How much does voltage drop affect TNCC

Unless you have cruise control, the voltage drop will affect a TMCC engine similar to how it affects a conventional engine.   There is really no difference.  With cruise control, it will have much less effect as long as the voltage drop isn't extreme.

Cruise control keeps about 20% of the voltage in "reserve" to compensate for loading.  As long as the voltage doesn't vary more than about 15-20%, most cruise control will keep the speed nearly constant.  If the voltage falls below what was in reserve, the cruise system doesn't have the power to maintain the speed.

I'm with you on the 9.3 amps for #12 wire? Always thought it was 15 amps for #14 and 20 amps for #12 at 120 volts anyway. Smaller wire will increase voltage drop, as in our trains, but I would think you could go pretty far with #12 or #14 wire for train power with very little voltage drop. May have to study up on this a bit myself.

FWIW:

I run 14ga bus and feeders on my 10'x16' layout. Each of my 2 main loops has just 4 pairs of feeders fairly evenly spaced at roughly 10' apart.

The transformer( 180w brick) is closer to one side of the layout than the other, some of my wire runs are as long as 12'. Voltage at the output side of my TPC is the same as anywhere on the track.

Lionel recommends a minimum of 14ga wire when wiring a TPC to the track so thats what I did.

IMO 14 ga is big enough without being overkill. I am very pleased with the results.

The issue with model trains vs. 120V wiring is voltage drop, not ampacity.  If you drop three volts in a run to an outlet for 120V wiring, no big loss.  However, if you drop three volts from your 18V supply, you've cut your track voltage significantly.  That's the reasoning behind larger gauge wiring for model trains.

Any idea about the 9.3 amp max rating on the #12 wire as the OP stated in his 2nd post? Have actually witnessed the voltage drops with 24 volts on long, small wire in my working life (just a worker, not an engineer or anything).  I understand about the voltage drops, especially with the lower voltages, but I don't get this part with the max amps so low? 

Hey. play with this voltage drop calculator based on NEC standards. Take a 14' x 9' L-shaped layout with a buss from end to end. Assume 18VAC with an allowable voltage drop of 3% for 25 feet. Transformer at one and you want 6amps at the other end.

Here is the result:

Reducing the distance to 5' (a drop from the buss to the track, results in 14awg.

Then try reducing the voltage to 5VAC (which runs a conventional can motor engine at a reasonable speed) and the wire size gets very large to keep a 3% drop.

I don't see any of it effecting the TMCC signal until the engine isn't getting enough volts to operate. 14? perhaps.

It's not the signal you have to worry about.  Without cruise control, speeds will vary considerably with a couple of volts drop in the track voltage for the same throttle setting.  As you say, TMCC will run down to 12-13 volts, how well or how consistent it runs is another matter.

FMH,

The TMCC signal is not affected by the voltage drop.

There is 14awg for the output supply from the 180 watt powerhouse.

Then there are two scenarios

1. The 180 watt powerhouse is connected directly to the track or buss. In this case, you are correct- it doesn't make sense to use heavier wire downstream.
2. The powerhouse is connected to a ZW-C, TPC or TIU. Here the 14awg is only a short run to a controller. ( or direct from a ZW or ZW-L) Using heavier wire makes sense from the controller to the track to reduce the voltage drop.
3. Conventional operation is more sensitive to voltage drop as lower voltages are needed and any drop can be significant.
4. The resistance ratings for 1000' are very low, so at shorter distances, the wire doesn't become a load.

I found this voltage drop calculator that allows all of the inputs. A 25'-50' buss is not unreasonable for a small to medium layout. 14awg works ok, to about 30', unless you want to have the full 10amps at the end for 18vac.

Change it to 5vac for 6 or 10 amps at the end, and you need some heavy stuff.

I can see why the Dealer Display Layouts from the 50's used a solid bar buss.

On a follow-up note, the chart came from here: American Wire gauge and current limits and is for a single conductor ,whereas, the NEC table is for a 3 conductor. These are for ampacity and not voltage drop.

Sorry, I thought the Original Poster (person that started the post) was Ffffreddd?  Same Ffffreddd that posted the 9.3 amp max.  How many Ffffreddd's are there? I'm confused?

Going to have to fiddle with some of these calculators, but I tend to agree with your line of thought on everything else. And I still do not get the 9.3 amp max part either, no matter who posted it.

Other thing I didn't know was about the NEC and not being able to use larger wire on a 15 amp circuit. Not that I know the NEC very well, but I always thought it was the other way around, you could use #12 on a 15 amp circuit, but you can't use or reduce down to #14 on a 20 amp circuit. Learn something new every day!

Yes, the written word is much harder to interpret than the spoken word! Maybe I missed a post as I didn't see an attachment either? I do see a lot of posts here where someone is offended and I really don't think that was the intent of the offender. Just because of the writing or way it's written. It is difficult for me to accurately put my thoughts in writing most of the time, and then some are gifted writers. Oh, well so it goes.

Fred, you did imply the word signal in the title of post.

"How much does voltage drop affect TNCC" (sic TMCC)

TMCC is control signal.

In any case, after all the semantics are argued, the TMCC signal is not affected by voltage drop, but the operation of a standard (non-cruise) TMCC locomotive will be significantly affected by voltage drop.