Some people power different sections of a layout from different transformer outputs and attempt to run trains between those sections by setting the controls to the same voltage. If they don't get the voltage, waveform, frequency, and phase almost perfectly matched, a fault current flows when a train crosses the gap, and voltage spikes that are dangerous to modern electronics-intensive trains are produced.
If the transformer outputs come from the same transformer, the situation is particularly dangerous, because traditional Lionel transformers do not protect against overcurrent between the transformer's outputs.
In this risky kind of operation, there is no hope of matching the voltages unless they are in phase. But, even with a proper block setup, there is some risk of getting the blocks assigned to different outputs accidentally. So, even with no intentional connection between outputs, it is safer to have them all in phase with each other, to reduce the chance of fireworks when you make a mistake in block assignment.
This all has to do with the track voltage, not the accessories. There is no particular reason why their voltages, waveforms, frequencies, nor phases need to match. A good example of such a mismatch that causes no problem is the DC voltage from a capacitive-discharge circuit powering an anti-derailing turnout.
When an accessory uses the outside-rail common as its return, as opposed to a separate wire back to the transformer, the current in the outside rails is the sum of the train's current and the accessory's current. If those two things are supplied from voltages that are in phase, their currents add and increase the voltage drop in the outside rails. But, if they are supplied from voltages out of phase, the currents subtract--and decrease the voltage drop. It's not a big deal; but it helps a little.
Bob Nelson
I don't understand your last comment about powering accessories out of phase with track power. and how that might reduce voltage drop. Out of phase was something I thought was to be avoided at all costs.
Please explain.
Thanks
From reading previous post I can answer one question for you and that is stranded or solid doesn't matter 14 gauge is 14 gauge
Life's hard, even harder if your stupid John Wayne
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Stranded wire of a particular gauge has the same amount of copper and the same resistance, and can safely carry the same current as solid wire. You can make the choice entirely on the bases of ease of use and cost.
You may come across the myth that stranded wire is better at high frequencies. It is not. The "skin effect" that is alleged to give stranded wire an advantage by increasing its overall diameter is exactly compensated for by the inclusion of air gaps among the strands. (There is a very special kind of stranded wire, with insulated and woven strands, that is better--and expensive.) In any case, the skin effect is negligible at the 60-hertz power-line frequency.
Yes, use a layout common. Uninsulated wire is fine at the low voltages that we use. After all the track rails themselves are uninsulated and we touch them all the time.
Having the transformers for track power in phase is a good precaution against accidentally connecting outputs together; but it is not an adequate substitute for avoiding that practice. Always power both tracks from the same source before running over the gap between them.
There is a small advantage in having accessories' supply voltage out of phase with the track and using the outside rails for the accessories' return. The out-of-phase currents cancel somewhat and thereby reduce the overall voltage drop.
Thank you so much for the information.
With the price of wire so high, my cheapskate side would likely have led to me erring on the small side for the wire, you have saved me from an expensive and time consuming mistake.
A follow up question, if I may, are we talking stranded or solid conductor wire?
Also, I intended to use a common ground for all transformers (I do know how to put them in phase). Is this OK from a safety perspective? And can I use uninsulated wire for this?
There are two considerations in selecting wire gauge, safety and voltage drop.
For safety, you should use wire heavy enough to carry safely the maximum current that your transformer can put out. For the Z and ZW, this is 15 amperes and 14 AWG.
The wire selection for voltage drop is more of a judgement call. The track itself is very roughly equivalent to 16 AWG, which has a resistance of about 4 milliohms per foot, or 200 milliohms total out from the transformer and back along 25 feet of track. A train that draws 5 amperes will have a 1-volt drop at the end of that track, which is probably noticeable. I would suggest 14 AWG or, better, 12 AWG, for feeders on a layout of your size.
You should supply accessories and turnouts with the same 14 AWG that you need for safety. The control wires, on the other hand, can be considered to be current limited by the impedance of the accessories and turnouts, so much lighter wire will not be unsafe there.
You should avoid any situation where transformer outputs (terminals A, B, C, or D) of your transformers ever get connected together, as when running between tracks powered by different transformer outputs, especially outputs from the same transformer. This latter kind of fault is not protected against by the transformer's circuit breaker.
Because of this shortcoming in the Lionel designs, it is a good idea to supplement the single circuit breaker with individual breakers on the various outputs. Although you would do this for safety, you might want to use breakers with lower ratings for accessory circuits to allow use of lighter wire. For example, a 10-ampere breaker can safely feed 16 AWG and a 5-ampere breaker can safely feed 20 AWG. You can find automatically resetting thermal circuit breakers suitable for layout use at automotive parts stores.
I am sure I have seen guidelines for wire size for different applications on the layout, but I do not remember where, so I appeal to you all for help.
I am re-building an O gauge layout that is U shaped. One leg is 18' , the bottom is 22' and the last leg is 12'. There is a double track main line around most of the outside edge with two reverse loops inside those. It started out as somewhat smaller layout with O-42 K-Line switches and curves with a coulpe of O-31 lionel switches where space would not allow for the O-42. The last time I was running a long train the couplers parted, allowing the engines to exceed track speed limits and resulted in a brief flight and crash landing to the celler concrete floor. I saw it as a "sign"
I replaced all switches with K-Line O-72, and all O-42 curved track with curves ranging between O-72 and O-96. A few pieces of O-54 kind of snuck in to one of the reverse loops where I didn't have the space.
I run post war, conventional modern, and tmcc locos. Power will be from 3 Lionel Z's and a ZW.
I need wire size suggestions for track power bus, feeder , and switch machines as well as UCS tracks. The control pannel is located at the bottom of the U shape to cut down on wire distances.
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