Using both postwar and modern transformers for control on connected layout

You are actually addressing two separate issues.

The first is the fault current between two or more blocks when the transformer handles are set at different outputs. In your case, this is a big consideration when traversing blocks from, for example a loop controlled by the ZW "A" handle to a "D" handle controlled loop - one set at 7 volts, the other at 17, gives a 10 volt difference and a potentially large current must flow between the two rollers on the secondary winding inside the ZW. This is effectively a short circuit w/o any breaker protection.

The conflict between the ZW & CW is not as critical, having separate cores and the fact that the CW triacs don't mind being back-fed(ZW handle set higher), and the CW will temporarily "fold back" at 5 amps should the load exceed its capability(CW handle set higher).

The second issue is a result of crossing/bridging these blocks and the potential for high voltage spikes to be induced in the track & wiring from the collapse of high current when the bridging breaks. This is where a clamping device, a bidirectional TVS of 33-36 volts as recommended throughout the forum comes into play. This is not an issue with non-solid-state trains, but the damage from spikes is cumulative to semiconductors and failure can be immediate or much later.

Also, spikes are naturally occurring as an effect of transmitting electricity by mechanical means to a moving load along the rails(rollers, wipers,shoes, wheels, pantographs, etc.).

Circuit breakers are for the transformers and wiring, not the trains' electronics. When a breaker trips or a fuse blows out no matter how fast, the damage has already been done, whether it is adding on to the cumulative damage or it is a fatal blow.

Thanks Rob.

I have run interconnected loops before and was aware of keeping the voltage from one loop to the next the same. I had used separate transformers for this though.  The ZW is new to me so I was not aware of the effect between the internal rollers when there is a voltage difference, great thing to learn and I can educate my junior operator. When the time comes that we decide to incorporate command control, I plan on purchasing a ZW-L.  Are the internals of the ZW-L similar to the ZW in that there can be potentially be a large current flow between rollers if the the handles are set to different voltages or is the ZW-L a completely different animal design-wise?

While I have always been a proponent of using breakers to protect the wiring, the use of TVSs was something I picked up here and have them currently employed on our floor layout. I've purchased about 20 bidirectional ones with 39V clamping from Mouser since we're running postwar, MPC, and modern era locos. Do you recommend connecting a TVS between the center and outside rail on each side of the loop transition point or is having one across each of the feeders sufficient?  I know GunnrunnerJohn mentioned adding them to the modern locos themselves between the collector and chassis, but I am wary of doing that since my electrical skills are not the strongest.

We have been rearranging the floor layout to test various aspects of the final design, find potential problems, and just make sure we like the overall feel before constructing all the benchwork etc.  I'm endeavoring to start construction with as solid of a plan as I can get.

Kreuz posted:

Are the internals of the ZW-L similar to the ZW in that there can be potentially be a large current flow between rollers if the the handles are set to different voltages or is the ZW-L a completely different animal design-wise?

 Completely different, the ZW-L has a toroidal core and is fully electronically controlled. Fault currents are probably addressed in the firmware, which to my understanding has fail-safes to somehow prevent combining or bridging of the power districts to the detriment of the equipment. I don't know how it's done.

Kreuz posted:

Do you recommend connecting a TVS between the center and outside rail on each side of the loop transition point or is having one across each of the feeders sufficient?

 At least one per power district , no harm / no foul for over using them where convenient. Although we are talking microseconds and the speed of light here, the closer to the component(s) being safeguarded, the better.

I figured the ZW-L would be completely different, but just wanted to confirm my suspicion.

Thanks for the insight.  While I love the sounds and performance of the modern equipment, it's not as bulletproof as the older stuff. Thus I always use the the postwar loco for initial test runs.