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I think your problem is that you're confusing a lot of things. Part of the reason for that is that there are several parallel topics running here. I'll try to lay it out straight; please forgive me if I seem to be talking down to you -- that's not my intention.

There are two ways to control your trains (in general; there are some less common methods that I will ignore for simplicity's sake): DC and DCC. They are different animals, and what applies to one does not apply to the other.

DC is direct current. It uses a power pack, which consists of a transformer (to lower the voltage), a rectifier (to convert AC household current to DC for the track), and a rheostat, which controls the amount of voltage supplied to the rails. There is also a switch to reverse the polarity of the rails, thereby reversing the direction of travel of the loco. Trains are run by using the rheostat to increase or decrease voltage, which makes locos speed up or slow down. Every loco on the rails gets the same voltage. MRC is arguably the leader in DC power packs.

However, MRC is also one of the big names in DCC systems. You have a Prodigy Advance2, which is their flagship DCC system, so nothing in the previous paragraph applies to you. Any visual similarity between the systems is incidental. The box contains everything you need to hook it up; no additional power supplies, transformers, or anything.

DCC works by applying a modified AC to the rails at a constant voltage and amperage. The throttle sends coded signals through the rails, addressed to a specific loco. Inside each locomotive, a small PCB called a decoder picks up signals intended for that locomotive and determines how much power and what polarity to send to the motor, as well as to lights and speakers (if equipped). Because track power is constant, each loco can be controlled independently of all others, as long as the total amperage of all locos does not exceed the output of the DCC system (and if it does, you can always add a booster). You control the loco by giving it speed and direction commands through the throttle, and don't have to worry about track power. While each throttle can only issue commands to one loco at a time, a single throttle can toggle between multiple locos in memory (25 for the Advance2), and send commands as fast as you can call them up.

Installing decoders is the hardest part of getting DCC up and running. You can get new locos with a decoder installed at the factory, or so-called DCC-Ready ones. For the latter, it's usually as simple as removing the shell, removing a jumper, and plugging in a decoder that you purchase separately. Older locos will probably require some electrical work and soldering -- harder, but not beyond anyone's abilities with a little practice.

Hope that helps.
Your 4th paragraph completely cleared it up for me. Now I can proceed. Thanks a lot.
 

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rvnmedic;

I can see why you're confused!
So was I, and I think, several others, because your original post is titled "Power for my new HO layout" and in it you say "It's time to buy a power pack, or two, or three", then you mention" three dedicated loops of track", and then say "My layout will be DC." All those things are descriptive of a DC controlled layout.
However, later in the thread, you say you have a DCC system. As CTValley says, in his excellent explanation, DC and DCC are indeed "two different animals." You' are new, and asking for advice, so please don't construe this as "blame" being dumped on you, but it did sidetrack the whole bunch of us into talking about DC power packs , when, it seems. you layout will not be DC at all, but DCC, since you already have that DCC system.
The "power for each 6' of track" idea refers to pieces of wire, not pieces of additional hardware, like power packs. The DCC system will provide power for all the trains on the whole layout. Since you have a fair length of track planned, using large, 14Ga. "Bus wires" run under the layout, and connecting those bus wires up to the rails, with smaller 22Ga. approx. "feeder wires" at approx 6' intervals, will assure power is available throughout the layout.
Your deduction that Power packs are for controlling trains is correct, as to their main function, but most DC power packs also have "accessories" terminals which put out AC power for things like twin-coil switch machines used to operate turnouts, and lights or other accessories. When a layout's trains are powered, and controlled, by a DCC system, (as yours will be) then a leftover power pack is a good source of either AC or DC power, as required by the particular accessories on your layout. As an example, the twin-coil switch machines used on some Atlas, and Peco, turnouts can work on either AC, or DC, power. On the other hand if you are going to use Tortoise switch machines to operate your turnouts they are DC only. Since you have a DCC system, I'm going to assume that you will be using it to control your trains. Typically, DCC systems do not directly provide power to turnouts. Turnouts, lights, signals, etc. are normally powered by a source separate from the DCC system, like the leftover power pack mentioned or possibly one of those little black cube "wall wart" devices, like those used to charge cell phones. Turnouts & other accesories can be controlled two ways. Most commonly a traditional control panel and wiring are used. The second method uses devices called "stationary decoders." These receive digital commands from the DCC controller, just as the decoders inside locomotives do. On command, the stationary decoders then send the appropriate voltage to the switch machine , which the moves the points of the turnout, sets the semaphore, turns on the light, or whatever. I have a book recommendation for you. It assumes that you are going to use your DCC system, and not DC power packs, to control your trains. The book is "basic DCC wiring" by mike Polsgrove. It explains DCC in plain English text and many color photos. I think it might help clear up your confusion. You can order a copy from Kalmbach Hobby Store or www.amazon.com I've also attached some files below that cover a wide variety of model railroad topics. Since you have your layout planned already, much of the info in them may not apply to your particular situation, but if you skim through them you may find some helpful ideas. For instance, part 6, of the "How to build a better first layout" files, covers DCC, and DC, wiring and the differences between how these"two different animals" operate.

Good Luck & Have Fun;

Traction Fan 馃檪
Thanks, TF! Between you and CTValleyRR, I have a MUCH better understanding of what I need (and don't need! LOL). I plan on buying the book before I do any wiring at all. Thanks to both of you for taking the time and posting comprehensive, helpful replies.
 

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From what I saw on a youtube vid, same subject, he used 14 gauge for the larger bus and 22 gauge for the feeder wires. (Ron's Trains and Things channel) Thanks.
rvnmedic;
Yes, there is no reason why 12Ga. wire wouldn't work for buss wires. 14Ga. is quite adequate, and the 12ga. wire will be a little more expensive. Since it's thicker, 12Ga. will also be slightly more difficult to handle, but not enough to matter, and it will work fine. The books generally suggest 14Ga. bus wires because it's big enough to handle even large club sized layouts with many locomotives, yet it's a little cheaper, and easier to bend into shape. Smaller wire has also been used as bus wire. The wire sizes quoted are only approximate, there's no hard and fast rule about it.

Traction Fan 馃檪
Thanks, TF! Between you and CTValleyRR, I have a MUCH better understanding of what I need (and don't need! LOL). I plan on buying the book before I do any wiring at all. Thanks to both of you for taking the time and posting comprehensive, helpful replies.
rvnmedic;

You're quite welcome. You can still have your three loops of track if you wish, but they won't need to be "dedicated" electrically, or have separate power supplies of any kind. With DCC, every inch of track on the whole railroad, can be one big "electrical block." Power is on all the time, in all the track.

I explain how DCC works by using the analogy of radio controlled models. Those model aircraft, cars, boats, and drones, are controlled the same basic way. For this discussion, I'm going to assume that all the models are electrically driven, by on-board batteries. (most are these days) The transmitter that the operator holds sends radio signals through the air to a receiver inside the model. The signals control what the model does.

On a DCC controlled model railroad, the DCC controller serves as our "radio transmitter." The DCC decoders inside the locomotives are our "receivers." Instead of sending signals through the air, we send them through the metal rails of our track. Instead of getting power from batteries, we get it from the rails. So, the rails serve a dual purpose. They act as both the power supplying "battery", and the "air" that carries the signals from the "transmitter" to the "receiver."

Hope that clears up some of the confusion;

Traction Fan 馃檪
 

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That's fine. Same sizes I'm using for the buss and the drops.
 

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Yup. Those sizes will definitely work.
 
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