Basic wiring five separate loops, each loop 75 feet

Jim, most all of your questions are answered in the DCS companion. I think you just need some more study. Perhaps take each of your questions, one at a time, and read everything you can find on the subject. If you're still confused you can then ask more specifically about what you don't understand on each topic.

I'm fairly certain inputs and outputs are one to one, but you can use one source to more than one input if properly sized. As for the difference in running command and conventional, that is pretty well spelled out in the Companion. When power is first applied at a TIU channel input, the TIU will start sending watchdog signals out to the track. If a DSC engine sees sufficient voltage and recognizes the watchdog signals it will start in command mode. If no watchdogs when voltage comes up it will start in conventional mode. You can use the remote to set channels to conventional or command.

Again, it's all there in the Companion. I do understand it feels a bit daunting the first time, but after you work through a few configurations things will start to clear up.

You must use fixed input #1 if you want to power the TIU from track power. Or, you can use a separate power supply to power the TIU. What I like about using the auxiliary power is that I can turn on the TIU and have that part of the control system up and running before applying track power. This make is easier for me to work on switch control with the AIU without needing the track power on. But it really works just as well powering the TIU from track power.

I agree with the above, Barry's book has everything in there, but sometimes it takes a while to digest all that info. I know it took me a while and I have forgotten more than a few things since last reading it and still refer back to it. And especially if you are new to all this. Here's a few suggestions from my experiences... If you still have more questions maybe we can clarify or elaborate specifically on each one. There's a lot to some of these subjects and my reply only scratches the surface on some of them.

1. Outputs are paired, they can not be reconfigured.

2 & 3. Conventional Engines won't show up in the remote. You run them with the remote by controlling the voltage on the two Variable channels. Variable channels can be set to either fixed or variable output. You can also use the two handles of your Z-4000, one each on the fixed channels to run conventional engines. The engines would be controlled by the Z-4000 handles and not the remote.

One other way to run conventional is the optional remote controller for the Z-4000 (if you can find one). Problem here is that MTH discontinued them long ago. The Companion describes their operation much better than I could, I've never used one.

4. You can power 2 channels with the Z-4000 handles (fixed channels) without limiting your ability to run conventional on all 4 tracks. In order to have conventional ability on al 4 loops you will need something to power the variable channels separately. A single Lionel Powerhouse 180 would probably power both of your variable channels, depending on your power requirements.

5. I would not recommend using the Z-4000 aux outputs for track power.

6. Since you are using more than one TIU channels (all 4) you should definitely power your TIU via it's AUX port. You could use a Z-500 brick, or other like power source, I believe the book lists power requirements.  Also, check your Companion book first, but I believe the Z-4000's 14 Volt aux output might be able to be used for TIU power. I've never owned a Z-4000 (no personal experience), but seems like I recall seeing this mentioned in Barry's book?

Thanks so much turkey hollow rr, and rtr12 for your much appreciated responses!
that dcs book is indeed invaluable, so I will study it more. I believe we bought a z750, so I will use that to power the TIU. Soooo much info in one book! Question for rtr12…

a Lionel powerhouse 180…does it have 2 separate track outs for me to power the variable inputs on the TIU.? Thanks again to both of you!

The Lionel PH180 has a single output.  You can simple cable it with a Y-cable to two inputs on the TIU.  Remember, you can parallel two, three, or all the inputs on the TIU, you must not parallel any of the outputs.  Also, the TIU has a maximum rating of 10 amps per channel, don't exceed that.

What GRJ said above about TIU channels and the PH-180, he added some more very good advice too.

My thoughts were that one PH-180 has a 10 amp total power output, and as GRJ says above, that could be plenty of power to operate 2 (or even more) TIU channels depending on your load. If you only have one train per loop, then the PH 180 should be plenty for at least 2 TIU channels / loops of track.

Then for conventional you could use the PH-180 on your two variable channels so you could have conventional control if you needed it and then run the 2 fixed channels with the handles of your Z-4000 if you needed conventional operation there. The variable channels can be set to fixed for command operation. The fixed channels are fixed only and can not be changed to variable. For command, those channels can be set to 18 volts with the Z-4000 handles and you're ready for command operation.

And to stress what GRJ also pointed out (very good point) combining power on TIU inputs is ok,  but it is NOT ok to combine the TIU outputs, those must all be kept isolated from each other. 

@Jim bayless posted:

I have a z4000 transformer, a TIU and a handheld. What else do I need to power all 4 loops…I am assuming I will have each buss going to a terminal block and test to see how the dcs signal is holding on each loop, and install clipons to keep the signal consistent.

Is it 4 loops or 5? What matters is the length of track per TIU channel. The loops themselves don't matter so much because you're going to setup blocks of track that each connect back to a TIU channel. I believe the Companion recommends staying around 110 feet per TIU channel.

Be careful with clipons as they aren't dependable, IMHO. Also, don't fall into the trap of thinking that more track connections within a block is helpful, it is not with DCS.