Portable Layout Power?

Yep, that should do it. The Base3 doesn't put out power itself (unlike the MTH TIU), so the setup is the base3 connects to the ground for the layout, and then you use a power source to power the rails.  One question, why would you buy multiple bricks to power the track? Are you using power districts (ie basically blocks) and will use 1 brick for each district? If you plan on running it where the layout is continuous, then you could do multiple drops off one brick. Are you planning multiple bricks to have enough power to handle multiple engines at the same time? In theory I guess if you wire them in parallel you can distribute the current load across three bricks (ie 3 bricks wired in parallel @ 100 watts=300 watts total power available), but might be better just to buy a higher output brick (and these days I don't know what is available). Others will chime in, but your basic concept is correct. On larger layouts you can get voltage drop if the brick is at one end of the layout and a feed wire runs a long distance, but I I kind of doubt that (using a larger gauge wire for the power wire can help offset that).

John,

The word "ground" can be very misleading, causing big headaches.  (If you want to know why I'd be happy to give you a 2 or 3-paragraph explanation.)

Just connect the single wire from your TMCC or Legacy base to an outside rail somewhere around the layout and you should be fine.

Mike

John,

Go with the LIONEL "ZWL" Transformer and be done with it.  You wont regret it, believe me!! It will cover all your Bases!!

Fredstrains

One brick should be sufficient to run three trains on the same main line.  If you have multiple main lines, a brick on each is appropriate so a breaker trip on one line allows the others to continue operation.

A word of caution on phasing the power supplies - your house wiring has two 120v legs on opposite phase.  A brick plugged into a socket in one room may be out of phase with a brick in the next room.  The combined bricks could delivering a 36+ volt potential to the track.  Not good for train electronics.

Voltage drop is proportional to the distance to the power source, the gauge of the power wires, and the number of track joints.  Use 12g or 14g wire to supply power to distant portions of the track.  (low voltage outdoor lighting wire works well).