It's interesting that #14 has become the rule of thumb, but if you design the buss for a 12v system with a 5% max drop in the buss, it rarely is the size of choice. The table shows such systems for different buss lengths (1/2 the length of the benchwork) and different max Amps. BUSS DESIGN V system 12 Max V drop 0.720 Max I Max R Max L R / ft AWG 8 0.090 24 0.00375 12 6 0.120 24 0.00500 16 4 0.180 24 0.00750 18 3 0.240 24 0.01000 18 1.5 0.480 24 0.02000 22 8 0.090 20 0.00450 16 6 0.120 20 0.00600 16 4 0.180 20 0.00900 18 3 0.240 20 0.01200 20 1.5 0.480 20 0.02400 22 8 0.090 16 0.00563 16 6 0.120 16 0.00750 18 4 0.180 16 0.01125 20 3 0.240 16 0.01500 20 1.5 0.480 16 0.03000 24 8 0.090 12 0.00750 18 6 0.120 12 0.01000 18 4 0.180 12 0.01500 20 3 0.240 12 0.02000 22 1.5 0.480 12 0.04000 24 8 0.090 8 0.01125 20 6 0.120 8 0.01500 20 4 0.180 8 0.02250 22 3 0.240 8 0.03000 24 1.5 0.480 8 0.06000 26 8 0.090 4 0.02250 22 6 0.120 4 0.03000 24 4 0.180 4 0.04500 26 3 0.240 4 0.06000 26 1.5 0.480 4 0.12000 28 Note that for a layout on a 4 x 8 bench, with 3 amp max, #26 is an adequate buss wire size. On the other hand, a layout that's 48ft long, and has ab 8 amp max buss current, needs #12 wire. I think rules-of-thumb can be very misleading. By the way, the designs are done using the AWG copper wite table and Ohms Law. Copper Wire Table Gauge Ohms/ft Dia. 10 0.0009989 0.1019 12 0.0015880 0.0808 14 0.0040160 0.0641 16 0.0040160 0.0508 18 0.0063850 0.0403 20 0.0101500 0.0320 22 0.0161400 0.0254 24 0.0256700 0.0201 26 0.0408100 0.0159 28 0.0649000 0.0126 Sorry about the columns not ligning up.
I used 12 gauge solid for my bus system, and 20 gauge solid for feeders. When I was wiring a few years back, I went to Lowes and bought a 100-foot roll of seven-wire sprinkler wire, which is the 20 gauge solid. I just stripped the seven wires out of the outer insulation, splitting that with a box cutter. I got 700 feet in seven different colors. I can't remember what I paid, but it was a lot cheaper than buying single rolls--in fact, I think it was the same price as a single roll. I have noticed that sprinkler system components have skyrocketed in price the past few years, as I spent this weekend getting six drip zones and a regular zone (the veggie garden) back in top shape. I didn't need wire, so I didn't look at price for this year.
Basicly what he's saying is if you have a small layout you can use smaller Guage wire but when you have a larger layout you must use a larger Guage wire. In lower voltages the loss to length is alot differant than housing voltages like the power company's reason the higher the Voltage the lesser the loss to distance whitch= less amps =smaller wire. but don't forget that another factor to having voltage loss is not only the potental to melt the Buss and run like crap but it could also shorten the the life span of the Motor by overheating, It's not the fact that it won't work but more of a fact that it won't work right, like your house you could wire your rannge in 18Ga wire it would work (for about 10 seconds befor it melted to nothingness).
You can use solid wire wih no problem but if your running DCC you should run Stranded to reduce RF & Electromagnetic Interferance it's the way the wire is twisted kind of like Telephone wire Cat 3 Wire is like 4 revolutions per foot where Data wire Cat 5 is like 8 revolutions per foot.
Ray Stilwell wrote: "Note that for a layout on a 4 x 8 bench, with 3 amp max, #26 is an adequate buss wire size. On the other hand, a layout that's 48ft long, and has ab 8 amp max buss current, needs #12 wire. I think rules-of-thumb can be very misleading. Ray, thanks for taking the time to crunch the numbers. GM
a dozen poff's will make that 48 feet. Fact is, adding boosters when needed to NTRAK layouts will take care of any voltage drop problems. DB150- $150 PS515- $40 PM42- $64 PS12- $7 Thats over $260 per power district. This would purchase 850 feet of 12 ga zip cord ( I pay $160/500 ft. reel) BTW, the 12 ga low voltage lighting cable available at Home Depot is the best deal going and the insulation is heavier. It's stocked in 14ga. as well. Reduce the voltage drop, use less equipment. Not always necessary, but large NTRAK layouts are becoming more frequent. At the 2004 convention in Chantilly, the plan worked with exixting wiring standards. There were over 100 amps of boosters hooked up to that layout to make it work properly. I have yet to see any evidence that heavier wire will cause trouble. Martin Myers BANTRAK
Well maybe I did not state the question correctly. Here is the situation. [Remember I am electrically challenged by anyuthing beyond white wire and black wire] We [the club] run straight DC. We have no intention of going to DCC. Our modules currently have the CJ plug with their stated inherent voltage drop along with 16 gauge lamp cord used as a main buss. We operate one train per track using Aristo radio throttles. We typically set up a rectangular layout that measures 14 X 22 or 18 X 26. Do I need to go heavier than 16 guage wire. Heck, I ran an electric lawnmower using a 100 foot extension cord made of 16 gauge wire.
