I have seen posts in the past regarding sizing of buss wires in various designs. I have tried to search for these posts in order to size the wiring for my new, larger layout. The search proved fruitless. So, without further ado......
What is a good buss size for a 30 foot shelf layout? I am thinking #14 solid.
73
Bruce in the Peg
Bruce,
You are thinking, correctly!
Cheers,
Frank
If the power source is pretty much in the middle, that means a max one way run of 15 feet. #14 would be fine. I find stranded easier to pull under the layout since it flexes. Even if you are building on doors and turn the upside down to work on the wiring - stranded is just easier to work with to me - and I've done house wiring which is almost always solid.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Bruce, the easiest source of 14 ga. wire is NMD house wiring, but it's solid and has 2 conductors and a bare ground in it and would require stripping the jacket off. You could try Home Depot. They have a lot of different kinds of wire on their web site. I would also suggest trying Princess Auto. Go to their web site <www.princessauto.com> and enter "primary wire" into their search engine. It doesn't say if it's stranded or solid., I may be wrong, but I think that if it's called primary wire it's stranded. The prices seem reasonable. It's a great store to browse around in. My 11 year old grandson loves exploring the shelves. They've even got hobby tools, not model RR specific though. I believe there's an outlet near where you live.
..... Bob
Beam me up, Scotty, there's no intelligent life down here. (Captain Kirk)
I reject your reality and substitute my own. (Adam Savage)
Resistance is not futile--it is voltage divided by current.
I bought two 20' rolls of the 14 gauge white-sheathed household stuff with the bare copper ground included that Bob describes, Bruce. Two so that I could run about 20' in each direction away from my DB150. The trick to threading it through frame members is to remove the sheathing and the copper ground, and then all you have to do is run the two solid copper wires through 1/2" holes. The Klein mid-wire insulation displacing tool, also at Home Depot, isn't the cheapest tool you'll ever buy, but it's worth the $40.
If you elect to run the 14 gauge wires without removing the sheathing for any distance, do make sure your drilled holes are wide enough you don't break out in a sweat trying to yank that stuff through holes that are nice 'n tight...like I did.
-Crandell
Another vote for 14 gauge solid.
Rich
Alton Junction
Unless you have a lot of insulated rail joiners, the rail itself will serve as a bus, too, so 14 gauge is more than heavy enough.
Blind BruceI have seen posts in the past regarding sizing of buss wires in various designs. I have tried to search for these posts in order to size the wiring for my new, larger layout. The search proved fruitless.
Wiring on a Layout
Small Wire (28 - 40 ga.) Current Capacities
and i thought this chart, Resistance of Wire, was useful
i did a search for "wire current capacity"
greg - Philadelphia & Reading / Reading
Wire Sizes to Use in DCC
by Don Fiehmann
Length in Feet for a 1/2 Volt Drop
Highlighted area exceeds recommended current.
From a Digitrax Manual
6.3 Recommended wire sizes for power bus and track feeders
On an average size layout Digitrax recommends that the power bus from the
booster be at least 16AWG. When feeding areas up to 50’ from the booster, we
recommend using 12 AWG wire for the power bus.
From the main power bus, we recommend dropping feeders (22-24AWG)
approximately every 6 to 10 feet of track. Sets of feeders should be wired to
both rails and we recommend at least 2 sets of feeders per power district.
The wire gauges used (AWG) can be increased or decreased, depending on
your actual layout dimensions and operating power/current loads.
Lee
I have a doughnut layout with the command station at the midpoint feeding the bus in 2 directions off a terminal strip. Therefore, each bus is approximately 16' long. I used #16 stranded "primary" wire from Lowe's. The feeders are #22 solid. No problems.
Dante
Will you be using a DCC system on this layout? As others have mentioned, consult your DCC manual for recommendations on wire size and composition. I run a Digitrax system, and use 12 gauge solid conductor for the bus and 18 to 20 gauge solid conductor feeder wiring. The feeder wiring can be "thermostat" type (2 solid conductors with a jacket around the pair of insulated wires), or even just "hook-up" wire on a spool from Radio Shack. I use both with good performance results. Overkill is better than the other way around when it comes to wire size (less resistance in the wire). Lots of good advice on this thread.
Wilton.
I have two busses on my layout, RCOM (common rail for analog DC) and TCOM (common return for twin-coil switch machines.) Both are #12 solid, bought at Home Depot for, in my humble opinion, a pittance.
