Theoretical Electrical Questions: Do more feed wires means less heat?

The real issue here is current draw..

in the authors comment, I see no mention of isolated individual track blocks…

so, the current draw creates the heat-which is a byproduct of the transfer of energy.

To reduce heat, reduce the current draw

the first step should be to reduce the distance the current must travel on the rails, not just the distance on the feeders.

it is my determination that even a simple track layout that runs more than one locomotive, should be divided into equal isolated individual track blocks and fed with feeders in parallel.
why?
Because as you add loads, which are heat dissipators,  the total resistance decreases, as does the heat.

And the benefit of parallel wiring, to smaller track sections also decreases the force-or voltage, required to overcome the inherent resistance of the track and wire; this also diminishes the heat byproduct.

This animal we call electricity, has an amazing talent when sent through parallel paths….the total resistance of the total circuit will be less than lowest value of the smallest resistor in the paths.
That decreases the heat byproduct

Drummer,

Thanks for the great picture and analysis.

I have read it three times though, and I am sorry that I don't totally understand it.  :-O

Does it mean that my system is good, bad, or neither?

My track blocks will have isolated center (hot) rails, because that is the rail into which I will be inserting the plastic pins on each end for each block.

Should I be putting the plastic pins in both ends of the outside neutral rail as well?  (My multiple feeds to each power block will include both hot and neutral.)

The system I have proposed for what I view as speed and simplicity in wiring (for me) has sure created a lot of controversy. :-)

And let me repeat for emphasis, that I'm not going to be running 16 foot lengths of 18 gauge wire as feeders.  The very longest would be around 8 feet, and most would be 6  feet or less.

Thanks,

Mannyrock

Well actually, your 18ga is a little light. 14ga is more like it for longer than a 12 inch feeder. But you probably won’t experience any issues. Maybe the 18ga wire will drop a volt or so, but the TMCC system can handle that nicely.
Time to run the trains! And less kibitzing!

If you are using block wiring, you don't need to isolate the outside (neutral) rails, unless you are using a track section as a detector section, which you likely are not doing.

When you say track feeder, are you running the 18 gauge from the control panel/block switch to the block/track involved? 

Normally from the block switch or transformer, I would use a heavier gauge wire (like 16), then you run the feed wires that solder to the track off of it.  If your layout is small and you have only 1 feed wire to each block, then using 18 would likely work, but personally I would bring the power to the block using a larger gauge and then run the 18 gauge feeder(s) off of that rather than use 18 all the way.  It sounds like you have a small enough layout the 18 gauge approach may be doable. I don't think you will have trouble with heat using 18 gauge unless you have something drawing a lot of current.

Heat is mostly a non-issue for #18 wiring at the usual maximum current of ten amps, the issue really is the voltage drop at higher currents.  25 feet of #18 copper wire has a resistance of .16 ohms.  At ten amps, the power dissipated by this amount of wire would be 16 watts.  While that will probably warm the wire to the touch, it's not going to burst into flames.  Also, it's VERY unlikely for you to be drawing anything like ten amps, especially running conventionally!

The real issue here is the voltage drop and it's effects on running.  That would be my primary reason for recommending a larger gauge wire for the main power feeds.  I used #14 wire for all my runs out to distribution points, then #18 wire for the short drops from the tracks.

Boys, I believe that there will be no material drop in voltage if I run three sets of 18 gauge feeder wires to each isolated block, and those blocks are no more than about 10 feet of track in total.  That's' what I am doing here.

This will allow me to hook up virtually everything from the inside of my control box, while its lid is open and I am standing up, and not underneath the table.

Guess I'm going to be forced to finally go to Harbor Freight and buy one of their El Cheapo Voltometers.    Maybe it'll show that I'm wrong.   If so, believe me, I will confess and beg forgiveness for my sins!  :-)

Thanks

Mannyrock

Mannyrock, 3 #18s to carry the hot to track should not give greater voltage drop and 1 #14.  You will find voltage drop through the track.  Do make sure your ground (neutral for the AC purists) is of equal ampacity, and have frequent drops to the track.  There is voltage drop on the ground circuit & outside rails just as on the hot.

