On Circular Mils and Wire Size Selection

Over thinking way too much!

jackson

That is a great approach for a layout with long feeder runs. Recognize it is a formula that works for DC and low frequency AC power supplies. For short feeder runs the more relevant data is the current rating and breaker trip point of the power supply. If the power supply is capable of 10A then 18 GA is too small even if the voltage drop is acceptable. 

I recommend using stranded wire for model railroad hookup. It is more flexibLe and easier to use. 

Regarding your voltage drop question, 10%, 1.6V is ok over several hundred feet of wire. Dropping that much over 5' of wire could overheat the insulation. 

Thanks Tom, just the kind of answer I was hoping for.

quote:

If the power supply is capable of 10A then 18 GA is too small even if the voltage drop is acceptable. 

18 gauge would be fine if the circuit was protected appropriately.

Interesting note: Wire sizes are in MCM, larger that 0000 size. Commonly used wire size is 500MCM  approximately 400 amps Copper conductor, (90 degree C), capacity, and 750 MCM approximately 500 amps, Copper conductor, (90 degree C), capacity.   Both are way beyond model train amperage, looks more like pipes than wires.    Commercial, Industrial use.  I have use 500 MCM for service conductor on a few very large homes.  

I would not want to pay the electric bill for a home that required 500MCM service conductors!

That would be my house, 5,000 sq/ft, three heat pumps.   Last month's electric bill was $1062!

Wow, that is a lot of money that could be better spent on hobbies! When I lived in Pittsburgh and then Chicago we always had natural gas service so the heating bills were not that high. We have 5,000 sq/ft at the coast in So Cal so the heating is never over $100 and the A/C is almost never needed. Downside is no basement for the trains. 

Some of the train collectors out here have separate buildings on their lot for the trains. Many of the pre-war and early post-war homes are on flat lots with enough space for an outbuilding. 

Don't I know it, but we seem to be having a real winter this year!

2000 sq ft high r factor ranch.  Quadrafire wood stove.  Gas heat bill for January, $90. Delaware Valley.

Had a 25' X 42'  building for trains @ last house, never again.

We have no gas available, or I'd be using it.  With heating oil at $4/gal and up, that's not a bargain either.

Keep in mind an all electric home has one energy bill.   Those with multiple utilities should add the bills to compare.  Note that Natural gas is relatively cheap at the moment, but can become more expensive related to demand.  The current drilling frenzy here in the north east has changed a lot of energy consumption thinking.  Methane is readily available, 1st hydrocarbon out of the wells. 

 5 degrees this morning, we should see a heat wave of 40 sometime this week. I had wired one home that had a Geo-Thermal Heat Pump.  Maybe more efficient than pulling heat from 5 degree air. 

Getting back to Scott's original question "My question is: what is acceptable and expected for good track performance? Why wouldn't a 5% or 10% drop be ok over a 5 ft length allowing me to use a smaller wire?"

I usually use a nominal loss of 2 volts max on any run with a design 10 amp load max. So running command at 18 volts input means that the minimum track feed at any point with a max 10 amp load would be 16 VAC.

Also keep in mind that wire length means the total length, out and back.

This means that the practical max run length for 16 awg is about 25 ft, and for 14 awg about 40 ft.

Now realistically it is highly unlikely that you would ever be feeding a full 10 amps load through any one track feed. This would equate to at least two or three large trains with lighted passenger cars etc, so the load would almost certainly be spread out between two or more feeds.

Note also that the voltage drop in a wiring run is not dependent on the feed voltage; only on the wire size (CM) and the load.

Hope that helps.

Rod

2200 sq ft. Electric heat. Bills for Dec- $50, Jan $60 and just got Feb $70. Ouch! NW New Jersey many below zero temps. Insulation R-59 attic, R-23 walls.

10A through a 5' length of feeder (5' in each direction) results in a 1.61V drop. The thing is even in open chassis wiring 22ga is only rated 7A. 18ga provides the same voltage drop over 13 feet. 14ga is 33' for the same drop. 

For small layouts 18ga works ok. I see no reason to use smaller wire. 

Operating in conventional mode the effect of the voltage drop is noticeable, in Legacy command mode it is not.

Here are 14 ga solid drops on Atlas code 148 two rail track. 

90 degree bend and flattened "spike head" with the smooth portion of needle nose pliers:

quote:

When I lived in Pittsburgh and then Chicago we always had natural gas service so the heating bills were not that high.

How many years ago?

Energy prices seem to have gone up dramatically over the past several years.
I guess that just about everything has.

My propane bill for the mountain cottage was $3,000 plus, covering since September. [1k gallon "submarine" tank]. Temp is maintained at 45 degrees, although water is shut off pipes have not been drained through the drain-down system.

We visit occasionally which is why the moderate temp is maintained instead of shutting everything down. Unfortunately my layout has been dismantled ['08]--place is for sale.