Common ground question

There is no need to connect them.

The channels on the ZW are connected because the outputs of the ZW have a connected common ground. The Z-4000 channels are independent of each other.

However,If there is a short in the Z-4000 the whole transformer shuts down.

Independent loops with independent commons makes trouble shooting much easier if there is a derailment. This is important at public displays and when people are at your house. If there is a short only the trains on that one transformer stop.

Jeff,

Each TIU has a common ground connected to each output channel. 
My question is, should I connect the grounds of the TIUs together at the outputs? 

First, they're not "grounds", rather, they are "Commons".

Next, if the transformers are in phase with respect to each other, just ensure that all 8 of the black output terminals (output Common) of both TIUs are connected together.

If you also have other transformers that operate switch tracks (particularly if they're wired for auto-nonderailing operation) or accessories, it's wise to ensure that any such transformers are in-phase with respect to the track power transformers, and that each has one Common post connected to a Common post of one of the track power transformers.

Jim,

There is no need to connect them.

I must disagree. The reason that they should be connected is to ensure that, as life goes on, the transformers remain in phase.

Wiring changes, future connection of currently unconnected loops, and unplugging/replugging transformers into AC outlets (particularly PW ZWs) can easily lead to out-of-phase conditions that can make operation unsafe. Connected Commons will immediately highlight these issues and prevent problems due to wiring short-circuits.

Additionally, if transformers that power switch tracks that are wired for auto-nonderailing operation do not have their Common lines connected to track power Common, the auto-nonderailing mechanism will not work.

The channels on the ZW are connected because the outputs of the ZW have a connected common ground. The Z-4000 channels are independent of each other.

Not so. The Z4000 power circuits all share the Common line. Try connecting one handle's Hot to another handle's Common. You will generate a short circuit.

Did not know that about the Z-4000. I thought the whole thing shut down because of internal circuitry detecting a short and shutting the whole thing down.

In running club layouts with independent loops we have gone to great lengths to keep the commons seperate for the trouble shooting advantages and to keep most of the layout running if there is a derailment. In a home layout with up to 8 independent loops this would be a graeat advantage. Think of it 8 trains running around in all there glory and suddenly the whole thing stops because of some little derailment. Where do you begin to look? The Z-4000 shuts down 2 loops and 6 keep going. That narrows the problem down.

Either way there are advantages and disadvantages to tying the commons together

Jeff,

Can I do this at the same spot after the TIU outputs?

Yes, you can.

Jeff,

So all transformers with any sort of connection to track tie in the commons after the TIU, correct

Correct!

Having all those track commons together is also pretty key to get TMCC/Legacy to work, probably another good reason to do so.

In electronics a ground is also a point of zero potential for common returns. A good example is the body of an automobile or a common bus on a train layout.  Not to be confused with earth ground.

The definition of ground is explained here. See the middle of the page about chassis ground and signal ground.

http://www.wikipedia.org/wiki/Ground_(electricity)

Dale H

Dale,

Please let's not confuse the issue. The general nomenclature for AC voltage is "Hot", "Common" and, if present, neutral. AC "Common" is not correctly referred to as "ground".

Barry

Truer words have never been spoken!

Barry, "let's not confuse the issue" indeed.

In A-C wiring, (120, 240, etc) there are HOT, NEUTRAL and GROUND.  No licensed electrician talking about plain old juice from the pole will use the word "RETURN."

In radio, telephone, and other electronic circuitry, there is a SAFETY GROUND and a SIGNAL GROUND, but the cross-over of that industry into the toy train industry has caused us to be having this conversation.

In toy trains that use A.C., there are HOT and RETURN, unless you are following some manufacturers' nomenclature which use the words COMMON and/or GROUND ambiguously to refer to the return path for digital control signals.  All the RETURNS can be COMMONed, to add further paragraphs of discussion. 

A lot of this can, and does, confuse people who do not have an electrical or electronic background, and just want their trains to run around the loop.  Trying to get everyone schooled on the nuances and then using the words consistently can be your special project, but you will die a frustrated man, I'm afraid. And I feel your pain. As a telecommunications engineer, there is scar tissue in my brain from every instance where I have tried to get people not to say "RJ45" when they mean "ethernet jack" and not to say "handset" when they mean "the phone on my desk."

Carry on, my friend...

Both Track and Accessory Commons connected at one point. There are (4) of these bars with jumpers between each bar. The (4) bars are (one) common buss.  All transformer commons, Track Commons, switch commons, and accessory commons attach to these bars.


This common bar was added as part of the 6924 relay board project.


IMO. This procedure simplifies the wiring.  First step is to take all, (ALL), commons and wire them to a common buss. If the commons were done right the only possible problem is an (Open) common. Most likely that open is either at the common buss or the point of attachment to the track, switch, or accessory.
Common wiring done, and with appropriate fusing in place,  Power wiring (Hot) to each track, switch or accessory can be completed. Problem with Hot wiring should show up at the fuse or points of connection.

I would agree, best to leave the word (Ground) out of these discussions of Toy Train wiring after the transformer.

Hi Barry

Thats for AC voltage coming into a house or house wiring. Electronics does not just consist of house wiring. For AC or DC voltage in devices,Radios,amplifiers,etc they refer to ground shared as a common return with the chassis and there is also a signal ground. Lionel uses the earth ground symbol in many of their schematics for the outside or "ground rail".  Most all automotive manuals pre 1970 use the earth ground symbols in their schematics even though the car is mounted on rubber tires. Because it is not grounded to the earth it is relatively safe from shock in a lightning storm. It is understood in the universe of the schematic that it is not earth ground. That concept was very early used in lightning rods. And widely put in use later in house wiring starting I think in the 1960s to prevent shock when people touched metal appliances..

I post this not to be confrontational but to avoid confusion for those looking at older schematics of electronic devices,including Lionel manuals.

I have serviced hundreds of electrical devices in my career and the earth ground symbol is commonly used for chassis ground. 3 prong plugs were not common practice years ago and devices were not grounded to the earth. Many devices today still use 2 prong plugs.. Floating grounds can even be engineered into high voltage AC though this is not for the squeamish.  

Dale H

Mike CT:

Beautiful work.