Mark Gurries

On Jun 27, 2016, at 6:57 PM, lehighman@... [WiringForDCC] <WiringForDCC@...> wrote:

I am building a new layout using DCC and want to install signals.  I understand that this requires I set up a detection block(s) for each signal.  Blocks are also set up to distribute power throughout the layout or to add reversing sections. My question involves my confusion regarding how each of these blocks fits together.  

Electrical blocks do not exist in the prototype and are use to contain shorts.  The ultimate length limits  are defined by the booster distance coverage.   Within a given booster district, these blocks are created by the use of DCC circuit breakers or some device used to disconnect track power.  The Power District tracks are defined by functional working areas (Yards, Brand Lines, Staging) or key tracks like main line versus industrial sidings.  Think of what people will be doing and how to prevent what other people are doing from electrically short circuit protection point of view.   A well design power district plan will allow a lot of operators to remain operating trains despite a given engineer dealing with a derailment.

Signal blocks are defined by "control points" which typically defined by turnouts that control main line train flow (passing siding or interlocking).  

Between control points on the main line, detection blocks  are spaced apart so there is ample notification for given trains about other trains so they can stop.  Everything is defined by an operational safety point of view which has nothing to do with electrical blocks..   For model railroad purposes, it simply becomes the length of the longest train length you wish to model on you layout. 

Example:  Simple loop with 3 signal aspects.   If you train length is 12Feet long, you will need 4 signal blocks which means you need 48 Feet of loop track to always allow the train to see a green signal ahead of it.   The block are as follows:  

1) The block the trains is in
2) Red Block behind the train protecting the train from behind
3) Yellow Block also protecting you from the train from behind.
4) The Green Block ahead of you.

There is a more to this especially if you want to follow some prototype implementation of signalling.

ABS signalling only protects you from trains BEHIND you going in the same direction.  Does nothing to help you SAFELY see what is ahead in terms of trains but would indicate if you were taking the main line or passing siding.  Dispatcher still authorizes all movement via train orders.

APB is bidirectional ABS that does allow you to see both train AHEAD AND BEHIND.  Dispatcher still authorizes all moments via train orders.

CTC is dispatcher controlled signals.  Authority is granted by signal indication.

Some single track signal systems only monitored control points and did not care about trains between them.  All the signals along the way were advance signals telling them what to expect to see at the next control point..

I isolate power blocks by cutting each rail going into and out of the block – a total of 4 cuts per block.  I feed power to the block through feeder wires connected to both rails about every 3 feet.  What cuts do I make to set up a detection block?

No problem here from an electrical connection point of view..

You now have to translate you DCC power districts into signal blocks by looking at the length of the electrical blocks relative to your train length.

IF a power district block is long enough to hold a train, it can be used as a signal block too.

If a given power district block is to short length wise, it must be combined with another adjacent power district block detection wise to create one that is long enough.

If one was to design a layout with signals.  It is alway best to define signal blocks first and then see if they can be used as power districts.  Typically it works out very well.

As best I can tell, I only need to isolate one rail for each detection block


with a cut on either end and run the power lead to that rail thru the detection circuit with the other rail being powered by the normal track feeder.  Is this correct?


Best Regards,

Mark Gurries
Electrical Engineer
DCC Website & NMRA DCC Clinics:

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