I'm starting the wire planning for my new layout. (Last of the roadbed should be down soon.) Can someone clarify a few points on bus length and connectivity?
I've read all sorts of things on the forums and other internet resources and am comfortable with max lengths and wire gauge needed but these two concepts seem to escape me:
1. For an easy example, say I have a layout that is 50 feet long along one wall. And I put my command station / booster right in the middle. So 25' from each end. If I run a bus to the left and the right, do I have a 50' bus or two 25'? Said another way, is the bus length calculated as distance from the booster or in total?2. How do I run multiple buses from the command station / booster that only has a Rail A and a Rail B connector slot? Do I simply run one set of wires from these slots all the way to the left and and then my second bus is spliced into the first using a connector of choice (solder, suitcase, etc.) and then runs to the right?
Thanks in advance.
EarlyNinetiesCR2. How do I run multiple buses from the command station / booster that only has a Rail A and a Rail B connector slot? Do I simply run one set of wires from these slots all the way to the left and and then my second bus is spliced into the first using a connector of choice (solder, suitcase, etc.) and then runs to the right?
My bus wires are as you describe. I ran two wires from the command station to a junction block / terminal block with screw connectors, from there I ran three pairs of bus wires to where i needed them.
Hope this helps.
The length from the command station is based on the thickness of the bus wire. For example, the charts I've referenced show that 14 AWG (aka 15 amp house wire) can run about 40 feet with a minimal drop in voltage. Some show 50 feet.
So it depends on the thickness how long your runs can be. If you use 12 AWG, you get a longer run.
Rio Grande. The Action Road - Focus 1977-1983
riogrande5761The length from the command station is based on the thickness of the bus wire.
I would phrase it the other way around. The gauge you should use is based on length of the bus.
25' left and 25' right is 25' of resistance and voltage drop. 50' one way is 50' of resistance. I would use a terminal strip because there would be at least one more sub bus running to a DCC reverser. If it's a 50' switching layout, there is no reason why you couldn't solder in a t shaped bus.
Henry
COB Potomac & Northern
Shenandoah Valley
EarlyNinetiesCR1. For an easy example, say I have a layout that is 50 feet long along one wall. And I put my command station / booster right in the middle. So 25' from each end. If I run a bus to the left and the right, do I have a 50' bus or two 25'? Said another way, is the bus length calculated as distance from the booster or in total?
In your example, you have what I would call a split bus (there may be an official terminology), with a short piece (say 6") to a "Y" (split) and the two extensions 25' to each side.
Voltage drop only occurs between the booster and the "load" (running locos), due to the current running through that section to the locos. The goal is to hold voltage drop to no more than about 1/2 volt. The voltage drop is proportional to the distance from the booster to the load (the locos) as well as the current draw. If there are locos all the way at the left and they are drawing nearly the booster output rating, that would be the max voltage drop (to that point). If the locos are half way to the left, you will have 1/2 that drop, as the current is travelling through less resistance (1/2 the left side bus length). In both those situations, there will be no voltage drop anywhere on the right length, as there is no current to the track with no load.
I suggest that you split the booster output near the booster, making a "Y" for the two outgoing legs. I used suitcase connectors for the many track feeders connected to the bus (a debatable subject) but would solder this ultra-important connection. Or you could run a short wire to a barrier strip where screws secure the wires.
Check what AWG size wire will go into your booster output On my NCE 5A system, IIRC I could not even get my 16 AWG bus wire to go into the output thingy. I was using stranded wire and just removed a few strands so it fit. Someone might suggest a better way, but tell us if you need help on that and an expert can weigh in if you provide details.
Paul
Modeling HO with a transition era UP bent
Regardless if you split the output and run two lines, one in each direction, or run one long 50' bus but tap into the middle to connect the booster, it's electrically the same. You have a maximum bus length of 25 feet since that is the longest distance from the booster to the furthest piece of track. Mechanically that may be a long 50 foot run of wire, but since the power source is in the middle, electrically it is 25 feet.
==========<booster>==========
=========||========= || booster If it stays formatted properly --Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
I haven't seen anyone yet mention circuit breakers for your power bus, or setting up the individual legs of your bus as separate power districts. If you run the command station output immediately to nearby breakers, you can then take track power from each breaker anywhere you want it. Each leg will function as a separate power district for you. The breakers will, aside from protecting your layout and equipment, provide the physical split you need in your wiring.
Specifically, if I were going to build a t-shaped power bus, I'd run every individual leg of the bus through its own breaker (unless one 'leg' was such a shortie that it would never call for much amperage; then I might wire two legs as one district through one breaker). The benefit of using breakers to do that is because, especially with a layout built to the shape you describe, if there's a short at one end of one leg, without breakers that short will take the whole layout down. With breakers, a short on one leg will only take down that leg, leaving the rest of the layout up and running. It would make locating a short MUCH less difficult, since you would know that the short is confined only to the leg that went down.
In case you don't know:
There are a variety of breakers available, many very low cost. Some are set to a specific amperage, and on some you can adjust the amperage at which the breaker will trip. Some use what amounts to a fuse, which burns out on a short and requires replacement to bring track power back up. Others have circuitry that resets when the short is cleared, not requiring anything like fuse replacement. I Use PSX breakers, which are the auto-reset type, partly because I got a great sale price on the 4-ganged PSX (4 breakers on one board; you can snap off one or more breakers for use elsewhere) and partly because you can use the PSX-AR version to also create a breaker-protected auto-reversing loop without anything else needed (no fancy wiring, etc.).
One thing often misunderstood about breakers is this: I have a 10-amp NCE command station, which splits into four power districts. The breaker for each district is set to trip at 3 amps. (I run multiple sound decoders and other things in each district.) 4 districts times 3 amps each is 12 amps, more than my command station output. That's not a problem, though, because I rarely run enough stuff on any district that even approaches 2 amps total.
Hope this is useful info. Have fun!