Do I need to modify Peco points for DCC?

[Ian McAulay]

First of all, I haven't decided on DC or DCC for the layout I'm working on. However if I choose DC now, I want to be sure that changing to DCC later involves as little upheaval as possible.

I'm aware (from my 00 layout) that with live frogs as Peco do them, there is a potential issue of wheel backs shorting against point blades of the opposite polarity. What I don't know is whether the blade-to-stockrail gap on Peco electrofrogs is so huge that this isn't a problem. Any experience here would be worth hearing.

I also know that the solution in 00 is to saw through the closure rail and then bond it and the blade back to the adjacent stockrail. (That was always my practice anyway with handbuilt track in the past.) It looks do-able on left and right turnouts by cutting away the plastic base and sawing through the closure rails in the sleeper space immediately adjacent to the crossing. Again, any experience or advice would be handy.

And what about the Y points? It looks as though the whole thing is likely to fall apart if you cut the closure rails as there is only one chair between the only possible cut and the hinge for the blades. (Interestingly, I had the same problem with the Peco code 75 Y point in 00.)

Thanks!

Ian

[B.Meldon]

If your back to back is correct on all the wheel sets you will have no shorting issues.
In this regard it is the same with DC or DCC, if the back of the wheels touch the back of the point blade it will short out with both.
Just get the back to back correct and it will never happen and you will have no need to modify the points.
Obviously as with DC you will need frog polarity switches on every 009 point as the blade to fixed rail connection is unreliable.
With DCC you will also need isolating fishplates on every frog and extra feeds in every siding. These are not needed in DC, but if you have already used electrofrog points on a DCC 00 you will already know this.

[Ian McAulay]

If your back to back is correct on all the wheel sets you will have no shorting issues.

That's really all I need to know! Thanks!

Ian

[Ian McAulay]

I'm reasonably well up on good wiring practice for DCC from 00 experience on a big layout I'm helping a friend build.

Even for DC, I always liked to have soldered droppers to absolutely every piece of track, which I think was (at best) regarded as an endearing eccentricity. I've also never really liked using points as section switches to control sidings, so I always preferred to have sidings separately wired with their own switches on the control panel, which does lead to a lot of wires and a lot of switches!

Ian

[B.Meldon]

I'm reasonably well up on good wiring practice for DCC from 00 experience on a big layout I'm helping a friend build.

Even for DC, I always liked to have soldered droppers to absolutely every piece of track, which I think was (at best) regarded as an endearing eccentricity. I've also never really liked using points as section switches to control sidings, so I always preferred to have sidings separately wired with their own switches on the control panel, which does lead to a lot of wires and a lot of switches!

Ian

In 009 in DC or DCC you will still need to fit frog polarity switches as the blade to fixed rail electrical connection in Peco 009 points is unreliable.

[Frank]

If your back to back is correct on all the wheel sets you will have no shorting issues.
In this regard it is the same with DC or DCC, if the back of the wheels touch the back of the point blade it will short out with both.

Brian is quite right here.  The difference between DC and DCC is not whether there will be a short but how the system responds.  With DC it will go un-noticed in the vast majority of cases as the controller will just ride through a momentary contact without any problems.   With DCC the system is much more sensitive and is very likely to shut down immediately to protect itself from the fault.

Frank

[duttonbay]

...
With DCC the system is much more sensitive and is very likely to shut down immediately to protect itself from the fault.
...

A DCC layout will also reset and recover from the fault.


Faults caused by shorting between the turnout blade and the stock rail are very rare in 009/H0e because the gap between them is rather large. Wheels with settings that could potentially short across this gap are unlikely to be able to pass through the frog of the turnout and the wagon or loco with the incorrect wheel set would derail anyway.

But a short on a DCC layout will shutdown all locos running in that power block. 

You are right, Peco turnouts in particular have such a large gap between the blade and stock rail that this type of short is never going to happen.  I used Peco points in a small number of spots on the Dutton Bay, and never bothered bonding stock rails to blades. I had no shorts with these.

However other turnouts (particularly HOn30 turnouts from the US) have much less clearance, and these were all bonded to thre stock rail. 

[duttonbay]

But a short on a DCC layout will shutdown all locos running in that power block. 

...

Just like a DC system ...

Yes, if all of your locos are running off a single controller. If you have independent control of your locos by use of cab-control or other block switching, then only the loco causing the short should be affected. At least that was the case when I was using DC control.  Perhaps due to the way my layout was wired, which had a separate transformer for each controller.

[duttonbay]

There is no difference between a DC and DCC system when shorts occur - all equipment powered from that controller (DC) or booster (DCC) will stop and neither is more 'fault tolerant' of a short. The slight difference is that a DCC system will react more quickly than most DC systems, however, DCC will also reset quicker than most DC systems.

Correct. And in DC layouts with section control, with (say) two trains each in their own section, each with their own controller, a short will only affect that train. DCC boosters typically control largish sections of track, so a short at one end of a station might stop a loco or two at the far end of the same section. With section (cab) control in DC, your controllers might be driving two trains in very close proximity, each in their own section, and a short won't affect the other.
And the "slight difference" in reaction time means that very brief short from a loco shorting against the back of the point blade will result in a DC loco perhaps moving through the short before the DC system shuts down.
No matter. Avoding shorts altogether is the answer to all of these things...

[B.Meldon]

I have worked and seen several 009 DCC layouts that have unalterted Peco 009 points.
My experiance of these and in fact on all DCC layouts is that the most common source of shorts is caused when going into a point when it is set the wrong way.
I can not recall a single time when a short was caused by the loco shorting across the gap between the stock rail and the point blade, because of poor back to back settings.
As mentioned above the clearance for this in the Peco 009 points is massive, any weelset set that narrow to gauge will stall in the frog checkrails.
In fact this will happen at wider gauges than would be needed to short out to the point blade.
Bacicaly it is just not going to happen in 009 when using Peco 009 points, so there is no need to modify the points.

That said as the blade to fixed rail electrical switching is unreliable in all Peco 009 points so I would recommend, and I always use, frog polarity switches on every point.