buses can't be looped, but I thought the same might apply to power buses - I guess not, though. Also, I'm planning to have the kill switch knock out at least 2 feet of track on either side of the bridge, so it should be OK for the kind of stuff I'll be running.

[BR60103]

Watch out for those decoders that can overcome dirty rails and walk over pieces of paper -- you may need a longer block.
Since most basic DCC wiring books show 2 wires to the track, which is equivalent to a looped bus, I don't see the problem. I'm sure that they must mean the throttle bus. I know with computer wiring (coax ethernet) we had to have a resistance between the middle wire and the ground/sheath at the end to prevent signal reflection.

[Texas Zepher]

QUOTE: Originally posted by stokesda
1. My layout is a donut-style with a liftout bridge (actually a hinged drop bridge) allowing access to the center. I want to rig it with contact switches so that when the bridge is lowered, it will kill the power to the bridge and the approach tracks to keep any trains from falling 4 feet to their death. I've seen this done on DC layouts with lever-actuated SPST switches connected to one of the track wires. Question is for DCC, is it sufficient to have a single SPST switch attached to only one of the two track leads, or do I need one for each lead (or a double-pole switch)?

Yes, the concept of a complete circuit doesn't change just because it is DCC. If you remove power from one rail the train will stop. Just make certain the 'dead block' is long enough to allow for locomotives passing power through their own wheels.

QUOTE: 2. I have been told that it's bad to have your DCC bus wires in a continuous loop - that they should be broken up so the ends don't connect together. My question is that if you have more than one feeder per section of track, or if you have sections connected by metal rail joiners, it seems that there is a kind of loop right there, between the rails themselves, the bus wires, and the multiple feeders between the two. (I have a small layout and am planning on using only one booster and one "block"). Nothing I've read anywhere seems to say that I need to insulate the rails between every pair of feeder wires, but the whole "loop" thing just got me scratching my head. Can anyone shed some light on this? Is this a valid concern, or is it just my imagination?

I think there might be some confusion between the power bus for the track vs. the throttle bus. Throttle busses need terminators and loops are bad and might not even function if there is one (a loop). On a small layout I purposely loop the power bus because then the electricity has two routes (four actually if you count the track) to get to any point a locomotive might be on the track. On larger layouts there is often the need for multiple power blocks so the "large loop" often never happens. I think it would take a seriously large loop for the signal delay in the track vs in the bus to become an issue. There would be many other problems encountered before the loop got that big.

[stokesda]

I'm currently wiring my layout, and will be using DCC. I have read the wiringfordcc.com website repeatedly, but I still have a couple of questions:

1. My layout is a donut-style with a liftout bridge (actually a hinged drop bridge) allowing access to the center. I want to rig it with contact switches so that when the bridge is lowered, it will kill the power to the bridge and the approach tracks to keep any trains from falling 4 feet to their death. I've seen this done on DC layouts with lever-actuated SPST switches connected to one of the track wires. Question is for DCC, is it sufficient to have a single SPST switch attached to only one of the two track leads, or do I need one for each lead (or a double-pole switch)?

2. I have been told that it's bad to have your DCC bus wires in a continuous loop - that they should be broken up so the ends don't connect together. My question is that if you have more than one feeder per section of track, or if you have sections connected by metal rail joiners, it seems that there is a kind of loop right there, between the rails themselves, the bus wires, and the multiple feeders between the two. (I have a small layout and am planning on using only one booster and one "block"). Nothing I've read anywhere seems to say that I need to insulate the rails between every pair of feeder wires, but the whole "loop" thing just got me scratching my head. Can anyone shed some light on this? Is this a valid concern, or is it just my imagination?

Also, a small frustration... I think both of these questions could be answered if I could get my hands on a copy of the "Big Book of DCC," but it's currently out of print and unavailable from Digitrax until they come out with the new edition later this summer! I can't even find an old one anywhere (eBay, Amazon, etc.) for a decent price! Grrr!