Telephone Wire?

Please do not laugh me off frisco.org if the answer is no. (Not that I really think anyone would.)

The current drops in some places around my DC layout. I believe I need to wire the layout to get consistent current. I have an abundant spool of leftover telephone wire. Could I use telephone wire to wire the layout? I'm expecting the answer to be "no" but I wanted to ask before I purchase wire. If the answer is no, what gauge of electrical wire do I need?

 

Honest question. No, you cannot use telephone wire. It will not handle the voltage or the amperage, and you will cause a fire! Telephone wire is not meant to handle those loads as the signal is not energized and is extremely low. Get yourself good quality wire. The lower the guage number, the more amperage it can handle, but the resistance increases. 20 gauge is more than adequate. Any smaller (24, 26, 28...) and you run the risk of the telephone wire. Any higher (18, 16, 14, 12...) and the gauge will impede your signal through resistance.

 

Jim and All:

When in doubt on questions of this nature, I always go here first. Some refer to it as "the Bible" for DCC wiring issues.

http://www.wiringfordcc.com/

 

My first thought was, "What kind of telephone wire"? The newer stuff, or the old type which is 20-22 gauge?
I wired a lot of layouts with the old stuff. Never had any problems.

 

Yeah Jim. Your 22 gauge is fine. It's not like you are running DCC, motorized switch machines up the ying-yang, lights, signals, etc.

 

First the disclaimer, I am no electrician, however, Keith Robinson can vouch for my layout wiring and I stayed at a Holiday Inn Express last night.

The feeders or drops on my layout are single pair, stranded 22 ga (I believe), copper telephone wire attached to every piece of track (no matter the length). They typically don't exceed 18" in length, so they are fairly short runs. The feeders are soldered to a stranded 12 ga bus that circumnavigates my layout. The voltage on my Digitrax system is 12.6v and my blocks are set up in 5 amp sections.

My DCC layout is laced with motorized switch machines (switch machines run on a separate 12v DC circuit but use the same 22 ga wire) and has been functioning well for 10 years with no fires. My previous non DCC (14v) layout operated for 12 years with the same standards and, again, no fires. All I have had is reliable electrical operation. No signal problems, no downtime (except for a pesky short a few months ago) no dissatisfied operators.

Fortunately, I had good friends like Keith and Joe Kasper (GE Medical Systems Technician) to watch over me as I wired the layout.

 

I just couldn't resist getting into the telephone wire issue as I am using it on my EasyDCC system to control my turnouts using the company's AD4 accessory decoders. The AD4's are actually cards inserted into a 44 pin edge connector and each controls 4 turnouts. I can also set up macros in the system to set up and control routes. The power to the rack of edge connectors is 16 gauge wire connected to a separate buss and booster than the track and then two of the wires from the card are connected via the phone wire (bundled on lower right corner) to edge connectors on the other end plugged into the tortoise switch machines. Some of the runs are as long as 15 ft. Credit goes to my friend Bob Wintle who spent several hours wiring and setting up 15 switches to control my Neodesha yard. By the way did I mention that he spent many years as the Electronic Technician in a bomb factory so he of all people should know how to wire something to avoid starting a fire!

 

Geez, #12 wire? How many amps at what voltage are you trying to pull? I use a 50' #12 extension cord to power my table saw!

I looked at the DCC info link and it seems quite over engineered to me. #22 wire lists a 0.03 ohm resistance and a 0.128 voltage drop. What length was the wire? The length of the run makes a huge difference. So, instead of getting 12 volts to the track, you are going to worry about only getting 11.87 volts? Is it THAT critical? As far as the resistance, 0.03 ohms is less that negligible. Again, the DCC wiring "bible" was obviously not written by an electrical engineer. And if it was, he left out a LOT of important info

I figure if Maw Bell and AT&T can run 24v and 5 amps over telephone wire for 75 years, it ought to be able to handle 12v at 2 or 3 amps for a few hours without burning down the house.

 

I know that Bob Wintle.

 

Going to have to quit using 24 ga for my electric oven then . . .

 

Hi Fred.

As I said in my disclaimer, I am no electrician. My electrically inclined friends told me to use 12 ga stranded. I may cover more distance than the average layout builder, anywhere from 25' to 100'. Not sure how your formula works but I am thinking there may be some attenuation with those distances. One thing I do know is that 12 ga is expensive these days.