While the bottom of the line HF multimeters are not of Fluke accuracy, they are good enough for train work and no great loss when dropped on concrete or into the river

@Mannyrock posted:

Boys, I believe that there will be no material drop in voltage if I run three sets of 18 gauge feeder wires to each isolated block, and those blocks are no more than about 10 feet of track in total.  That's' what I am doing here.

I believe you're right, and I thought I pretty clearly said so!  If one 18ga wire is sufficient, three would be more than sufficient.  FWIW, I have #18 wires going from my new yard switch panel to each of the tracks, and I'm not worried at all about the current draw or voltage drop!  Again, this is a non-issue, especially going to short tracks!

GRJ, when I built my layout about 1992, I had a lowest level yard with many blocks.  I also had some 18-gauge 8-conductor wire.  So I used that from the control panel toggles.  Figured I'd be having a hand on transformer throttle anyway, so could compensate for voltage drop.  When I added DCS 10 years later, I had very poor signal strength, virtually unusable.  I eventually removed the #18 & replaced it with #14.  No more problems; great signals.

You may want to wire up one or two tracks and check signal strength under load.

I have all the tracks wired, and the DCS signals are fine on all the yard tracks.  I can't imagine what the difference between #14 and #18 had to do with the DCS signal, there's no reason it should change anything, all other things being equal.

Imagine that the heavy current flowing for the train also has an effect on the voltage of the signal??????

@RJR posted:

Imagine that the heavy current flowing for the train also has an effect on the voltage of the signal??????

Sorry, but I'm not buying.  First off, for a siding, you would never be drawing more than a few amps.  Also, I've can't imagine how the 60hz current in the wire is affecting the 3.27mhz signal, even at maximum current.   I assure you it's certainly not a documented phenomenon, at least none that I've ever heard of.

I'll say it again.  IMO, changing the wire from 18ga to 14ga for a siding didn't affect the DCS signal at all!  Note that I'm not saying that you didn't experience a change in the DCS signal strength, what I am saying is it wasn't because of the wire size.  Obviously, something else changed during this rewiring job.

My readily evident ignorance self-explains why I will never get a command control system!  I just couldn't bear it!

John, thanks for joining in with your excellent advice, as always.

Mannyrock

I can't believe this topic is still being discussed!  Hasn't the initial question been answered?

On the surface, this seems like a penny wise pound foolish discussion.  The cost of wiring on your layout is actually one of the smallest expenses you will incur.  To use wire smaller than #14 going to the track either full loops or to blocks is a savings one MTH 20- freight car, maybe.  For the drops to the track I would use #16 or better but then I always over build.  If you want to run #18 which I probably would not, run it to your Barrel Loader.

An electrician friend used the water hose analogy.  The farther you go in order to get an equal amount of water you have to use a bigger hose.  Electricity works pretty much the same way.  The longer your layout is powered up and the more trains you are running the bigger the hose you need.

It’s not about the cost, I think the original poster is about the ease of using 18 ga wire and would that work ok.

i think the answer is yes…probably…

Here's a Wire Combination Calculator that might answer some of the combined run questions.

I have been watching this thread with some amusement, the OP's original premise was a "large layout," but somehow we got down to a maximum run of 8 ft!

Anyway, from a voltage drop perspective, 1 foot of AWG 18 will offer about the same voltage drop as 2.5 feet of AWG 14, for the same current. FACT!

As far as heating goes, most O gauge transformers, when used as intended, can't put out enough current to make wire heating an issue for sizes larger than AWG 18, unless you start to put them in parallel which is not a sport for beginners.

Here are some handy rule-of-thumb numbers about voltage drop. These are round figures, plenty close enough for our work.

