ZW-Wiring = Scary

[lionelsoni]

That's true, Rob.  Having those wires swapped is not a good thing; but it's not as dangerous as the other errors.  It is pretty much equivalent to using the wrong colors for the wires, since both wires connect to the same point at the panel.  There was a time when smaller wire was allowed for the equipment ground, for example, two 14 AWG conductors with a 16 AWG ground; but that situation was corrected many years ago and those installations are not very common.  The GFI circuit breakers now being used in newer houses should quickly catch a swap in the white and green wires.

[Deputy]

Well, in fact I have thought about writing the book that Deputy suggests.  Maybe when I get my layout finished...;-)

Dang it Bob! If you lived in El Paso I might have been able to stop over a few weekends and give you a hand with the layout. It would be worth it to get that book written!

[ADCX Rob]

...A more insidious wiring error is an open equipment ground.  You don't get a shock from it; but you don't get any protection either.  They make simple little testers for these things; but you can check the outlet by measuring the voltage from the equipment ground pin to each of the other pins.  There should be no voltage between the equipment ground and the wide pin; but there should be 120 volts or so between the equipment ground and the narrow pin.

Unfortunately, even if this test is done with the correct results, it doesn't reveal if someone has switched the ground & neutral connections at the outlet or elsewhere in the circuit.

Rob 

[lionelsoni]

Well, in fact I have thought about writing the book that Deputy suggests.  Maybe when I get my layout finished...;-)

A miswired outlet with a hot equipment ground is certainly a dangerous thing.  But it is dangerous no matter what 3-wire appliance you plug into it, whether a train layout or a microwave oven.  On balance, I believe that the best course is simply to make sure that it is wired properly and then take advantage of its doing its thing to protect whatever is plugged into it.

A more insidious wiring error is an open equipment ground.  You don't get a shock from it; but you don't get any protection either.  They make simple little testers for these things; but you can check the outlet by measuring the voltage from the equipment ground pin to each of the other pins.  There should be no voltage between the equipment ground and the wide pin; but there should be 120 volts or so between the equipment ground and the narrow pin.

[Yog-Sothoth]

Ah the power of search. Yes, the issue was discussed earlier and ChiefEagles pointed out that you cannot connect the outside rail to earth ground without killing your TMCC signal:

http://cs.trains.com/forums/1171629/ShowPost.aspx


I am a rank novice at electrical matters but I like to keep my terminology distinct by not using "ground" in reference to the secondary of a transformer:

earth ground = third prong (or pin 5 on TMCC serial port!)
track common = outside rail
track hot = center rail

"ground" = confusion

But to muddy the water further I think there are some switching power supplies where the output is connected to earth ground??

[Deputy]

Thanks BF!!! Bob has so dang many good answers posted it's tricky to find them all
If he wrote a book I'd sure buy it in a heartbeat.

[bfskinner]

He already has, almost 4 years ago, and there's probably more. Try this for openers. I found it using the advance search function. If we can't get a "sticky thread dedicated to his work, perhaps he'll write a book. Quote:

