I am presently running 14 gauge bus lines for my 15 x 22’ or so shelf layout. The feeders are 20 gauge every four feet. It is my understanding that bus lines should not exceed 30’. Is it ok to split the bus lines so you have 30 of bus going in each of two directions (ie 30 feet to the left of the control panel and 30 feet to the right? Also, I only have half of the layout is completed. Should I run bus lines for the entire layout now as one long section or splice in the second section of bus line when the track laying is completed? I would like to do it right the first time.
In short, 30 feet of 14 gauge bus wire is probably okay, but I would not go any longer of a run with 14 gauge. In fact, were I in your shoes, I would go 12 gauge just to be sure.
Splitting the wire with the DCC system booster in the middle is a very good idea since it keeps your run down to 30 feet in any direction (as opposed to 60 feet if the system was on one end of the run).
Splicing the bus wire is also okay as long as the splice is a good soldered connection. However, for a layout of the size you give, you should consider several boosters, each with their own power bus to make short management and wiring debugging easier. Each booster would have its own power bus wires that feed that section of the layout.
My referenced Forum Clinic above discusses these issues in more detail.
Joe has it right…It’s the right way to do it.But,i have a similar situation with 40 ft on either side of my power supply and have been running that way for at least 10 years with no problems.I used the 14g wire because it was much easier to work with.I plan on someday adding boosters and splitting the layout into 4 or 5 sections, as some time it takes a bit to find what shorted where and shut down the layout.Also, with 10 sound equiped loco and many lighted cars it some times takes a few tries to re-start.
It also depends on how many locos you are running. The numbers often quoted for the size of the bus wire are usually built around having a minimal (less than half a volt) drop with a full 5 amps flowing through the bus. But if you only run a single loco drawing .5 amps, that’s 1/10th the voltage drop. So say a 40 foot run of #14 drops 1 volt at 5 amps (just making up numbers here, there are many sites with resistance per foot tables for various wire sizes, and then you use Ohm’s Law to calculate the voltage drop: V=IxR where I is the current and R is the total resistance for the wire run (remember if it’s 40’ long, that’s 80 total feet of wire - you need the complete circuit!). Anyway, say at 5 amps your run drops 1 volt. But you only run a single .5 amp loco ever, so what you actually get is 0.1 volt drop - not even noticeable! Even if you run 3 such locos, total 1.5 amps - that’s a 0.3 volt drop - still not likely to be noticed. This is why everythign seems to work ok even though your wire is smaller than the ‘experts’ say you need. But if in the future you load it down to the full rating of the booster, then you will have a noticeable voltage drop.
This is also why you don’t need to figure out some way to attach a #12 wire to the frog of a turnout - and why the Tortoise contacts can handle switching frog power - only 1 loco can occupy the frog at any given time (and be on the rails, anyway!). And it’s why short runs of smaller wire used for feeders aren’t an issue - over a sort distance the drop is neglibie, and it’s also not likey that you’d be drawing the full booster current through one small stretch of track.
DCC bus size has been a hot topic over the past several years. Basic model railroad wiring for years has been somewhat ‘marginal’ - even on great layouts. With DCC and the higher currents flowing, the track does not make a real good ‘bus’. I have a good size layout(25’ by 20’ area) and use #18 wire for the ‘bus’, with #22 wire for the 6" from a solder connection on the rail to a connection on the bus via a 3M ‘suitcase’ connection. I have these feeders on every section of rail and no bus is over 25’ long, from the booster power supply. I have used one of those RRampMeter devices to measure the voltage and I have maybe a .6v drop at the far ends of the trackage(going through the Terminal strips/PM42/#18 bus/#22 feeder/code 100 N/S rail. As others have mentioned, well designed wiring, with good connectors will pay dividends later when you run your railroad. Basic track/wiring points:
o - Do NOT trust rail joiners for electrical pickup
o - Drop a feeder from every section of rail
o - Learn to solder(those pre-soldered rail joiner/feeders still require the rail joiner to
have a good ‘mechanical’ contact) - Something they cannot provide.
o - Divide you layout into ‘power districts’. You do not need fancy devices - Joe Fugate’s
1156 auto lamps are a good way to do this.
First, let me say Thank you to everyone who responded. There is a wealth of knowledge to draw from using this forum.
Secondly, I will only have two or possibly three locos running at any given time and they will be BLI SW8’s or Geeps so I don’t think I will be over taxing the amperage output of the Power Cab. Probably the 12 gauge wire is a good way to go since I have yet to solder the feeders to the bus. I would like to run the bus lines through out the entire layout and then “T” into them where the primary cab connection will be. I will definitely be using a booster or two.
Lastly, is there a tool that would allow you to easily strip the insulation from a center section of bus line? I can’t think of any other way to do this other than cutting through the insulation in two places and then splitting it down the length between the two cuts?
I would use suit case connectors, but have heard mixed reviews concerning their long term usage.
Electrical supply store or home depot will have a wire stripper that looks like pliers but works on a cam action that will be perfect to strip wire in the middle of a run.I’m not sure about the price,but I think it’s about $12
I’m confused about something. Maybe someone has an answer…
I called NCE, and was told that the DCC waveform is basically square-wave AC.
