# Gauge of power wire



## philly33 (Apr 17, 2010)

Just starting to build road bed so I'm a ways off but what wire would be recommended to pull through a subterranean pipe to provide track and accessory power?


----------



## Russell Miller (Jan 3, 2008)

Use the wire made for low voltage lighting. I used 10 gauge because it was on sale at Home Depot but 12 gauge is usually enough.


----------



## Greg Elmassian (Jan 3, 2008)

I use 10 gauge, but I run trains that draw up to 10 amps. I use conduit also, and that allows me to buy a lot less expensive wire, the wire that houses are wired with, thin jacketed. This also will give you more room in the conduit. 

The low voltage wire has a lot thicker insulation, since it's made for burial in the ground, and to withstand some "gardening". 

While stranded is easier to deal with, solid wire resists corrosion better where it is exposed. 

Regards, Greg


----------



## Tahoe1 (Nov 10, 2008)

Building wire with insulation like THHN or THWN :

#12 AWG is usually good for a 20AMP circuit

# 14 AWG " " " " 15AMP Circuit.


----------



## Greg Elmassian (Jan 3, 2008)

Tahoe1, the numbers you state are for building code, and refer to 120 volts or more. 

At our lower voltages, the voltage drop can be significant... i.e. 2 volts lost out of 120 volts is trivial, but 2 volts lost out of 12 volts is significant. 

In addition, the length of the run factors in, so you cannot just say x gauge is good for 15 amps without the length calculated in... 


Those numbers are guidelines for home wiring. 


Regards, Greg


----------



## ralphbrades (Jan 3, 2008)

As Lawrence Livermore said to Kim Penny -"It would seem that the rules of Physics hold true on both sides of the Atlantic"... 

This is my guideline for Low Voltage Cabling -yes it is EU std stuff -but I imagine that it would not be too difficult with a set of tables to work out what the US/Can cables would be. 

http://www.cabbagepatchrailway.co.uk/mls/g3/eu_cable.pdf 

Here in the EU all cabling has to be certified to min 3KV insulation. I will confess to being "hazy" about US specs in that area. 

regards 

ralph


----------



## Bunker (Feb 7, 2009)

You do not want to run #12 or #14 gauge standard or UF house (wire) cable through any long runs of conduit. It may be best if you use a single conductor THHN stranded or solid #14 (20 amp rated*) or #12 (30 amp rated*). 

* 0 - 2000 volts @ 90ºC 

http://en.wikipedia.org/wiki/American_wire_gauge#cite_note-6


----------



## Greg Elmassian (Jan 3, 2008)

Again, the amp rating is NOT for low voltage, so you need to ignore that data, get specs on the voltage you want, but the real test is to use the resistance per foot and determine the voltage loss at your worst case amps. Basic Ohms law = Voltage drop in your wire = amps times resistance per foot, times feet (times two since you have to go out and back) 

Also I know about getting wire hot in the conduit... I doubt seriously that people are drawing enough current at 24 volts to heat it up. Why? Because if it was heating, then your power loss would be huge and you would have hardly any voltage to the rails. 

You really need to not try to use house wiring "rules of thumb" on low voltage applications. 

Regards, Greg


----------



## Bunker (Feb 7, 2009)

The National Electrical Code table is for AC and/or DC voltages 0 - 2,000 Volts up to 60 cycle (Hertz). 
Is Ohm's Law different for AC or DC? 
Is resistance (Ohms) is the same for direct current or alternating current?


----------



## Madstang (Jan 4, 2008)

They say that the low voltage wire you bury directly in the ground after time starts to desingrate.

I have had to dig up some wire I placed directly in the ground approx 10 years ago. All I have found is that is gets dried out...stiff, but still holds up.

If you have a large enough power supply you do not notice the drop...I have 3 power supplies 2 are 300, 1 is 200, and then a small one of 120 for a verry small area. With 1 on a run down to the end of my yard quite a ways and do not notice a difference in brightness with any the lights. And I used 18 gauge. So I truly believe that a larger power supply works best...for me.

I plan on connecting all of them with a 600 watt and placing it in my basement on the same time. Eliminating the 4 units I have in different places.

I have 4-7 watts bulbs in my houses on my outside layout, and I have lights everywhere on the layout.

Bubba


----------



## Greg Elmassian (Jan 3, 2008)

Bunker: 

No it's not different, but the current carrying capacities you are quoting are NOT accurate nor helpful for our low voltage. 

Again, 2 volts lost in 110v is nothing, but 2 volts lost in 12 volts is significant. I hope you think about this. 

Ohms law is what you need to use, and use the resistance per foot of the wire. You will see that even though the wire is RATED for UP TO 15 amps, the voltage drop on 14 gauge wire on a 10 amp circuit is unacceptable to most people. Calculate it out for yourself and come to your own conclusion. 