10 AWG -  1000 ampere-feet per volt

12 AWG - 600 ampere feet per volt

14 AWG - 400 ampere feet per volt

16 AWG - 250 ampere feet per volt

18 AWG - 150 ampere-feet per volt

20 AWG - 100 ampere feet per volt

So, in the OP's case, if he has 8 feet of AWG 18, for a total out-and-back circuit length of 16 feet, he will have a voltage drop of about .85 volt at a current of 8 amps. (8 amperes x 16 feet = 128 ampere-feet, divided by 150 = .85.)

If he used AWG 14 his voltage drop would be 128/400= about .32 volt for the same 16 feet and 8 amperes.

There is no magic to this, it was all figured out better than 100 years ago!

@gunrunnerjohn posted:

Here's a Wire Combination Calculator that might answer some of the combined run questions.

John,

Thanks for the link!

@PLCProf posted:

There is no magic to this, it was all figured out better than 100 years ago!

The only "magic" is that #18 will be more than sufficient for the stated use.

Prof,

A maximum run of 8 feet of the 18 gauge wire out to a track, would permit almost a 15 ft x 7 ft layout.  I'm just a novice, but that's pretty big in my book.  :-)

(Of course, I know that some folks have gigantic layouts, so that would be small to them.  If mine ever gets that big, I'm running 14 Romex and calling an electrician to hook up the ends!)

Mannyrock

@Mannyrock posted:

A maximum run of 8 feet of the 18 gauge wire out to a track, would permit almost a 15 ft x 7 ft layout.  I'm just a novice, but that's pretty big in my book.  :-)

Well, that's only if you put the transformer in the dead center of the room.  Also, it would have to be a straight line wire to the track from the transformer stretched out like a clothes line!  You'd be amazed how much more wire it actually takes to get to the track from the typical transformer location.

P.S. Mine's not that big a layout, but with my new freight yard it's almost 40 feet long.  Big are those basement filling monsters that have several thousand feet of track!

Do more feed wires mean less heat?

Yes,  more feed wires mean less resistance resulting in less heat.  Just that simple.

Charlie

Well, heat = volts x amps (for our purposes), so the OP is pushing 8 amperes through a voltage drop of about .85 volts which makes the heat generated in the wire .85 volts x 8 amps = about 6.8 watts.

I think 6.8 watts in an eight foot wire isn't going to exactly light it on fire!   It'll probably get somewhat warm to the touch, that's about it.

@gunrunnerjohn posted:

I think 6.8 watts in an eight foot wire isn't going to exactly light it on fire!   It'll probably get somewhat warm to the touch, that's about it.

Exactly right!

Regardless of the Ohm's Law calculations, I would observe that my experience is that an AC voltmeter at the end of a block in which a heavy electrical load train is operating always seems to indicate that there is greater voltage drop than The Law would indicate should be found.  That is the ultimate test of whether wire is heavy enough, connections are good enough, and track joints are adequate.

I would also note that the output voltage of a transformer may or may not be what the dial or integral voltmeters indicate, and may drop when a good load is applied.

One way to find the cause of voltage loss is to connect an AC voltmeter between any two points on the same feed.

But the 8 ft run would not be the sole set of wires feeding power to that power block, it would only be one of three sets!  How's it gonna even get warm?  Its not.  :-)

@RJR posted:

Regardless of the Ohm's Law calculations, I would observe that my experience is that an AC voltmeter at the end of a block in which a heavy electrical load train is operating always seems to indicate that there is greater voltage drop than The Law would indicate should be found.  That is the ultimate test of whether wire is heavy enough, connections are good enough, and track joints are adequate.

Any extra voltage drop due to poor connections and/or track joints is a whole different matter.  Doubling the size of the wire will have no effect on those factors, and they should be properly addressed separately!  If you have a specific sized copper wire with a specific current flowing in it, I can assure you that it will very closely track Ohm's Law!

Thanks for everyone's exceptional input and comments.

I now draw the curtain on this one.

Until next time, . . . .

Mannyrock

I am pleased to see so much interest in this topic.
safety and knowledge are two things that can never have too much activity.