transformers

I'll give the ground problem a try. First of all, let me define some terms. In electronics, there are three similar connections that often get confused with each other. They are "ground" ("earth" in England), "chassis", and "common". "Common" means a connection among all the wires designated as "common". Its symbol is a triangle with the top side (usually) horizontal. There can be (but usually aren't) multiple commons, which may or may not be connected together, in a circuit, each identified by an additional symbol within the triangle. "Chassis" means a connection to the frame or "chassis" of the equipment. Its symbol is a (usually) horizontal line with several parallel diagonal lines descending from it. You can see that a chassis connection is a kind of special version of a common connection, with the extra feature of being connected to the chassis. "Ground" means a connection to the actual ground or planet Earth. Its symbol is the one with three (usually) horizontal lines decreasing in length from top to bottom. You can see that a ground connection is also a kind of special version of a common connection, with the extra feature of being connected to the earth. The ground symbol can also be used for the frame of a vehicle, not necessarily actually connected to the earth, like the body of an airplane. But I and many others often speak also of the outside or stock rails of 3-rail track as "ground", in a sort of modeling sense, since the stock rails of a prototype electric railroad would normally be grounded. Now we know that our trains require a voltage between the outside rails and the center rail in order to run. So we can declare (speaking in the loose modeling sense) that one side of the transformer winding(s) that power(s) the train, that is, the side that we connect to the outside rails, is grounded. As long as that is all that we are doing, it doesn't matter much which side we connect to which rails. But, if we want to operate an accessory or a switch that we will power through an insulated outside rail, a "control" rail, the wheels and axles will act like a switch to connect the control rail to the other outside rails. Therefore some part of the accessory circuit is inevitably going to be grounded since it will include the grounded outside rails. The most convenient part of the accessory circuit to ground is the accessory winding or voltage supply. With separate transformers or other supplies, this is done simply by connecting them together. When they are in the same box, the connection is usually already made inside the box. Most of the problems that folks have using these transformer accessory windings are in figuring out which side of the multiple windings have been connected together so that that internal connection can also be connected to the outside rails. Lionel has not made this any easier, since they have been about as inconsistent as possible in their labeling. I believe that I have also read here that the CW80, if connected properly for operating switches and accessories, that is, with the internal common connection grounded externally to the outside rails, will be connected backwards for whistle and bell control. This would not have been a problem in postwar days, since the whistle relay could not distinguish between the two polarities of DC voltage that the whistle control would add to the track voltage. But modern locomotives can; so they misbehave when you get it backwards, as Lionel apparently has. By the way, it is often said that transformers connected together to our outside-rail ground must be "phased", that is, connected so that the ungrounded sides of the windings have the same polarity. The only instance I know where this might be needed is when two track supplies are used in adjacent track sections with a train passing from one section to the other. This practice is a little risky, since significant difference in the voltage settings for the two sections can have the same effect, to a lesser degree, as having the transformers out of phase, that is, drawing excessive current. For accessories, "phasing", or even using supplies of the same frequency is not necessary. In fact, there are good reasons for using DC for switches even though one uses AC for the trains, as I do. Bob Nelson

[Deputy]

Yog: Have to wait for Bob to comment on this. I'm sure he'll have an explaination.

[Yog-Sothoth]

Bob advises connecting the track common to earth ground for safety.

However, doesn't TMCC rely on the separation of earth ground and track common as the two halves of its 'transmitting antenna'? I have read many times that connecting earth ground and track common will short out the TMCC signal, though I have not tested it myself.

On a unrelated point, I have also read arguments that connecting metal things on the layout to earth ground via a three-prong plug is dangerous because a misconnection in the three-prong plug could tie the metal thing to the hot side of the 120V AC line. I have no idea if this is really a danger or not.

Yog

[RockIsland52]

AMEN!

[Deputy]

I found another gem from the past. I have a postwar ZW on the way from an Ebay auction and was contemplating rebuilding it myself, especially replacing the cord. Did a search, and sure enough, Bob Nelson had the skinny on it.
I propose that Bob's responses and threads be placed in some kind of tech/repair section of the forum for future reference. They are just too dang valuable to lose.

Dep

[lionelsoni]

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!

[clickmatch]

So in the end I sent the transformer off to Ken K. in IL for refurbishing.

[lionelsoni]

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.

[trigtrax]

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.

[lionelsoni]

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.)

[joe-daddy]

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 

[lionelsoni]

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".

 

[joe-daddy]

snip

It's a 3-prong plug. I checked out the inside of the ZW and I see two solder points. A top and bottom. The cord I have has 3 wires. Green, white, black. I am assuming I am to wire the green and black together (common and ground) and solder it in one spot (not sure top or bottom) and the white (hot) in the opposite.

snip

 

For your own safety, I would recomend that you have a professional install the cord.  From your comments it seems that you have had no experience with 120 volt AC and lack the knowledge to accomplish the job.

Not trying to be a wise guy, just don't want you to hurt yourself or burn down your house.

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

 

 

[lionelsoni]

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.

[trigtrax]

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.

 

[lionelsoni]

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.

[trigtrax]

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.

 

[lionelsoni]

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.

[clickmatch]

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 =)

 

 

[wrmcclellan]

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.

[pgtr]

...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.

 

 

[lionelsoni]

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.

 

[lionelsoni]

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.