If a have a loop of track broken up into 4 blocks, would I need a TPC for each block ?

It depends on what you want to do with your loop/4 blocks? The TPC can be either Command or Conventional not both at the same time. Command is not a big thing since several Command locomotives can operate on the same loop/4blocks at the same time. In Conventional mode the TPC is capable of operating (one) conventional or PS-1 or PS-2 locomotive. If you wish to run more than (one) conventional locomotive at a time it would require more TPC's.

Think of a TPC as a remotely controlled transformer. As far as wiring is concerned, anything you can do with a conventional transformer can be done with a TPC.

1. What was the purpose in breaking up the loop into four blocks? Are you running huge trains with multiple locomotives and many lighted passenger cars?

2. Or was your purpose simply to provide for even power distribution around the loop.

If 2., then simply bond all of your hot feeds together with a terminal strip and use the TPC to control the voltage on the entire loop at once.

If 1., then you need more transformers (TPC's) to provide additional power to the blocks.

I don't see why you would want to split a loop into blocks with separate TPCs, that would get way too complicated to use. Normally each TPC has a unique address. As the engine would move from block to block it would take on the voltage that that block's TPC was set at. I suppose you could set them all to the same address, but gosh golly they are 15A and 20A units, they should be able to power up one loop, I have one powering up three loops, only so that I can cut the power at the press of a button (press HALT first ask questions later).

More likely, you would like to cut the power to a siding on the loop so you could park a conventional loco there or put a new engine on the track.

There is a device called the BPC Block Power Controller that is an on/off device if you really wanted to cut out a block on the loop (or a siding).

You could also use simple toggle switches if you only wanted to sometimes cut the power to the block.

I have 4 blocks because I would like to run two trains conventional using toggle switches and two transformers. Then be able to switch back to TMCC when I wanted.

Two conventional engines on a big loop with four blocks.

Given the speed of most conventional engines, unless they are say older MTH or Atlas, I just don't see this being very much fun to use.

I suppose you could have two transformers, followed by two TPCs, then route thru a double pole double throw center off toggle switch, one for each block. But it would seem to me one would get tired of throwing switches pretty quick. And, timing the switches so that you don't make an engine sequence into neutral.

For the cost of four TPCs you could buy some conversion kits for those conventional engines.

It would seem to me this would be more doable with DC operated conventional scale trains and six blocks. A DC operated train could enter a dead block, and then would power is restored continue on its way. AC powered trains would jump into neutral.

Two of my Legacy/Conventional loops have 2 blocks each. One TPC400 per loop. Each block is connected to a ON-OFF-ON SPDT toggle - Up=on, Center=off, Down=18V passed through a Radio Shack 10 ohm ceramic resistor (can get hot, so be careful where you install it). A quick flick from Up to Down allows you to freeze an AF engine that has an electromechanical reverse unit in its tracks (pun intended) using a trickle of power to prevent the tripping the reverse unit into neutral (Gilbert sold these as 709 Lockout Eliminators). A quick flick from Down to Up and away she goes again. The off position (Center) is used to freeze modern engines with electronic reverse units - - many of which reset to fwd after a few seconds. The reason - - to control the spacing between multiple conventional engines on a loop at a time. How often do I use it? Not as often as I thought I would, but handy to have built in when I need it.

Hey Jimmyk, You only need 1 TPC For each loop. I use TMCC with 2 PM-1s on 2 loops but have the loops broken into 8 blocks. This allows me to do complex switching maneuvers in the yard area and switch conventional locos back and forth between loops. I use Atlas 215 A, B, OFF selector switches so I can assign a PM-1 to any block or turn it off altogether. You can do the same thing with the TPCs. For a better explaination of the system refer to Roland Lavoie's book "Model Railroading With Lionel Trains" The system works great for small to medium layouts.STEVE