#12 might be overkill - but both busses are close to 80 feet long. Bear in mind that I'm still running open-frame motors and that the KTM twin-coils might have a momentary spike of 3 amps - each, with up to four in some diode-matrix installations.
As for dragging the wires through holes in the framework - i don't. I just tuck them into my steel stud, "C acts like L," girders and snap short sections of cap stock over them (and the rest of my wiring) to hold them in those natural wire runs. The few little screws that have been driven into the girders have been blunted by screwing pieces of erasers onto the exposed points. (Round screwheads don't count.)
When it comes to wiring, it's far better to be oversize than undersize.
Chuck (Modeling Central Japan in September, 1964 - with 1964 technology.)
When using the charts to figure voltage drop remember to use the actual bus length. That will be out and back length. So if your bus runs down 20 feet of layout. Figure voltage drop for 40 feet of wire.
Martin Myers
And also remember to consider amps as what's actually USED. Just because you have a 5 amp booster doesn't make 5 amps flow through the wire. If the most you ever run is 1 loco, then you woould never have even close to 5 amps at the end of the wire.
Randy,
A point well,spoken!
Hi,
My current layout was wired 3 years ago. Buss wires are 14 ga stranded. I chose stranded as it is more flexible (I have an around the room layout, two levels) and of course readily available in various colors for the different power districts. Of course you could easily use solid, its just a matter of personal taste.
IMO, more importantly is that you put in plenty of track feeders, every 4-6 feet on the mains and at least one on every siding, etc. For feeders, I much prefer solid wires, 22 ga. And of course, you want those small diameter feeders as short as you can, perhaps no more than 18 inches. After all, that is why buss wiring is done in the first place.
ENJOY !
Mobilman44
Living in southeast Texas, formerly modeling the "postwar" Santa Fe and Illinois Central
"Out and back?"
One needs a complete circuit for current to flow. So it's out the booster, along the bus, through the dedocder, and back along the other bus wire.
So if your furthest point is 20 feet from the booster, you have 40 feet of wire the current is flowing through.
rrinker One needs a complete circuit for current to flow. So it's out the booster, along the bus, through the dedocder, and back along the other bus wire. So if your furthest point is 20 feet from the booster, you have 40 feet of wire the current is flowing through. --Randy
True, but the voltage that is important is what the decoder/motor receives, is it not, so that is the distance "out": 20' in your example.
Dante,
A voltage drop on either side of a circuit has the same effect, it limits current flow. So Randy is correct when he said a 20 foot run is actually 40 feet. That is why both sides of a circuit have the same gauge wire. They are both equally important.
Jim
Also remember that DCC is AC. Both wires are supplying half the voltage. Return is through the other wire when it is not "on" Total voltage is the voltagew measured between the amplitude of each.
AC or DC has nothing to do with it. A load 20 physical feet fromt he source draws current rhtough a total of 40 feet of wire, 20 out and 20 back.
The loss is due to resistence in the wire - therefore, the actual voltage drop is proportionate to the current draw. This is why, despite the high resistence per foot of fine telephone wire, it is perfectly adequate to run Tortoise motors, since they only draw about 15ma. And when figuring for the DCC bus wire, just because you have a 5 amp booster doesn't mean 5 amps is flowing through the rie, if only 1 or 2 locos are running at the far end. The amp rating of a power source like a booster is the maximum that can be drawn from it - amps are not 'pushed' into a load, the load DRAWS a certain amount of current.
3-5% voltage drop is the most you would want. Here are a couple examples:
A 20ft distance (40ft actual) with a 5 amp load using 16ga will have a 6.8% drop which is too much. Using the same distance and load with 12ga wire, the value lowers to a 2.7 % drop which is much better. If you decrease the distance, the drops will go down, and an increase in distance will cause both examples to go up.
Keep in mind this is not the total voltage drop, the length and gauge of the feeders adds to this amount as does the number of rail joiners the feeders have to span. Also, the type and quality of the connections to the buss comes into play.
Little off on the calculations there. #16 is 4.0843 and change ohms per 1000 ft, 40 ft is .163372 ohms, Times 5 amps is a .81696V drop, 5.45% at the usual 15V for HO DCC. Borderline noticeable - you want less than 1/2 a volt. #14 in the same situation would be a .515V drop, good.
But again, this assumes a full 5 amps is being drawn at the furthest point along the bus - croded all your locos in the far corner again, silly dispatcher got everyone jammed up? More normal worst case is about half that, which means a .408V drop with #16, and a .26V drop with #14. Both well under noticeable speed change values.
Randy, I used a source value of 12v so we are both correct with our examples.