Power Wire Size

One word, Daaaang!

Chris S.

Partial list from one of my web pages:  Toy Train Layout Wiring - Wire Sizes

#16 thhn solid for AC electrical - Taps to track from bus wiring.
#16 thhn stranded for AC electrical - Accessory bus wiring.
#14 thhn stranded for AC electrical - Bus wire for track on small layouts and accessories.
#12 thhn stranded for AC electrical - Variable voltage bus wire for track on a large layout and Common bus wire for small layouts.
#10 thhn stranded for AC electrical - Common bus wire for large layouts.

Holy Jumpin'!  

10 gauge stranded is my recommendation for the track buses.

George

I would not use less than 14 gauge for anything feeding track, especially on a large layout like this.

Ray,

My layout is 33 ft x 38 ft, so not quite a large as yours. My challenge, however, was due to where I had to locate the control center with all the transformers (*), switches, etc. , which was rather distant from where I needed to route the power.

 A wire run from my control center to the center of one of the two main portions of my layout was about 120 feet as it had to go around the perimeter of the room, and around several obstacles. After I installed several of these runs, I decided to run the wires up the wall next to the control center (inside PVC pipe), and down at the center of the area to be powered. This saved me about 40 feet, so now these runs were 80 feet.

 (*) I have six remote control wall outlets on the layout room walls, and these feed local power supplies for lighting. Not only is this a convenient way to turn on and off the street lights, building lights, and some accessories, but also cut down on the lengths of the wires.

 What wire gauge (AWG) should you use? This depends on how long your wire runs will be, and the expected amperage (current) they will carry. As an example, let’s look at my track wiring.

 My track wiring consists of eight 12 AWG wires, each 80 feet long, from the transformers to the TIU’s – four from each ZW-L. Each of the TIU’s supplies four distribution blocks (relays) via 14 AWG wires that are 20 feet long or shorter. Each distribution block supplies power to six track districts (mains, sidings, or spurs) via 16 AWG wires that are 12 feet long or shorter. Average current draw at any one time from any channel is about 3 amps, but this can be higher occasionally.

 You can easily calculate the voltage drop across the wire if you know the wire material (usually copper), the resistance for the wire for the given length, and the wire gauge. But an easier way yet is using this calculator:

Once you have entered the parameters, you will get the voltage drop and the resulting voltage at the end of the wire. Some transformers sense the current draw and raise the output to maintain a somewhat constant voltage, but there can be a drop nevertheless.

With the information provided by the calculator, you can decide what voltage you want to have available for your trains, and select the proper AWG to get there.

Good luck!

Alex

Alex provides good resources. 

But not, it’s an assumed/ assigned current of 5 Amps. 

The load you put on that circuit will affect everything. 

Notice 5 Amps- is 1.27 volts dropped

But at 15 Amps-it’s 3.81 volts  

My point, as always is focus on the Amps- because these are Alternating CURRENT devices. Because it’s the Current that will be your enemy-from loss of control over your trains to fire hazards.  

12AWG sizing for the wire for 15 Amps is more than adequate.. if not over kill😁

There's a lot of useful info on this site

Thanks Alex

Whatever gauge wire you select... better buy a few reels.  

Are you attacking this solo or do you have a small army to assist?

When using a calculation formula to predict voltage drop, don't forget to double the length of wire, since the power goes out and back.  This doesn't include track loss--track joints usually make weaker contact as the years go by and, if steel, oxidation sets in.

My experience has been that the difference between transformer output voltage and track voltage at the train is always greater than expected.

RJR- that is accurate as far as theory is concerned. 

But Amperage is still the only factor that matters-because at the train(load) it’s the current that will literally and figuratively bite you. 😁

tynaskos posted:

Just finishing the bones of the benchwork, trying to figure out what size power wire to run, among other things.  All I have planned in my head is 3 main lines running the entire layout which is  approx. 40 x 40 and a yard in the middle island.  

Any help and ideas is greatly appreciated.

Thx,

 Ray 

Ray, something we could do is make a coaling yard facility on the long section by the canyon area. 

Camryn

1Drummer is right.  Were there no amperage---no current draw---30gauge or smaller wire would get full voltage to the track.  It's when you started running incandescent lighted passenger cars, smoke, and a few locos on a circuit, that the high (relatively) amperage causes voltage to drop and performance nosedive.

tynaskos posted:

Just finishing the bones of the benchwork, trying to figure out what size power wire to run, among other things.  All I have planned in my head is 3 main lines running the entire layout which is  approx. 40 x 40 and a yard in the middle island.  

Any help and ideas is greatly appreciated.

Thx,

 Ray 

You don’t have a track plan on paper?

I suggest you get a guesstimate of total track footage and keep your eye on how many parallel circuits you’ll need to feed the beasts 🚂😁

Thanks to all for the replies and help.  I will have my track plan cleaned up and put on paper, it is currently in my head, not the best idea.  There are 3 of us working on the layout.  We lack the experience and knowledge of the wiring a large layout, so your alls help is very valuable to us.

Thank you,

Ray