Can we connect 2 loops like this via DCC?

[nik_n_dad]

Hi.

We're using the kato double-track superelevated track for a large portion of our
layout. We will be using the double crossover to let trains move between the
inner and outer loops.

Additionally, part of the track plan includes a line that starts from the OUTER
loop, goes a number of places, then eventually comes back and re-connects with
the INNER loop. This 3rd line does not reverse the direction of the train.  An overly-simplified diagram is below.

We will be setting this up to run DCC.

Are there any issues with doing this? Do I need to place insulated joiners
anywhere?

Thanks

Mike & Nik

[CaptOblivious]

Topologically, that's the same as a single cross-over. If you've got power going to each of the loops, and the turnouts are power-routing, you shouldn't need to isolate anything. If the turnouts are not power-routing, you'd need to run an additional feeder to the red track. I run a similar topology on my desk all the time from a Digitrax Zephyr and no isolation.


Now, this could all change if you're going to be doing anything even remotely fancy…

[KenS]

I agree with Capt O. that as long as you wire up the inside and outside loops so that they're in the same phase (i.e., the "red" wire goes to the rail furthest from the center on both, or vice versa) and use a "power routing" turnout, that will work. That's also assuming both tracks are fed from the same command station (if one used a booster, you'd need a double rail gap, because connections between track sections fed by different supplies always need a double rail gap).

However, there is one thing to watch out for: in your diagram, the connecting track diverges from the inner loop towards the inside, and joins the outer loop from the outside.  This means that the frog of one switch faces the outer rail of the other.  And "power routing" only applies to the frog rail, the outer rail always remains hot.

This means that all that separates the two polarities when the switches are thrown for the straight routes is the insulation between the two frog rails where they meet the frog.  If there's any chance that's small enough that a wheel could bridge the gap, you'd have a short that could weld the wheel in place if the circuit breaker didn't trip fast enough.

What I'd do is gap both rails of the connecting track at each end with insulated unijoiners, just past the switch, and run a third feeder to the connecting track.  Then the rail nearest the frog would be dead unless the switch was thrown towards it, eliminating any risk of a short.  With DCC, as long as the three feeders (inner, outer and connecting) are in phase, this will all work fine.  With DC it would be a bit more complicated, as you'd probably have two power packs and would need to choose one to use for the connecting track.

Note that Kato's double-crossover has an insulator in the middle between the frog rails to do exactly this. That's the reason you always need to feed both sides of each track on the double crossover (not a problem when it's in a loop, but if not you need extra feeders on each track; I speak from experience).

[CaptOblivious]

KenS: Good point. Notice, however, that the new Tomix turnouts (circa last year) are not as you describe them: They route both rails, not just the frog rail.

That said, even older Tomix turnouts had an option for disabling the power routing, which in these kinds of cases, worked for me.

[nik_n_dad]

I plan on using kato #6 turnouts, so it's always in power routing mode.

Thanks for the tips....this was very helpful!