Bob (lionelsoni)
I stand corrected on the composition of the case on the type Z transformer. Were they always that way? I haven’t actually seen one in years, but I’d swear I have seen some Lionel transformers with metal cases and I thought the Type Z (not to be confused with the postwar ZW) was among them.
In any event, it supports my other point that much of what is on the internet in general and the forums in particular is pap – including some of my authorship.
Bob, What happens to your trains or anyone touching the center rail if 115vac accidentally shorts to the center-rail side of your layout? Is the resistance in the secondary winding low enough so as to offer protection by way of the grounded “U”? Just pondering the pros/cons of floating trackage vs. grounded outer rails.
Roland
P.S. see edit to my previous post
I’ve never seen a metal one. The top plate, with the markings on it, is aluminum; and the base is steel. However, both of these are screwed to the Bakelite case and not connected electrically to anything inside.
If the transformer is in the off position, I’m afraid you’ll get 120 volts on the center rail and across any load sitting on the track. Otherwise, I think the transformer’s output impedance would be plenty low enough to keep the track voltage down while you have a race between the house circuit breaker and the transformer’s circuit breaker. If the transformer’s trips first, then you will again get 120 on the center rail.
You have raised a good point, Roland. I think the best solution would be to keep the ground and add transient voltage suppressors to the track. That way you’re protected from overcurrent and from dangerous voltage either between the rails or from the rails to ground. Another good practice would be to feed the entire layout from a ground-fault interrupter.
…oh yeah and for the really paranoid who operate their ZWs near water… before my better half threw out a defunct hairdryer I snipped off the cord. Guess what’s on the plug end of a hair dryer cord? A little gfci device. 
Just another cheapo source for a replacement cord.
Interesting point made by Bob about grounding the secondary common.
When I have put a 3 wire cord onto a ZW, I attach the green ground wire to the aluminum transformer core frame as it is directly attached (metal screws) to the exposed metal mounting plate on the bottom of the ZW.
Ok, I opened her up to do the cord install, and actually paid more attention. I know I need to clean up the main coil and all that, but I’m wondering if this thing needs more than just a cleaning up. Here’s some shots. In particular the lower coil is very hard and looks… just kind of wrong. But for all I know it’s resilient and will work fine. I just figured I’d show you all some pictures before I make my own decision on it.
Thanks =)
I wouldn’t expect either coil to be “resilient”. They’re densely wound copper wire with some kind of insulating coating, in the case of the primary wrapped in paper saturated with more insulating stuff that hardened when it dried. The transformer in your pictures looks about right to me.
I think you should consider the way transformers are constructed, tested, and the modes of failure.
The primary and secondary are insulated wire wrapped around a core or bobbin. After the winding the whole assembly is dipped into some form of epoxy or varnish and baked. This fills the voids between the wires, adds dielectric strength, and keeps things from moving. The core is then fitted to the laminations which have also received an interleaf varnish to keep eddy currents down.
Transformers then get a hi-pot or leakage test. Usually 1500 volts is applied between the windings and lamination and the current flow is measured and must be below some level.
There are two failure modes for a transformer. First, a winding opens, no current flows. The transformer just goes dead. The End goodbye.
Second a winding or group of windings short. In that case the short represents a zero resistance load. Current increases, heat rises and poof… Smoke. You can smell a bad winding years after it failed.
As far as collector value, transformers really don’t have any. They’ve been cranked out in quantity year after year and even the glorious ZW is now dropping in value.
I know in recent years this TMCC earth ground has been all the rage. The magic pill to solve signal problems. But the engineering of original trains never intended for the circuit to be anything but floating. A primary example of this is the fixed voltage windings of the KW. The 20 volt secondary is tapped to provide a 6 and 14 volt output. Proof against this Earth Ground arrangement.
You’ll have to fill in a few steps in your argument for me. I don’t see how having terminals C and D, respectively 6 and 20 volts relative to U, so 14 volts between them, proves that you can’t or shouldn’t ground U.
I disavow all knowledge of TMCC.
It’s really a matter of the design philosophy of the day. Accessories operated at 14 volts or 6 volts. These circuit were assumed to be floating. The common of the 14 volt accessory line was 6 volts above track common. Any common link would short out the 6 volt winding. You might think of it as hooking a voltmeter on AC to an AC source, it doesn’t matter where you stick the red or black probes it still reads AC Volts.
A similar comparison could be made for the mechanical whistle relay and the current electronic sound controls. The old mechanical relay operated on a DC voltage impressed on the AC line. If you use a Postwar tender the whistle works whether the U Post is attached to the outside or center Rail. The polarity of the impressed DC didn’t matter.
