Understanding Power Blocks

[SteamGreaterThanDiesel]

I'm in the early stages of planning a layout.  It will be powered by a old ZW - 250 Watt. It basically consists of an outer loop and an inner loop.  The two loops are connected to each other by a right and left turnout.  I was thinking of having one ZW outuput power the inner loop and the the other output power the outer loop.  My logic being, if the turnouts keep the loops seperated, I can run two trains (one per loop).  If I want to run one train, that can use the whole layout, I have to just remember to use the other throttle as it switches loops.  

I started researching blocks.  There were plenty of posts/vidoes/articles of how to hook them up, but not good ones (that I found) on how to use it. Plus a lot were on DC powered trains.  I want to make sure I understand the basics.  Are my assumptions below correct?

1. At first, i thought the  single-pole-double-throw switch killed power to the tracks.  Now, I believe that killing power is only really for sidings to park trains.  To accomplish this, only 1 CAB would be connected to the siding

2. Assuming I have both CABs connected to each power district, then the  single-pole-double-throw switch, is really dictating which CAB powers that section of the track.  Assuming I have CAB 1 control train A. As I'm following train A around the layout, I flip the switches to have CAB 1 power/control that section of track. 

3. I shouldn't have a tain longer than the powerd sections to reduce risk of shorts; in case the two adjoining sections are controlled by different CABS.

4. According to Bob Nelson, in this post  http://cs.trains.com/ctt/f/95/t/74912.aspx, I shouldn't use the two outputs of the ZW, but instead use different CABs. (I don't want to rehash that debate. I'll assume he's correct)

5. My inner loop has reversing loops in it. Apparenlty that complicates matters. But I need to grasp the basics before I get to that. 

Bonus question.  Why are power supplies called CABS?

Sorry for the long post and thanks in advance

 

[lionelsoni]

1.  I suggest using SPDT-CO (single-pole-double-throw-center-off) switches for all the blocks, whether a siding block is used for parking trains or not.  The center-off feature gives you the option of completely shutting the block off or connecting it to either source of power.

2.  Right.

3.  Even the shortest train will occupy two blocks at a time as it moves from block to block.  So you should keep all the blocks that the train occupies, powered from the same power source (or shut off, using center-off switches) until the last powered rolling stock leaves the block.

4.  Using two outputs from the same transformer is indeed more dangerous than using separate transformers, because a fault current evades the transformer's single circuit breaker.  If you follow strictly the operating rule of never letting a train cross the gap between separately powered blocks, there will be no fault.  But sooner or later you will slip up and get it wrong.  A simple fix is adding circuit breakers to the individual transformer outputs (which Lionel should have done but didn't).  If you want, the added circuit breakers don't need to be rated for the full transformer output (15 amperes for the ZW), but only for the likely load of a single train.

5.  You don't have to do anything at all special about reversing loops (or wyes or any other track geometry that can reverse a train).  That is one great advantage that 3-rail track has over 2 rails, even if it doesn't look very prototypical.  When a 2-rail track loops back to connect with itself, the left and right rails get swapped and connected to each other, creating a short circuit.  With 3 rails, the center rail always stays in the center and the outside rails always stay on the outside.  They do get swapped left-and-right, but they were connected together anyway, so no harm is done.

[SteamGreaterThanDiesel]

Thank you for your clarifications and recommendations.  It was a big help

[BigAl 956]

Bob is correct. You really do not have to make special considerations when moving from one block to another in the Lionel world.

I used home wiring switches for my control pannel. If you need to switch a loop from one ZW control to another a 3-way switch, SPDT, will work nicely. You do not need center-off unless you need to park the train and shut down.