A question about the PECO Plan25 ... Bere Alston circuit diagram

[mikepaling]

Can anybody please explain what the wiring inside the purple circle on the attached diagram actually .... and why.
I don't understand at the minute :-(

Cheers Mike

[emjaybee]

I'm not 100%, but I think the issue is that the 'plan' creates a reverse loop, so the diagram explains how to wire a switch to prevent a short circuit.

Someone with better wiring skills than I will be along shortly to confirm.

[chrism]

I'm not 100%, but I think the issue is that the 'plan' creates a reverse loop, so the diagram explains how to wire a switch to prevent a short circuit.

Spot on - that siding is the apex of a turning/reversing triangle, thus the polarity of that siding's rails must be switchable so that they match the polarity of the rails beyond the insulating joiners.

[ntpntpntp]

There is another approach you can take with a wye formation (or reverse loop) which is to arrange the DPDT switch so that R1 is fed from either the left or right branch of the wye.  Some folk find it easier to understand (rather than creating the cross-wired connections to reverse the polarity).

As is sometimes the case with Peco plans, I don't necessarily agree with all the placements of the feeds, there's often "back-feeding" of power into the frog end of points instead of following a basic rule that power should feed into the toe end (the blades end). 

Here's where I would add a feed to make it easy to access the left branch of the wye (and the DPDT switch could be connected to)

[mikepaling]

Thanks Nick for your reply ... things are starting to make sense!

I am still not sure how to wire the DPDT switch on the isolated section and also link it to the Power point you show on your diagram.
Do I flip two separatae switches or can they be mechanically linked???

My brain is getting really confused about this!!!!

[Bob G]

@ntpntpntp is spot on as always.

If you don't want the reverse loop issue (and the trains themselves would not have done that in real life) just do away with the run of points and curves ST-5/ST-4/ST-3/ST-6 in the fiddle yard. Alternatively just relay the fiddle yard to have two or three tracks per route.

You would still have the Bere Alston - Gunnislake fork where the reversals take place, which I guess is the whole point of the model layout's design. Just easier wiring.

Oh and for those who worry about these things, the real Bere Alston had rail overbridges, not underbridges, where the two routes split, and the goods shed approach was from the other side of the station (which in the model, as in real life, has been lifted). Another LSWR main line in the southwest ripped up by the western region.

Sorry for the historic diversion.

Bob

[Bob G]

Thanks Nick for your reply ... things are starting to make sense!

I am still not sure how to wire the DPDT switch on the isolated section and also link it to the Power point you show on your diagram.
Do I flip two separatae switches or can they be mechanically linked???

My brain is getting really confused about this!!!!

Think of the DPDT switch as two side by side single pole double throw switches. But it is one switch lever, which throws two sets of contacts at the same time.
The feed and return wires come from the feed location P1 on the drawing, and go to one end of the DPDT switch. The centre terminals are connected to the R1 power clips. There are additional wires crossing over the back of the switch so that when the switch is set one way, the P1 (left hand side) goes to the R1 (left hand side), and when the switch is thrown the other way, the P1 (left hand side) is connected to the R1 (right hand side) and vice versa.
In that way, the power at the track is switched, i.e. reversed, so that it is different to the entrance to the reverse loop track, and is now the same on the exit from the reverse loop.

Bob

[mikepaling]

Thanks for the various VERY useful replies and ideas .. my brain is slowly getting there !
I have just found a wiring diagram on the ,net that looks like it works ... I am attaching it now.

[Bob G]

Yes it is clearer as every feed and return is a different colour. The Peco plan used the same name for each feed and return and i think that was confusing you.

[ntpntpntp]

That diagram you've found of wiring a wye looks very much like one I may have drawn over someone's plan, it's got all the hallmarks of the way I do it in Visio.     As you can see, it's connecting the trunk of the wye to one or other branch instead of cross-wiring the DPDT.