Clarification

1) Yes

2) The Bigger the better.

3) A Rev L TIU may alter this but it has worked for Modular Clubs with Buss wiring:

Find the thread on Susan Deats' filters, put them on TIU outputs and at each track power drop. Make a power block out of every 3 or so modules. If you just have a few modules make a block out of each one. Too many blocks is as bad as too few.

BUY and Use Barry's Book. It has all the answers.

Bobbie,

1. when connecting DCS to an existing layout can all the grounds coming out of the TIU be on a single Buss wire while all the hots for the Tracks be single or does the  Buss need to be Two wires side by side to feed power to the Tracks.

They are more accurately called Common wires, however, the answer is "yes".

2. If i use 14/16 Gauge Wire for the Hots for the tracks and I use a single Ground what size wire should be used for the whole ground system IE: 12 or 10 Gauge

14 gauge should be adequate.

3. On my Modular Layout I am wanting to be able to separate the Modules and I want to use Buss wiring but I want to use jumpers between the modules to keep the Buss as one run. can this be done reliably

Yes, however, use 14 gauge jumpers and ensure tight connections.

Thank you one and all

my thoughts were the same however I wanted to have a second opinion to make sure I was correct

Bobbie, if you're using several hot feeds and a single ground, it would not be unreasonable to use a 12-gauge buss for the ground (common).  That's what I use, and it's a bare wire to facilitate tying everything---tracks, accessories, lights---into it.  Also, I have it loop around the layout, with each end connected together at the U terminals.  There is also a straight jumper across the layout to the middle of the wire loop.

my thought on this was to use a Grounding bar for the Grounds

where alll the Commons come to the grounding bar and then out to one

common under the layout

hence 6 hot lines for 6 loops of track and one common for the Whole thing

But only for Track power

Accessory power is through a seperate buss system

That's the way my layout is set up, except each of the 6 hot outputsof the TIUs goes to panel where it splits into a toggled 14 gauge line out to each block, of which there are over 60.

Mine has no panel to it

and it is modular and I am going to need to rewire it

I have 2 loops on the base deck

Three loops on the next deck up and

one loop on the Top deck that runs around a dept 56 village

it is set up in 14 sections that Bolt Together

I am planning to rewire this thing as I have used basic 2 wire from transformer to Track for all of them/ and I am going to be using full dcs on this thing this year versus only 2 tracks that I used this past year. One Command and One Variable

So I will have to get a second TIU for this year and about 500 foot of wire to redo this as well as a couple of 100 Foot spools of Accessory Wire in diffrent colors

Even the accessory commons are interconnected.
I do have DCS.  Don't use it a lot.  Passive mode connection.

Common connections, the two bars are connected also.  There is a third bar.

Bars shown are electrical panel neutral bars, note the plastic ends. Electrical panel ground bars do not have the plastic, stand-off ends.