Question about common/ground

Outside rails can share the common.  The only time outside rails would need to be isolated is if using track activated accessories (crossing gate, crossing flashers, block signalling, gateman, etc.) with a section of insulated outside rails.

EDIT: I didn't mention wiring for DCS, since I remember from previous posts that Vin is not planning for that, but if one were wiring for DCS, then I'm not certain what the correct answer would be.

Thanks @SteveH !

If you use a shared common, it is wise to uprate the wire size.  For example, if you're using #16 center rail feeders and three tracks, use #12 for the shared common distribution wire.

@KarlDL posted:

If you use a shared common, it is wise to uprate the wire size.  For example, if you're using #16 center rail feeders and three tracks, use #12 for the shared common distribution wire.

That's a great point.  Yes, if one foresees the possibility of using multiple Hot circuits simultaneously, increasing the wire gauge for the shared common bus would be a good idea.  The often overlooked common would be carrying the same amount of current as all three of the other wires combined.

For example, if a layout's three Hot buses were carrying 5 Amps each, the Common return would be carrying 15 Amps.

@KarlDL posted:

If you use a shared common, it is wise to uprate the wire size.  For example, if you're using #16 center rail feeders and three tracks, use #12 for the shared common distribution wire.

@KarlDL Thank you for sharing this

My opinion is not to use 12 AWG.  14 AWG would be adequate.  Having wired a couple of 20 Amp circuits for my shop, the 12 AWG wire is infinitely harder to work with over the 15 Amp 14 AWG wire.  Again just my opinion.

I used #14 for all my runs from the distribution panel to the drops.  I was running the Vision Line Big Boy around the mainline with all the smoke units active.  No matter where I measured on the layout, I have minimal voltage drop when the locomotive comes by, and I lose about a maximum of .5 volts from the distribution panel to any place on the mainline.  I see no reason for #12 on anything but a pretty long run.

Not advocating #12 for track feeds, just for home runs from power supplies to shared commons on multiple outer tracks.  I'm using #12 stranded from power supplies to block disconnect switch groups and fan-out terminal blocks at 3 points around the layout (mainly because I had some 500' reels left over from a basement wiring project in a prior home).  Otherwise #14 feed buses, #16 track drops, and #18 outer signal rails.  I'm not doing shared commons, except in the yard, where current draw will be minimal.

I am sorry that I did not differentiate between stranded and solid. Stranded would be easier to work with but as GRJ insinuated is overkill. But if you had 500 feet laying around it may be worth using. And not that it is any of my business but a check of local building codes might be in order using stranded wire for house wiring.

The house was in Chicagoland, where the fire departments have written residential conduit requirements into all local building codes.  Pulling solid through conduit is, well, challenging, to say the least.  So stranded is pretty much standard there.  FYI, I'm a electrical registered professional engineer.

When I get done laying and wiring Fastrack I will have two independent loops running Conventional off 2 MTH Z-1000 Transformers except for one 45 crossover, Using a Dremel cutting wheel I cut the connections for the one track to the center on both sides of it and wired a jumper to the 2 track pieces to keep power to the hot except where the hot rail breaks at the crossover. I've used 12 gauge stranded for my Buss wiring and 18 gauge  stranded for my track feeders with TVS Diodes at every track connections as I had a lot of that wiring laying around from when I used to do electrical jobs on the side for my buss wires, separate hot and common for each track, for ease in troubleshooting down the road and labeling all the wires and color coding. Outside Track One, Red for Hot, White for Common. Inside Track 2, Orange for Hot, Grey for Common. In addition to the hot and common wires color tape, for remote switches wires are also marked with Blue to Identity them and the same system with Yellow for Uncoupling Track. I have a different shade Red and Grey that will be my Aux Power colors that will feed off the Aux Terminals on the smaller inner Track Two and I have some AC-DC and DC-DC Adjustable Buck Converters on hand for whatever needs different voltage requirements. Right now I am using 5 amp Automotive Fuses and TVS Diodes on the outputs of the Transformers until I get some of the Airpax Circuit Breakers to replace them. Thanks for all the great knowledge out there that is so willing to share great information. You all have taught me a lot to want to do it right. I'm learning more everyday!

@KarlDL posted:

Pulling solid through conduit is, well, challenging, to say the least.  So stranded is pretty much standard there.

You win that round!  I saw a pair of guys trying to pull solid wire through a conduit for my septic system installation, they finally gave up and got stranded wire. I'm not sure why they started with solid, I can only suppose they already had it on the truck and didn't want to make a trip for the right wire.

Often when pulling wires through conduit a lubricant is used.  Unfortunately this time of year, the lubricant can freeze.   Larger wire pulls, powered equipment is used.

Often, wire specification on a job require solid conductor to size #8.

Solid conductor is usually less expensive than the same size stranded.

