Double Loop Wiring

[John Goodwin]

Good evening everyone. 

I  have recently got back into the hobby after a long break and have gone down the TT Route.(although this applies to any scale )

I  am in the process of changing my layout to include a double loop with cross over(s) and assume that if I  want to run trains on both loops at the same time  I  need to isolate the two loops at the cross overs ?

My layout is analogue - I'm too tight for DCC !

Thanks for the help and sorry  for the basic question.

Best Wishes all

John 

 

 

[LTSR_NSE]

@John Goodwin if you use Hornby points - they are self isolating. So you would only need to ensure that the polarity of both controllers matched - for when moving trains between loops.

If you use other makes of points (those that use unifrog or electro-frog) then it is recommended to use IRJs (insulating fishplates) between the sets of points to prevent short-circuits. You would still need to ensure both controllers matched polarity when moving trains between loops!

Edited June 22 by LTSR_NSE

[96RAF]

Have a read of the getting started with track extension packs. It is aimed at 00 but the underlying principles apply across scales.

[John Goodwin]

LTSR_NSE 

 

Thank you for your advice - all my points are Hornby so I  will just get another controller and be careful about the polarity.

Best Wishes 

[John Goodwin]

96RAF.

Thank you for your help. Do you have a link please ?

Best Wishes 

 

 

[LTSR_NSE]

Link to recommended thread:

 

[What About The Bee]

May I specifically ask:

What is gained by eliminating the insulated rail joiner?

What benefit does this provide?

Adding the irj insures that the two controllers never electrically meet and thus prevents short circuit.  I recognize that a locomotive can and will bridge the electrical gap, so matching the polarity between the controllers is still recommended, I simply do not understand the benefit of the converse, ie> no irj.

Thanks in advance

Bee

[ntpntpntp]

I agree with Bee - I'll always fit isolating joiners between the points of crossovers between different track circuits.  It avoids any problems with power back-feeding through the frog ends of pointwork (never a good idea).

[LTSR_NSE]

3 hours ago, What About The Bee said:

What is gained by eliminating the insulated rail joiner?

a locomotive can and will bridge the electrical gap

@What About The Bee - The only real advantage to not including IRJs is if you possess locos that pick-up one rail from front bogie & other rail from back bogie (or tender-drive locos that pick-up one rail from loco & other rail from tender.)  However I wasn’t intentionally thinking of advantages - merely looking at it the opposite way… are they necessary?

They are absolutely necessary if the frog allows electrical connectivity - however with insulfrog this is not the case.  Also if a loco/train is long enough to bridge a dead frog, it can also bridge an IRJ.

I do however agree that if you have multiple IRJs & multiple dead frogs you are reducing the likelihood of short-circuits.

[What About The Bee]

Hornby R920 has 12 insulated rail joiners for £2.99 or £0.25 each when you buy 12

One benefit to not installing irj is that you save £0.50 on the crossover.  

There is a hidden safety issue if you do not install insulated rail joiners.  Consider, unplug the controller from the wall for the inner loop.  Set the points to cross over.  Turn the outer loop controller to maximum voltage, so as to test power to the inner loop at full speed.  QUESTION: what voltage is present at the plug of the unplugged controller? ANSWER: 220 volts.  QUESTION: what amperage is present at the plug of the unplugged controller?  ANSWER: less minimal conversion losses, just about the max amperage the plugged in controller can source. 

WHY?  Voltage is converted down from 220 to 14 at the first controller and back up to 220 at the second (unplugged) controller.  In the field, we laughingly called this "Joltage" because that is going to give you a surprising jolt.  But it is no laughing matter, this can pack a punch.

÷÷÷÷

Aside from the safety issue, if irj are not installed, changing the points with mismatched polarity will short the track, independent of locomotive location. This may not be an obvious issue to troubleshoot.  What happened?

If irj ARE installed and there is a polarity mismatch, the controllers will only short when the locomotive is actually crossing over.  This will be easy to troubleshoot, as the problem source will be located betwixt the seat and the controller.

Bee

 

Edited June 23 by What About The Bee
I am not convinced the circuit breaker for the circuit connected to the second controller will detect the short when you grab the plug, due to the step down step up transformer. Is it unfused, unprotected? That can be lethal

[LTSR_NSE]

From a safety perspective therefore better practice to:

• either use a dual/triple/quad controller (with single shared PSU) so unnecessary to disconnect anything & no risk of reversing transformers.

• or isolate/disconnect unused controller from track or from its PSU (rather than unplugging PSU from wall but leaving it connected to controller) so again no risk of reversing transformers.

Edited June 23 by LTSR_NSE

[96RAF]

I agree with Bee in that not using IRJs can be dangerous if separate transformers are used and cross over polarities are mis-matched. At best the controller will trip out, at worst a high amperage short could cause a lot of damage. The unplugged controller scenario is well advertised as a no-no, having been discussed on the forum previously with regard to using several PSUs to up the power to the track.

In fact I would go so far as to say IRJs are mandatory at all cross-overs in a DC track power scenario using multiple controllers regardless of point type. Self isolation cannot be relied upon as there comes a situation where even if one point of the pair is set to crossover a short can occur. Others will say they have never used IRJs and never had a problem.

Length of loco doesn't mean a lot as very few only have pickups on one axle short even a 4 wheeler will bridge the gap.

 

 

[ntpntpntp]

The safety issue of having two controllers connected to the track with one unplugged from the mains is something that for many years has had very strong warnings in the instructions for European controllers etc.   It's interesting that the German N gauge modular standards I've been following for 20 years have now dropped the idea of connecting an accessory bus through the entire system for the same reason,  and now recommend you leave those wires disconnected at the limits of your group of modules so there's no possibility of someone else's unplugged accessory transformer suddenly having mains voltage present on the plug pins. 

As I wrote earlier, I'm with @96RAF with regard to always fitting IRJs at crossovers between controller circuits.     The mention of locos with the "American" power pickup arrangement (loco one side, tender the other side) is a fair point as these don't cope with the usual practice of setting two controllers the same and driving across the IRJs.   I use DC Cab Control wiring so I avoid the problem by having the tracks on both sides of the gap under the same controller until the train has cleared the crossover. 

[John Goodwin]

Thank you all for your advice - to be on the safe side I will be fitting insulated fishplates . I presume as long as polarity is ok then going over the join will be ok as the locos will bridge the two circuits ?

 

Thanks again

[ntpntpntp]

@John Goodwin    Yes.  With DC layouts it's usually the case (and sensible) that the two controllers are wired so that on parallel tracks the locos will move off in the same direction when the controllers are set the same.   So when it comes to negotiating a crossover with IRJs fitted you simply set both controllers to the same speed and direction and your loco will run smoothly across.