Some help planning power for new layout

While I'm not familiar with your particular Transformers, Putting 2 power sources in parallel is always a BAD idea. One will pull more of the load and overload while the other idles.

Go with one for Sidings, One for Loop and isolate the sidings from the loop by using an insulating pin in the middle rail right after the switch.

Adding a Transorb across the power wires and from each power wire to Earth ground will protect engines from spikes. Use bi-directional ones, they cover positive or negative spikes.

You will also have trouble matching the voltage and the lower voltage unit will start getting back emf effects from the reverse current flow.  Bad idea.

"Adding a Transorb across the power wires and from each power wire to Earth ground will protect engines from spikes."

DO NOT add anything from the power wires to earth ground.  There should be no electrical connection between the floating outputs of the transformers and earth ground, especially if you are running TMCC/Legacy.  A TVS (Transient Voltage Suppressor) across the transformer output or from center to outer rail is sufficient.

OK, thanks for the replies.  I'll dispense with the idea of hooking up two power sources to the same block.  Someone on this forum gave me that idea 3-4 years ago when I indicated I had broken my loops/mainlines into blocks with a single transformer per block.  I was lamenting the voltage drops due to trackside accessories, and the forum responder suggested piggybacking two transformers in parallel.  Live and learn, I guess.

Buiding on Andy's idea, I'll go back to my original idea of breaking each loop in half, or 2 separate blocks, and run one transformer to each. Then, I can put a powermaster on each as well.  Requires 2 more powermasters but I like that price tag better than new bricks.

I think that answers my questions #2 and #4 above.

Any input on whether the A post or U post goes to the center or outer rail?  Or, should I just dig out the old instruction sheets?

Lastly, Dale, can you explain more about the TVS you're suggesting?  I'm not familiar with that at all.  I'm a bit of an electrical novice.  Can I get one at, say, Radio Shack?  And, what do you mean "across the transformer output or from center to outer rail"?

You want to buy some 1.5KE36CA Transient Voltage Suppressors.  At Mouser.com they are P/N 511-1.5KE36CA.  I suggest you buy a dozen while you are at it.  Be sure to get the CA type, which is the bipolar type for AC voltages.

The TVS is connected in shunt across the output of the transformer - one lead to A, the other to U.  Or you can connect them where your transformer leads connect to the track.  Do not connect the TVS in series with a power lead.

The TVS provides a bypass path to clamp any surge voltage spikes that exceed the 36 volt rating of the TVS.  Only the tips above 36 volts flow through the TVS.  This avoids an overvoltage spike from reaching the electronics of the locomotives.

If you are using a Powermaster, include a TVS at the transformer's output and another at the Powermaster output.

The only practical, effective way to parallel transformers is with a pair of fixed voltage transformers such as the Lionel Powerhouses when linked to a TPC [Track Power Controller]. With variable voltage transformers it is virtually impossible to accurately match voltages on the two units.

TVS??--see photo below including one wired accross ZW A and U posts.

Thanks so much Dale for the description/specs and Dewey for the picture.  My layout is looking like it'll have 6 transformers, 5 with powermasters and 1 purely for conventional operation.  Plus, with 2 transformers and 2 powermasters on the Christmas Tree layout, Dale's estimate of 12 TVS' was 1 shy of what I need.  At $0.55 each for a 10pack, I'll buy an even 20 for about $11.00 and keep a few extras around.  Seems like a VERY small investment to protect hundreds of dollars of train electronics.  THANKS SO MUCH for the tips and tricks.  I wish my Grandpa was still around.....he was an electrical genius in the electro-mechanical era, and I should've picked up more from him while he was alive.