Reverse the wiring on modern sound and you’ll get Bell when you want Whistle and vice versa. Todays train motors are DC, silicon controls are DC and the philosophy is DC.
I’ll admit you need to be an “Old Crow” to understand it. Like pulling 300 volts DC off the 6 volt AC filament of some vacuum tube rectifiers. It’s from a bygone era, but so are some of our trains.
The 14-volt winding has no common with the track voltage; so you don’t use the track common for its return. This is the same whether U is grounded or floating. But grounding U insures that C, for example, is at only 6 volts, not perhaps 126, if the track common comes in contact with the power line through fault or accident.
Find a friend who knows what he or she is doing and work with them to learn first handed by a person who knows how to do this stuff.
Contrary to the world view,black is not universal ground. Transformers are called isolation devices for a reason. The reasons for using 2 wire and 3 wire are specific and screwing up or making a mistake can kill someone, most likely an innocent child or beloved spouse. Ground loops can cause problems many of us really don’t understand and troubleshooting them is neither trivial nor fun.
My 2 cents worth nothing more than the life of your grand child. . .
Joe
In America, black is probably 120 volts. In much of the rest of the world, it is 230 volts. The only places I know where black is the grounded conductor are Britain and former colonies that follow British practice. But even they have officially changed. Now the British grounded conductor is supposed to be light blue, to match the rest of Europe.
They also dropped their nominal voltage from 240 to 230, in the interest of “harmonisation”.
Much of the electronics industry has been taught that black is ground.
Thanks for making my point.
Joe
In traditional radio wiring, black is common or “ground”, not necessarily grounded. (Brown–heaters; red–B+; orange–screen grids; yellow–cathodes; green–control grids; blue–plates; gray–power line, both wires.)
Much of the electronics industry has been taught that black is ground.
Thanks for making my point.
In the electronics world Black is normally ground, just look at the jacks on your speaker cabinet. For electrical wiring homes and such. White is the common. In a three conductor BX cable (220 volt) you’ll normally find red, black and white wires. When you wire 3 phase AC it’s Black Red, Blue as hot and white as common. Most folks may not realize it but that power up on the poles is 3 phase, Your home gets 2 phases at 110 each not 180 degrees out but 120.
The changes occur in what’s been called Class 2 wiring, the 16 volts for your doorbells and thermostat wiring. Again, this is transformer isolated from your house current. Not subject to the stricter requirements of primary circuits. Toy trains fall into this class.
Most residences are supplied, along with several other houses, from a single Y-connected (except in California) 12470Y/7200-volt-or-so distribution-line phase, transformed to a center-tapped 120/240-volt three-wire single-phase service. The center-tap neutral is grounded at the service entrance and becomes white within the house. The other two wires become red and black within the house.
Those red and black wires are indeed 180 degrees out of phase with respect to ground, not 120. If the phase angle were 120 degrees, two transformers would be required; and the line-to-line voltage would be 208, not 240.
You may be thinking of a common commercial service, in which the 120-volt circuits are indeed 120 degrees apart. All three phases are usually transformed on the premises from a 480Y/277-volt service, which supplies the fluorescent lighting directly from 277-volt circuits, to a 208Y/120-volt system to supply 120-volt outlets.
So in the end I sent the transformer off to Ken K. in IL for refurbishing. [;)]
I got this from Jake by e-mail:
“Bob, am I to understand that a person should take the green wire, attach that to the case of the ZW if you are putting on a new cord? Not that familiar with the ZW stuff, even though I own a few of them I haven’t put on new cords. I did add quick blow fuses to the ZW’s, as well as the A-B-C-D posts, 32 volts, 15 amp quick blow fuses. I understand they are supposed to be between the transformer and the TIU, as a short actually draws FROM the transformer and sends higher voltage through the entire system, is that correct? Thanks Bob for all your help in the past. The switch it took me forever to understand is still working great! Atlas has asked me how in the heck I pulled that off, as they are building some of switch machine for $100.00 to handle the same thing. Jake”
You can attach the green wire to the case or to the U terminals or both. Whichever you attach it to will be grounded, so that if any dangerous voltage comes in contact with the exposed metal parts of the transformer or with the track on the layout, the house circuit breaker will trip, protecting you from getting a shock.
A short circuit from A, B, C, or D to U will draw lots of current from the transformer and will reduce the output voltage to practically nothing. But when the short circuit clears, the transformer can put out a very high voltage spike. The fuses you used may prevent this by opening the circuit before the short circuit does; but there is no guarantee that they will blow quickly enough. That is why I recommend transient voltage suppressors for folks with lots of electronics in their trains. A TVS stops the high voltage directly, whether or not the fuse blows or the circuit breaker trips.
I’m glad to hear your trackwork turned out so well!