You can try 16 gauge wire for your module. If you experience problems, you can change it out for 14 gauge wire. Stay cool and run steam.....
For my Z layout, I'm planning on 30ga feeders,a nd 14-16ga bus wires. Longest run will be about 4 feet for the bus, and a few inches for each feeder. In my last N layout, 12 ga wire bus, 20ga feeders every piece of track longer than 5". Had NO problems with voltage drop, but boy did the soldering get old! Next layout may get a bigger bus, since it will go further distance. Maybe 10ga.
Yes, if you can tell me what you don't understand. The one chart shows the required wire size for keeping the voltage loss at the end of the buss at or below 5%. It is shown for a 12 volt system in all cases. I The first column is the expected max current in the buss. The second column is the max allowable buss resistance at that current. The third column is the length of the buss. The fourth column is the maximum allowable resistance per foot of buss. The last column is the required minimum wire guage. The wire table simply lists the resistance per foot and the diameter of AWG copper wire for sizes of interest. If you know the length of wire, multiply to get the total resistance. Then if you know the current, multiply to get the voltage drop. If it's under 5% of the operating voltage, you have a workable buss. But the table goes farther an shows you the best wire size to use for a given buss length and current load in a 12v system. I note that someone posted that one should use stranded wire instead of solid to reduce RF interference. Not so, mon amie. The strands in a wire will do nothing for RF. It's the twists between two conductors that do the trick. So, one can use solid wire with the same results as stranded as long as the two solid wires, or the two stranded wires, are twisted as they go along the benchwork. I also note that someone else is worried about melting the buss, etc. Note that if you design to keep the voltage drop at or below 5% of 12 volts which is 0.6 volts. Multiplying this voltage drop times the buss current gives the watts dissipated in the buss. So, even with an 8 amp buss, the watts dissipated will not exceed 0.6 x 8 = 4.8 watts which will be spread along the buss. This is less than a Christmas candle bulb, but spread over many feet. I doubt that you could even feel the heat it produces. There simply is no way the buss can be a danger assuming adequate circuit breakers are used to prevent overloads from shorts, etc. The whole idea is boogyman to scare the uninitiated.
I don't worry about any of the above. I used 14 gauge solid copper wires for bus lines and 22 gauge wires for feeders dropped from each track section and the JJJ&E which is a Unitrack layout has been fully operational for over 6 plus years. There are no drops in voltage and I can run the system for hours without any electrical problems. I'm also using DCC on the layout. Sometimes, the less complicated the electrical issues, the better off you are. Stay cool and run steam.....
Posted by Ray Stilwell: "I note that someone posted that one should use stranded wire instead of solid to reduce RF interference. Not so, mon amie. The strands in a wire will do nothing for RF. It's the twists between two conductors that do the trick." Part of this is correct and part incorrect. Stranded wire is used for its flexibility and at higher frequencies(RF) to reduce skin effect. This is where most of the current is carried on the very outside of the wire and thus for a given wire size reduces current carrying capacity. Not a problem in model railroading. AL
Here is more than you ever wanted to know about wiring your layout: What you want to avoid is voltage drop. Voltage drop makes your loco both run slower and pull more current than it should. The relation between wire and voltage drop is that voltage drop is greater with greater resistance AND with greater current. Let's take resistance first: The total resistance to current flow depends on two things: the diameter of the wire and the length of the wire. Larger diameter wire has less resistance. Wire resistance is measured in ohms per length so for any wire size, the total resistance increases as the length increases. From a practical standpoint this means that long runs of wire should be a large diameter. Short runs of wire from the main feeder to the track add relatively little total resistance. Also, the greater the current, the more voltage drop so if you are pulling a lot of current, you get more drop. For example, if you are supplying 2 motors, you drop about twice the voltage for a given length & size of wire as if you are supplying one motor. To make matters worse, the current tends to go up as the voltage drops. The amount of drop actually depends on loco speed, number of cars being pulled, etc., but ideally you would like to have only half as much wire resistance when running 2 locos as when running one. From a practical standpoint, #14 is a good size to run as the main feeder. This wire is big enough to have pretty low resistance even on long runs. The stuff you buy at Lowe's (Home Depot, hardware store) is rated for 15 amps current at 120 VAC so it is plenty big enough for a model railroad. I use #22 for feeders and that should be okay for short feeders between the #14 wire and the track. If you have any doubts, use #18. Another thing that is practical for short runs is to run two smaller wires to the same point because half of the current goes down each wire so assuming the same wire sizes, the total resistance of two wires is half the resistance of a single wire. You can use either stranded or solid wire for feeders. There is no advantage to solid wire. Stranded wire is easier to work with. Resistance / voltage drop are the main concerns. Overheating is not of much concern on model railroads unless the wire is VERY small and / or there is a short circuit and the power supply is unprotected against over current. No UL listed commercially manufacturered power supply will be unprotected. At least as important as wire wize and type is that the connection between the two wires be good. You can easily have more resistance in a bad connection than in all the wire on the layout. I wrap the feeder wire around the main wire several times and then solder it. If you don't solder it, use a commercial connector. Ray
Thanks Bob In fact I do run mostly steam. But not N gauge. I was just lurking over here with the N stuff. I model in HO. Ray