Yes, resistance for AC is different than DC, but that's really not the point here. (AC resistance is called something else) 

I again encourage you to look up the information yourself, there is a big difference between a maximum rating, and what is an acceptable voltage loss. 

Regards, Greg


----------



## mickey (Jan 28, 2009)

Brings several questions to mind. What size for switches and by house wire I assume you mean the solid stuff hooked to outlets?


----------



## Greg Elmassian (Jan 3, 2008)

Heavy gauge solid stands up better, but harder to handle than stranded. I'm using 10 gauge stranded, but will convert to 10 gauge solid. The stranded wire does not stand up to the elements as well. 

*
*
*http://www.cirris.com/testing/resistance/wire.html*



Greg


----------



## Mike Reilley (Jan 2, 2008)

Maybe in plainer English...the resistance of a wire depends on it's diameter and it's length. Greg provided a link to a web site that lets you find the resistance of a particular size and length of wire.

To determine what size wire you need...you need to understand how much current (amps) you locos or consists will use when running. If you are running a Big Hauler...which maxes at like 1.5 amps the size wire you need is VERY different from what you'd need for a double headed train with E-8s...which draw maybe 5 amps each. 

You want to be able to supply the amps without an appreciable voltage drop....so if you plan to run two E-8s drawing 10 amps...and your have a layout that is 100' long...meaning you need a 100' wire...it means that you can compute how much voltage loss you'll suffer with a given wire size. For example, if you used 16 gauge wire on a 100' run, that web page will tell you that it has a .4 ohm resistance. That means you'd suffer a 4 volt drop in voltage from the power supply to the track where the 100' cable ends. (ohms law...voltage drop equals resistance times amps....or, in this example, voltage drop = .4 ohms X 10 amps = 4 volts). If you used a 20v power supply, it means you loco is gonna see 16 volts at the far end of the layout (20 minus the 4 volt drop from the cable).


But, think about this....say you want the train to run at half speed...10 volts. Well, it will still pull about 10 amps....and the 4 volt drop will still be there from the wire...so it means you engine is only gonna see 6 volts at the far end of your layout....so, to keep it moving, you'll be messing with your throttle to boost the voltage.


Now...what happens if you put in 10 gauge wire. Well, the resistance for 100' drops to one fourth of smaller wire....0.1 ohms. That means the voltage drop at 10 amps is only 1 volt...so even at half speed, the variation from one end to the other end of the layout is only 1 volt. Conclusion....for big engines, operations will be far more uniform with the bigger wire. 


Now...if you're running a Big Hauler...and pulling 1 amp...then the 16 gauge wire would result in only a .4 volt drop (drop = .4 ohms X 1 amp)...meaning it will run fine anywhere, even with the smaller wire. 


Conclusion...understand how much current your engines/consists pull. That leads to the size wire you need...not electrical codes.


Well...maybe that wasn't plainer English.....


----------



## John J (Dec 29, 2007)

When I was running track power I ran feeds to the four corners of the compass. ( My layout was a rectangle then) There was a feed to the North, South, East, and West. I used Low Voltage Malibu lighting wire on sale at Home Depot. It all came to a central terminal in the middle of the layout. Plain and simple worked flawless for years. 

JJ 

PS On my first layout I soldered wire around Joints. Then went to Hillman Rail Clamps.


----------



## kormsen (Oct 27, 2009)

wiring is one thing, where i am following the texas rules - bigger is better. 
never had any electrical problems by using the standard wires, that are required for 220V housewiring. (2 to 3 mm diameter)


----------



## Bunker (Feb 7, 2009)

Posted By Greg Elmassian on 15 Aug 2011 07:56 PM 
Bunker: 

No it's not different, but the current carrying capacities you are quoting are NOT accurate nor helpful for our low voltage. 

Again, 2 volts lost in 110v is nothing, but 2 volts lost in 12 volts is significant. I hope you think about this. 

Ohms law is what you need to use, and use the resistance per foot of the wire. You will see that even though the wire is RATED for UP TO 15 amps, the voltage drop on 14 gauge wire on a 10 amp circuit is unacceptable to most people. Calculate it out for yourself and come to your own conclusion. 

Yes, resistance for AC is different than DC, but that's really not the point here. (AC resistance is called something else) 

I again encourage you to look up the information yourself, there is a big difference between a maximum rating, and what is an acceptable voltage loss. 

Regards, Greg 

I am looking Greg, but I must have forgotten a lot (FOG here). The larger the copper wire gauge cross section the less power loss per foot due to resistance. (Not that double-ought wire is the best choice.) At 24 VDC with a 15 Amp draw would be a resistance of 1.6Ώ (R=E/I) Is that correct? #14 AGW copper @ 90°C has a loss of 2.5 Ohms per kFT. 

My concern is the heat build-up from a #14 NM or UF copper wire inside electrical conduit versus 2 or 3 conductors of THHN (or better THWN) buried in the conduit. 

I personally have used #12 THHN stranded wire for my layout power (indoors) with some #16 AGW for pigtail branch conductors to lamps and an Ampmeter.




