Out and back is the distance out one wire and back through the other wire to complete the circuit. You should be fine at 30 - 40 feet with 14 gauge bus wire. You can leave the bus in a loop or cut it. The lengths mentioned are not long enough to worry about signal crashes. Same goes for twisting. Twisting is good but not really necessary until you get bus runs of 35 feet or more.
As already posted, check your layout by shorting the track at various places out to the furthest distance from the booster. The booster's short circuit protection should trip immediately when the rails are shorted. If it doesn't, add feeders in that area or increase bus size. If the short circuit tests work OK, your wiring and DCC system is good to go.
Martin Myers
I plan on running 4 MTH fully equipped locomotives at the most at any one time. All of my accessories are supplied seperately from track power by old DC transformers. I realize I might get close to the the 3-5 amp power supplied by the MRC Prodigy Advance 2 module. If I add passenger cars with lighting effects, as I plan on doing. Then I guess I'll look into wiring in another booster/zone by dividing my layout in half. Right now I'm really just concerned on adding the MRC DCC system to my new track plan. My new track plan is just a bare bones long loop with a siding or two, utilizing all of the bench work around my basement train room. My final plan will be way more detailed with double main, large yard, roundhouse, sidings, etc. I just wanted to get a main line down covering my real estate before the holidays. Allowing me to showcase my trains and visualize what's possible for the future, and get more familiar with MRC DCC by using it. But of course I wanted this simple, yet large, test set-up to be wired to run as flawlessly as possible. For the sole reason of building this plan is too enjoy running trains using DCC and becoming more familiar with it. Before expanding into full DCC capabilies: power districts, DCC turnouts and accessories, computer controlled, etc. Thanks again, and will still take any and all suggestons.
Thank you all for your replies and answers! I'll be adding my Prodigy Advance module tomorrow. T-ing off from the module in either direction by cutting my bus wire at the farthest mid point from the module. I might still lightly twist my bus lines around each other before I attach my feeders using IDC's. All of my feeders are in place now just not connected yet to the bus lines. I figure it'll be impossible to twist them after connecting the feeders w/o undoing them all. Just figure doing it a little to err on the side of caution. I've read several places where interference can come into effect on long runs, and twisting the lines can be an easy fix. I cant wait to finish these last connections. So that I can finally stretch out my engines legs on longer track, and just in time for the holidays.
My knowledge is with digitrax but i imagine that most of the systems are similar. 14 awg is ok for the length of your buss run. My clubs buss is a mishmosh of 18 gauge wire and 22 gauge rail feeders. I am upgrading it to 14 gauge buss with 20 gauge feeders. most of the DCC manufacturers recommend not making a loop with the buss. I take that to mean you must also not connect your track in a loop without using insulated joiners. My clubs buss run is almost 100ft without any problems due to voltage drop or signal loss. Actually we have four buss runs parallel with each other to make four power districts protected by a digitrax pm42. We did upgrade from a 5 amp system to an 8 amp because we were running so many loco's with sound that the command station was shuting down as we got close to the units maximum output.
The thicker your bus wire, the longer you can run it out from your power supply and still have good quality DCC signal imposed on the voltage. If you make twin T's, with two wires running from the output terminals on your base controller in either direction, you will be in the best position to maintain signal integrity, regardless of the length. So, as Phoebe Vet suggests, centralize your base station to the extent practicable, and have two sets of bus wires, positive and negative, going off to each side down the length of your benchwork. No need to loop it back. All you need to do is to keep it neatly tucked out of contact with grounded objects and with each other.
It couldn't hurt to wind the two wires after maybe 25-30 feet, but I don't think it is strictly necessary. Fifty feet, yeah, probably.
-Crandell
Run your buss around the layout and put the command station in the middle of it, not at one end.
Whether or not you need a booster is a function of how many engines, lighted cars, and accessories are drawing power, not the length of the layout.
Once you have the track wired, test the short circuit protection at the point farthest from the command station. Many guys drop a quarter across the rails. I usually use a screw driver. It should trip the breaker in the command station. If it does, you are in business.
Dave
Lackawanna Route of the Phoebe Snow
My layout is essentially a stretched out (loop) dog-bone running along my basements perimeter walls. I plan on using Prodigy Advance 2 as my control that runs at I believe runs 5 amps or less. My bus wiring is 14 guage with 18 guage feeders mirroring my main line under my benchwork. My mainline runs nearly 70 - 85 ft loop where I'll be connecting the MRC command module/built in booster. My questions are these: I've heard it's bad to have the busline run as a loop back to the booster? If so, I plan on cutting the loop at the farthest distance from the module. In essence making two 30-40ft bus runs from the MRC module/booster. I've also heard not to exceed 30ft on bus lines of 14 guage. So is this right? Do I need to look into buying another booster for my layouts size? Is it ok to just cut the loop, for do the bus lines need to run back to the module? I've heard that you need to double your wire figures for "out" and "back"? I thought DCC wire runs just need to run out....am I wrong? If I do cut the bus lines, I'll be left with an "A" and "B" bus line essentially running 35ft and terminating....will I foresee command problems near the end of these lines from the 5 amp module that coms with the MRC Advance 2? I hope this makes sense. I do plan on twisting my bus lines a little to cut down on interference on long runs..I read. Any help at all will be grealty appreciated!