Electrical Wire Question

I think you described the difference.   No difference as far as performance carrying power.

Thanx, John - the word "primary" threw me off. 

Paul

Paul,

   I agree with Guns, I use the softer core good 14 Guage stranded wire for my FT DCS layouts.  This softer wire is exactly what I meant by good quality 14 Gauge wire, I probably should have described what I meant as high quality.  As you noted the softer more easily workable wire is what I recommend for wiring a DCS layout.  I even use the 16 Gauge multi strand high quality on the Legacy side of my DCS/Lagacy layout. 

PCRR/Dave

What I do with my wires under the layout is to use plastic tie wraps and small screw eye style hooks to run the wires through. The tie wraps keep the wires in place on long runs.

I would agree that 14 gauge wire is very good for wiring most layouts. However if you use a transformer with more then 12 amps per line 12 gauge wire will work better as it will carry the current better then the 14 gauge. Also if you have a long run of wire, over 100 feet long I would go up one wire size to be safe from voltage drop, wire size number gets smaller as the size gets larger; example is 18 gauge wire can safely carry around 7 or 8 amps, 12 gauge wire can safely carry 20 amps.

Lee Fritz

Measured voltage drop of 14ga 40 foot run was 1 volt, if that ....

Kerrigan posted:

Measured voltage drop of 14ga 40 foot run was 1 volt, if that ....

So from what you mention about voltage drop in 14 gauge wire, an 80 foot run of 14 gauge wire will drop 2 volts, correct? That can add up on a very long run of wire so I would definitely use a larger size wire for a longer run of wire.

Lee Fritz

Voltage Drop - Calculator.net

Here you go, calculate voltage drops.

That's a great calculator since it does a calculation (simple but effective) using the source voltage. Note that 12 ga wire carrying 20 amps for 100 feet drops about 6.35 vac. That's ok for 120 vac house wiring voltage, but for 18 vac such as we have on the train wiring, the voltage drop of 6.35 vac leaves only 12.65 vac on the far end when you carry 20 amp ac over a hundred feet. Tables of gauge versus amperage that are meant for house wiring and 120 vac are not useful for train wiring amperage limits.

I have long runs of wire outside and the voltage doesn't drop that much! I imagine there's other factors? I use finer strand outdoor low voltage wire. I see a volt or two drop at the connection. I see slightly more on the track, depending on how long the block is.

 I think you'd need a really big house or tiny wire to lose 6.35 VAC!

If it has shiny, relatively inflexible insulation, it's probably from an automotive application. The insulation is designed for harsh environments, with temperature extremes and vibration. The term "primary wire" is a vestigial automotive industry term that describes, from an historical sense, the wire that provides 6, 12 or 24 volts from the battery to the primary side of the ignition coil. The high-tension wire from the secondary side of the coil goes to the center contact of the distributor, and other wires of that type go from the distributor cap to the spark plugs. That is called (or used to be called, when cars still had ignition coils and spark plugs) "secondary wire."

Many terms are used by industrial suppliers long after the actual use has expired or is not even understood by the next generation of people in the industry.  Many manufacturers still use the term "primary wire" to describe any low-voltage wire that is usually found in auto parts stores.

Unless someone else on the forum tell you that I'm wrong...

Pine Creek Railroad posted:

Paul,

   I agree with Guns, I use the softer core good 14 Guage stranded wire for my FT DCS layouts.  This softer wire is exactly what I meant by good quality 14 Gauge wire, I probably should have described what I meant as high quality.  As you noted the softer more easily workable wire is what I recommend for wiring a DCS layout.  I even use the 16 Gauge multi strand high quality on the Legacy side of my DCS/Lagacy layout. 

PCRR/Dave

Hi Dave - I've been buying Southwire primary wire from Lowe's and Home Depot but it only comes in 20 ft. lengths.  I found it on Amazon for a good price in 100 ft. lengths (about $18 per roll).  It is advertised on Amazon as "Primary Wire" but I'm skeptical about ordering it thinking that it may be the stiffer, shiny plastic type of insulated wire.  I guess I'll take a chance and order a roll of red and black from Amazon.

Thanx and good to hear from you -

Paul 

The auto store primary wire is softer. I use the red/black 2 conductor speaker wire. It works well. Some of it is copper clad aluminum so I go up a gauge when I size it.

If you can find MTW (Machine Tool Wire) it has a soft outer insulation and is quite flexible. The stiffer stuff like Lowes and HD have is most likely all THHN these days (not sure what that stands for, but personally I don't like it). If found, the MTW should be available in larger spools at a better price than the 20' spools. I don't know what lengths the automotive wire is available in?

Thhn is what is used in construction.  I used 12AWG stranded for my whole layout except for the drops.  Works great.

Ken M

*  multi-strand more flexible than single conductor
*  single conductor has slightly higher current capacity at DC or low frequency simply because it has more copper (i.e. no gaps between multi-strands)
*  multi-strand has slightly higher current capacity at higher frequencies (skin effect)

There is no skin effect significant difference with stranded wire than with solid wire unless the strands are conductively insulated from each other. That is the reason for Litz wire which has many strands that are all insulated from each other. A common misconception.

Since the wire strands are shorted everywhere in a standard stranded wire, I don't see any way that skin effect enters the picture at all.  This is a common misconception that has no basis in reality.

Here's one of many pages discussing Skin Effect and Types of Wire.

This is a useful discussion!

GRJ - thanks for that calculator.

I used THHN 14-gauge wire for my PRR Panhandle.  Based on this discussion I may go to 12 gauge or even 10 gauge for the track power buses as the layout is nearly 3x larger.  Previously, I ran individual wires.  For the new layout, I will be using Red/Black zipcord (parallel wire).

George

Takes forever to get here but the Turnigy brand is the best stuff I have ever used.  Very soft and no memory.  I do some RC flying and at times come really close to max in terms of the amps.  The stuff holds up well.  It is Turnigy brand wire.  Just google it :-)

These always prove to be interesting discussions.   Commercial wiring usually sees wire upsized for two reasons. One is length, My general rule was 200 to 250 ft or more you should be considering conductor up size. Parking lot lighting a good example of longer conductors.   Multiple conductors in a conduit, sees a significant increase in conductor size, 6 or more in a conduit. More conductors in a conduit, each conductor is de-rated, current carrying capacity is diminished, or the wire sizes are increased accordingly, there are charts based on rated insulation values.  

Nether really applies to Model railroad, though it is interesting to note that conductor length adds quickly.  Example: (5 ft) from control panel to the wall. Up the wall to ceiling (8ft).  (12ft) across the ceiling.  (8ft) down the wall, opposite side of the room, to a remote track section, leave (8ft) final track connection under the layout. (41) ft of wire just to get across the room.  Figure one track circuit (2 wires)  82 ft.  3 track circuits. 246ft of conductor. 

IMO,

Mike CT.