(P.S. No pissing contest here, just trying to remember.)

Sincerely,
Dave


----------



## Greg Elmassian (Jan 3, 2008)

I would first suggest that you never get your wire to 90 degrees C !! 

But your calcs on 14 gauge are correct, although remember that this is one way only, a one thousand foot run is actually 2000 feet of wire, 1,000 feet out, and another 1,000 feet back, so 5 ohms. 

I'm not sure what wire you are looking at for 1.6 ohms with 15 amps and 24 vdc, you did not specify what length run and what gauge. 

#12 inside sounds good, why not go that or the next step up. 

Concern about heating is reasonable, but I submit that if you have enough current to significantly heat the wire, you are wasting too much energy as heat, therefore, a rule of thumb is that you have excessive voltage drop on the wire. 

Go the next step up. If you investigate solid or stranded #10 wire with the THHN (I call thin) insulation for use in conduit, you will see that it is WAY cheaper than the heavily insulated landscape wire. Last time I did rough calcs, I was able to purchase 1" conduit and the wire for less than what it cost for the landscape wire, considering #10 gauge in both cases. 

I could look up the tables for heat rise on the wires, but again, I think you would be better convinced if you looked it up yourself and evaluated the information for yourself. 

So far, no overheating problems here and I do regularly run 10 amp (actually 9.7) trains... that train on the opening page of my web site draws about 10 amps. 

Regards, Greg


----------



## Bunker (Feb 7, 2009)

Thanks for the explanation Greg. #10 AGW in PVC conduit makes the most sense to me too.


----------



## Greg Elmassian (Jan 3, 2008)

No problem, believe me I agonized over this decision years ago, and that was when the "experts" were telling me that DCC outside was impossible. Also that no train drew 10 amps, or that all trains should be rated for 23 amps because of the theoretical stall current. 

When you think it through, the answer becomes clear, but the red herring is the "blanket" rules where the rules are really for household wiring. 

Back to Ohms law... 

Regards, Greg


----------



## philly33 (Apr 17, 2010)

Ok if anybody cares I used 14 gauge wire and connected to an LGB track power connector. The story of getting the 14 gauge through the PVC pipes a good one all by itself. At any rate hooked up my power source put an engine on the track and it all ran first time I moved the switch. Used split jaw track connectors and have had no problems. It may just be a simple oval but the Pond Bank and Greenbriar Short Line is up and running. Now the wallet starts taking the big hits!


----------



## mickey (Jan 28, 2009)

So I never got an answer to my question about switches. What gauge for them? Also, when running to different sides of the track, do you daisy chain or home run each one? I'm only going to have about 100' so probably won't even need since using split jaw on everything


----------



## Greg Elmassian (Jan 3, 2008)

home run... never daisy chain, in the best case you still lose voltage, in the worst, it's a debugging nightmare... 

I looked back, did not see you asked about switches specifically, but accessories.

If your switches only take momentary power, then nice light gauge wire will suffice, like 18 gauge or even finer. You could get some of the "irrigation wire" which is a bundle of 8 or 10 wires if you have a lot of switches.

By the way, to pull wires, did you leave a "pull line" inside? The stuff the pros use is a lightweight, slippery plastic. 


Greg


----------



## mickey (Jan 28, 2009)

So I guess if you use the multiple wire sprinkler stuff, you'd just split the sheathing to pull out the pair for that switch then continue to the next switch? I hear recommendations of using conduit, so how do due that? Start and stop the conduit? Would love to hear the ideas so I can learn from others experience.


----------



## Greg Elmassian (Jan 3, 2008)

It really depends on how many switches and how many are on the "route". 

I am all air power and conduit, so my air hoses are buried just under the surface and the power wire and DCC command station wires are in the conduit. 

The conduit comes up to the surface every 20-30 feet, and I bring the wires out, and then the ones continuing dive back down to continue. 

Greg


----------



## Therios (Sep 28, 2008)

many people bury conduit right under the track path or very near it. One guy here in our local club (large layout) pours a concrete base instead of using the ladder technique. So he runs conduit in all of the concrete sections. They all run back to the main panel (a large box on the inside of his shed) where he then breaks them out and wires them there. Sure sounds like a lot of planning to me to do concrete, but it is definitely durable done right. 

As someone already said... put a pull wire in ALL your conduit. And when you pull a wire, pull another length of pull wire (well string) along with the wire. NEVER pull a wire and forget the pull wire, you will rue the day!! 

A small wad of paper, tied to the string, that fits the inside of the conduit (during assembly) and you can vacuum from the other end and it will come through with practice. I have managed to pull long tubes with this method but there really can't be any complicated joints or alternate routes, just straight through. So just don't forget the string EVER!!


----------



## Greg Elmassian (Jan 3, 2008)

A 100' fish tape from the local Home Depot is well worth the $$ it costs.. 

Greg


----------