@Mike CT posted:

Solid conductor is usually less expensive than the same size stranded.

Probably a moot point if you can't pull it through the conduit!

Only Steve H answered the question about common ground.

I'll just add to Steve's reply by saying that as a DCS user I only segment the power rail, all commons are tied together. Careful, common and ground are not necessarily the same.

When you think about an engine passing through a segment (block) the majority of the current is flowing to the rails on the one feed to the block and yet there is an entire common rail with several drops that provide more that adequate return path to the transformer. I am assuming all drops and feeds are done in pairs.

I cheated and use whatever I could find in my box of cut up wires. All of my feeders are 12 gauge stranded wire, some only a few feet long. I have a few 18 gauge drops but most are 16, may be one or two 14 ga. drops.

@turkey_hollow_rr posted:

I'll just add to Steve's reply by saying that as a DCS user I only segment the power rail, all commons are tied together. Careful, common and ground are not necessarily the same.

One issue with DCS is that the track and power feed from the transformer actually form a transmission line for the RF signal.  That being the case, keeping the two feeds the same length has the potential of improving the signal quality to the track.  How much of an improvement is pretty hard to quantify given all the other variables that enter the picture.  However, given that fact, I did run power and ground to all my track drops, I figured it wouldn't hurt to try to keep the signals as clean as possible.  I don't think it hurt anything, I have great DCS signals all around the layout.

@gunrunnerjohn posted:

One issue with DCS is that the track and power feed from the transformer actually form a transmission line for the RF signal.  That being the case, keeping the two feeds the same length has the potential of improving the signal quality to the track.  How much of an improvement is pretty hard to quantify given all the other variables that enter the picture.  However, given that fact, I did run power and ground to all my track drops, I figured it wouldn't hurt to try to keep the signals as clean as possible.  I don't think it hurt anything, I have great DCS signals all around the layout.

I started trying to remember that transmission line theory and reflections when I realize the engine produces a complex load. I did recall enough to convince me of the desire to creating blocks in the power rails. It would probably take a pretty gross mismatch in feeder lengths to cause issues but as a practical matter it is easier to wire parallel feeder wires.

I almost sprung for twisted pair cables in anticipation of running TMCC/Legacy. But, naw.

Interesting topic.  For DCS wiring, isn't it important to run power and common for each separate loop connected to each fixed and variable output on the TIU?  That way the signals are connected to and from each track feed in the "star" pattern?

Mike

@IRON HORSE posted:

Interesting topic.  For DCS wiring, isn't it important to run power and common for each separate loop connected to each fixed and variable output on the TIU?  That way the signals are connected to and from each track feed in the "star" pattern?

Although not mandatory, that is the best way IMO to wire for DCS.

I'm not sure loops have anything to do with it for DCS. When you segment the power rail into blocks the topology doesn't matter so much. The idea is to limit any possible reflection or duplication of a single DCS packet on the power rail. There is no DCS recommendation to segment the common rails and my copy of the Companion states this as well.

In my case I only use the two fixed channels, one will feed the 1st level and the other feeds the second level. I have a pair terminal strips at the output of each channel so all feeder pairs are out and back to these strips. I have 5 pairs of feeders for the first level and each has two or three drops (one per block) connected to them. That's star wiring. (Second level coming this spring.)

I also tie all transformer commons together at the TIU channel outputs so both channels' common sides are connected electrically anyway. I thought I saw a 9 once, but when I looked back at my remote it displayed a 10.

@gunrunnerjohn posted:

Although not mandatory, that is the best way IMO to wire for DCS.

That always did make me scratch my head. In the purist sense the commons should be segmented.

Given the signal characteristics, it makes the most sense.  The reason that the "magic" light bulbs and DCS filters sometimes improve things is also due to the fact that they're simply terminating a "transmission line" and minimizing signal reflections.

I don't presently own any MTH PS2 or PS3 locos.  But the topology of my intended layout wiring provides for isolation of two mains and auxiliary tracks that will facilitate insertion of an MTH TIU in the future.  And, being a retired high-power RF engineer, I get the transmission line loading concept when applied to train wiring.  I know I've gone too far if I attach my Rhode & Schwarz network analyzer to the track wires!

@KarlDL posted:

I know I've gone too far if I attach my Rhode & Schwarz network analyzer to the track wires!

It would be illuminating to do a little network analysis on the track signal however.

I've seen fist fights almost start over who got to the R & S that day.    It wouldn't surprise me if there are reflections in almost every block.

@gunrunnerjohn posted:

It would be illuminating to do a little network analysis on the track signal however.

Actually I do have a Smith Chart analyzer (from the Ukraine) at home that covers the Lionel and MTH frequencies but never thought about using it for model railroading since I get all 10's on MTH DCS packet error computations and pretty solid Legacy performance.