24 AWG Wire Run Length

[Ed Kapuscinski]

I'm working on the wiring implementation plan for York, and I have a question about wire run length.
I'm thinking that, instead of tying all my feeders into a single heavier gauge bus, I'd just run them all to a centralized terminal strip (for each block).
The section of layout is only about 14' long, and any individual run would only be about half of that (7-8'), at most.

Can I get away with running the 24 AWG feeder wires for that distance? Or do I need to go up to something higher (like 16) quicker than that?

[bbussey]

My New Haven section is 16' long, and the control panel is centered.  I'm using 12 AWG for the track bus and running 22 AWG feeder wires to the rails.  The longest feeder wire is about a foot, most are shorter.  Also using 12 AWG for the accessory bus with 22 AWG feeder wires running to the various destinations.

[eja]

There are readily available calculators on line that should answer your question.  Here a couple .....

 http://www.calculator.net/voltage-drop-calculator.html

http://nebulan.net/solar/voltagedrop.asp



eja

[peteski]

Ed, you can easily answer your own question.

Calculate the resistance of the wire run.  There are many online calculators.  Here is one: http://www.cirris.com/learning-center/calculators/133-wire-resistance-calculator-table

So you have 8' run of 24 AWG wire?  That is 16' total (since electricity flows to and from the load).  According to the calculator that run has 0.411 ohms resistance.  Lets assume that a train running through that section will consume 0.5A then the voltage drop just on the feed will be 0.5 * 0.411 = 0.2V  That is very small voltage drop (instead of 12V your train would see 11.8V) so I would say that it is safe to use 24 AWG wire on the 8' feeder.  If you have some other specific values of how much current your trains use then by all means plug them into the equation - this was just to show you how to calculate the voltage drop.    Once you know how, this is very easy math.

This just calculates the drop on the feeder. It doesn't account for any voltage drop on the rails between the feeder and the loco.

[Ed Kapuscinski]

Ah, thank you! I was sleeping that day in physics...

My plan then is to have a terminal strip for each block, then tie those into the bus back to the circuit breakers.

[seusscaboose]

That's what I do

Each block has its own terminal strip locally
With 24 gauge wife running to the boosters/command station

You will be fine

[mmyers]

Ed

You should be OK for that distance. Remember too that the rails are also carrying current. So the wire plus the rail are in parallel. You can try and calculate but resistance in parallel is lower that that of each single resistor. So the actual resistance will be less then that of the wire.

Martin

[mmagliaro]

Ed, unless you've scored some 24 AWG wire on the cheap or something, I would not use that for an 8' run,
in contradiction to what others here are posting.  Here's why.

An assumption of 0.5 amp total current may be on the low side if you ever run a string of lighted passenger cars through there, or a 4-diesel lashup.  You might start seeing voltage drops of 0.5 or 0.8. 

I have had that problem (drops like that due to thin wire), and I noticed the slow-down.
I just don't think it's worth skimping on something like this.  It's only a 16 foot section.  I'd get some 20 or 18 ga wire
and just stay away from trouble.

[peteski]

I still stand by my original recommendation. Like Martin said (unless the section of track is fully isolated) then the current has another path to take (the metal track itself).  Plus, the 8' feed is the longest. All the other feeders would be shorter, and the total resistance would be lower than each individual feeder.

As far as lit passenger cars go, who uses those roof-melting 12V 60mA bulbs anymore?  Car lighting is LEDs which usually use 20mA per car or even much less if you want it to look realistic.  20mA is 0.02A per car.  IMO, what would suck a lot of current is a multi-unit lash-up with sound decoders in each loco.


I do agree that if there is no specific reason Ed has, going with heavier wire is always beneficial.