One more thing, I run sound and my buds tell me that one sound engine can pull 1 amp all by itself.

 

Brandon and All:

It is ironic that this very subject comes up now because in the March 2012 issue of Model Railroader Magazine the monthly segment of their new project railroad covers track laying and wiring. The layout, entitled Virginian just happens to be 4x8 ft. Editor David Popp closely follows a technique first covered by Andy Sperandeo in the Model Railroader Special Edition series “How to Build Realistic Reliable Track”. Andy’s article was entitled ”Bulletproof Track Wiring” and here is the method in a nutshell. Both use short lengths of 22 AWG solid wire for the track feeders which on the Virginian project are connected to a 16 AWG buss using 3M brand insulation­­-displacement (suitcase) connectors. In Andy’s article he strings the 22 AWG barely under the layout where he connects them to a secondary 18 AWG stranded wire that then connects to a 12 AWG buss wire. Both connections are made using the 3M suitcase connectors referenced above. He tries to keep the 18 AWG portion to no more than 12 inches long.

In comparison all of the wiring on my layout incorporates 20 AWG stranded feeders soldered to a 12 AWG stranded buss with connections to every piece of track. It was done by my good friends from Kansas City (Rick McClellan & Keith Robinson) and as Rick pointed out, that is how they do it up there.

Two very different approaches that I’m sure both work. I use Code 83 Atlas track and yes the feeders are visible but I don’t expect that to be the case when I get the track painted and weathered. By the pictures in the magazines, especially the ones in Andy’s article, you can hardly see the feeders as they look like spikes.

 

That sounds reasonable.

If you go to this web page: http://www.rowand.net/Shop/Tech/WireCapacityChart.htm
you will find a chart that shows the capacity of various guages of wire. 20AWG can handle 8 amps over a short run at 12 volts. 12AWG is rated at 60 amps with 12 volts. That is a LOT of power! If you are running a mega layout at a mall somewhere or running 100' of track, yeah, 12 AWG would be appropriate. But a 4x8 board could run on telephone wire all day long and never even get warm.

But it is going to take a very large, complex layout to require 12AWG wire. Besides, like he said, it isn't cheap anymore and it isn't very easy to work with on small layouts.

I know I'm a newby here and I'm not trying to ruffle feathers but I have found by experience that simple problems require simple answers. Over engineering things does not make them better, just more complex.

 

I am a retired Electrical/Electronics Engineer with close to 50 years experience. I am also a Master Electrician, and a computer A+ certified Technician. The National Electrical Code states that 18 Gauge wire is rated for 7 Amps at 600 Volts AC, 16 Gauge is rated at 10 Amps, 14 Gauge is rated at 15 Amps, 12 Gauge is rated at 20 Amps, and 10 Gauge is rated at 30 Amps; those are the ampereage rating that these wires can be fused at, BUT, the NEC further states that no wire can be run continuously at any more than 80% of that rating. Therefore 12 Gage wire for even a large layout is probably overkill. Why not take a moment and calculate the wire size you need? Google for a table of wire resistance per foot. Decide what voltage drop you can live with and use that as YOUR standard, screw everybody else( Rule 1). Now use the wire resistance from the table times twice the wire length( a 100 foot run is actually 200 feet because the current has to go out and back from the power source). Multiply the total wire resistance times your maximum current rating you want to carry in that wire and you will get the voltage drop for that wire run. Is that value more than your voltage drop standard, if so go to the next higher wire size, smaller number, and try again until you find the wire gauge for your layout. No need to use anything larger than that gauge. Track drops are so short that you can use just about anything you want, why; because you are very unlikely to draw maximum current on any track section ever. This comes under the same idea of those people that say always use a 1000 ohm resistor with all LEDs, just aint so!

 

As the discussion reveals, "it all depends" is the correct answer. Both extremes have been answered. On Rick's layout the Springfield power block could have three sound units on a single piece of flex track, two more on another, two yard switchers moving around, etc. Jim's Zalma Branch will rarely have two locos on it at the same time.
It's great to have friendly folks who can provide good info to the less technical of us. We all need to remember to provide a little more background when we are asking questions (time period, scale, etc.)