Now I’m a nuts-and-bolts engineer, not an electron-pusher. Why does DCC voltage drop by the amounts we’re being told if it’s alternating current? In house wiring we’re sure not limited to short runs from the panel to a light before the light gets dim from voltage drop. I talked with some of my avionics folks here at the aircraft plant, and they told me that even high-frequency alternating current does not have the sort of voltage drop over a given run of wire that DC does…
I don’t have the technical knowledge to answer you definitively.
But I can tell you, subjectively, that I consider much of the ruckus over this issue to be overkill for those of us who don’t run large club-sized layouts and host large op sessions. I understand the ‘better safe than sorry’ mindset. But at the same time, when you dig into it you often find the rationale behind all this is “well… if you ever wanted to run 17 sound equipped locos simultaneously all pulling lighted cars…” Some folks do exactly that, maybe more… For them, yes, maybe a little obsession with this is necessary. But we’re all smart folks, so far as I can tell, and I think a little more ‘scalability’ of the recommendations is often in order.
In my experience you are correct - the AC current/signal travels much further, much better than the ‘conventional wisdom’ credits it for.
I ran my first DCC layout with over 200’ of mainline track off one set of 20-ga. feeders for years. While building my current layout, I recently hooked up the first 120’ circuit of track the same way and ran with no problems… Which basically means to reach the furthest portion, the currnet/signal carried through 3’ of 20-ga wire, then through 60’ of track from there.
Now, I have no intention of running the layout that way for real. I’m running a bus and dropping feeders. But I also don’t get overly worried if I have (gasp!) more than 6 feet between feeders, or if my bus goes 34’ instead of chopping it off right at 30’… etc.
When talking about voltage drop in DCC, the AC or DC nature of the signal isn’t the issue. There are a few things about DCC that make this a bit more important to consider than with a block control system.
One is that in DCC there is a signal along for the ride (or actually, giving the power a ride). So, even small interruptions or glitches in the power to a locomotive can potentially be detrimental to operation. With DC, you’d probably coast right through and never know there was anything there.
Then, and this is where the bus size and voltage drop are issues, there is the fact that that single bus is providing the power for all of the locomotives in that power district. In a block control system each block is its own bus, so the most current you will draw through the wires is enough to power your largest consist. In DCC you might have three or four times that current requirement. From there, Ohm’s law takes over, whether we are talking AC or DC. The wire has resistance, there is current going through the wire, so there is voltage loss. Ot a certain point, the decoders won’t decode. In DC you’d just turn up the juice. In DCC, you are done.
All of that said, there is probably some overdesign in the usual recommendations. The track itself can be helping a lot, and make a hefty bus seem excessive. But the safe thing to do is to assume that there will be a bad rail joiner, a small gap, or some other reason that the track isn’t doing what you think. So the safe thing to do is run the bus a bit bigger than you might, and drop more feeders. I did some of the calculation once, and the 30 foot bus length (each way from the source) with #14 wire was reasonable. This was figuring on a reasonable sized consist (four or so, I think) at the end of the bus, and left a little room for slop. Also, the current draw can vary a lot from loco to loco, so it is all just a guess, anyway.
The tool I have is made by Ideal and I got it at Home Depot. It is a heavy, all-metal tool with blue handles. It sort of has a double jaw, one side is a clamp and the other has a die with different holes for varius size wires. When you squeeze the handle, first the clamp closes and then the jaws seperate allowing the die part to strip the wire. This works equally well in the middle of the wire or at the end. It’s also the single best electrical related tool I ever bought - considering that besides my layout I’ve had to replace nearly all the AC outlets in my house, and I always cut back the wires to get a fresh end for the new outlet.
The other issue for model railroad wiring that has been given very short shrift in the past is “almost short circuit” currents. Folks in 3 rail O with its big current draws and power supplies are beginning to understand the situation where it can be a real issue.
This problem crops up when under-size wiring has just enough voltage drop at short-circuit loads to prevent the circuit breaker/fuse/circuit protector from tripping. If you have a 10 amp power supply with enough 20 gauge wire in the path, when the short circuit at the track occurs, the breaker may never trip. In this case, the wire will get really hot, though - capable of starting fires.
The above is why household electrical code mandates 14 gauge wire for 15 amp circuits and 12 gauge for 20 amp circuits. 18 gauge wire maxes out at 7 amps, and 16 gauge at 10 amps. Current rating drops about in half for every 2 wire sizes down. This also illustrates why power districts are a good thing, as are current limiters (Joe Fugate’s light bulbs).
In most DCC cases, the current limits of the power supply and voltage drop issues prevent currents from approaching the wire limits, but it’s something to keep in mind.
Well, let me just say that on my layout, I have my 14 AWG buss running from one end to the other of my mainline, which is 200’ long. My Digitrax Zephyr is connected at one end, putting about 180’ of wire to one side, and 20’ to the other. I dropped 20 and 22 AWG feeders every 9’ or so. Every week, I operate my layout with three people, using at least 3 or 4 engines at all times.
At no time have I ever had a problem with voltage drop, losing signal, etc. I have far more derailments than electrical problems (mainly because some of my layout is 50 years old).