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)