# Why is this causing a short?



## tkruger (Jan 18, 2009)

To enter the outside mainline from my roundhouse the locomotive must cross the inner line. Currently I have no power to the inner line. The locomotive shorts out when it hits the pair of insulators between the roundhouse area and the track area (circled in image). It will run fine once on either side of these gaps. Any ideas? This all worked fine when this was DC.


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## Lemonhawk (Sep 24, 2013)

Most likely the rail polarity changed on the other side of the insulated joint. If you have a dcc tester it would lite when clipped across one of the insulators. Check your wiring to make sure the same wire that powers the right rail on one side is the same wire that is powering the right rail on the other side.


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## Cycleops (Dec 6, 2014)

Are you sure it shorts or is it just stopping? As I see it if you have insulated joiners at that point you would have no power as the crossing has all dead frogs.


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## Brakeman Jake (Mar 8, 2009)

1)First,DCC is much more sensitive to momentary shorts than DC so even the slightest problem that didn't show before may be much important now.

2)Then,if the layout was wired using "common rail",wich is typical of DC,this would mean that the inner line is still 50% alive even if power is turned off to it.

3)The picture shows a rather steep curve coming from the turntable wich tells me that some wheels (in particular six axle locos)may be tracking a bit too far inside and be touching one (or more) of the crossing's inside tracks,thus shorting.

It's my guess that the wiring isn't the problem.I believe it's only a track gap problem.I'd try filing the ends of the crossing's internal rails so that the inside of the wheels can't reach them.Not much,just a few thousands of an inch should do it.


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## tkruger (Jan 18, 2009)

I have my doubts on the polarity since it worked with DC and the wiring did not change other than to swap the transformer over. 

There is an r18 into the roundhouse, small turn table small locos only not an issue with that.

Yes there is power on each side since the engine works on both sides.

I will try the filing as the brief touching of the track rail does make sense.


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## DonR (Oct 18, 2012)

Do you have insulators in both rails at the crossing?
Or, as Jake brought up, are you using commong rail,
with an insulator in only one rail at the crossing.

Does the track from the crossing to the turntable
take power from the turntable? Does the turntable automatically
match polarity?

You can test 'phase' (polarity) with a meter set to AC volts.
Put one probe on the left rail ON the crossing, put
the other probe on the left rail beyond the insulated
joiners. If you see a voltage of 14 or so the turntable track
is out of phase, thus the short. 

Consider: the crossing is on the mainline phase.
the turntable track is on an opposite phase.
the system shorts when the loco wheels span
the insulators, but when completely either
side of the crossing it runs. It's DCC, so once
the short (loco wheels vs insulators) is cleared
it will run on the turntable track or any track.

I believe you have a phasing problem; the main vs the turntable track.
I'd suggest the turntable track is taking current from the turntable.
Change the turntable track feed from the turntable to the main buss.

Don


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## tkruger (Jan 18, 2009)

There are insulators on both rails. The track on both sides take power from the same source. This is what confuses me. When both were DC I could drive off this no issue for years, positive to one rail and negative to the other. I would think the phase would not change just by going to DCC, can it? 

There is one DPDT switch that the power goes through on its way the the turn table. This is to kill it for maintenance etc. Power only reaches this area when this is on, it gets its power from the main, same as the main line does.

There is allot of wiring that went into setting this up for DC. In one other yard I found a short caused by a rotary switch used to select the siding. This worked great in DC without any sign of an issue. I am starting to wonder if one of the components I used in the round house area is doing something funny.


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## tkruger (Jan 18, 2009)

Just had a bad thought. I have an Atlas turn table. It changes the polarity as it turns on the table only. Could this be an issue going forward? If so and I have to rip that out I may have to re-wire this anyways.


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## mesenteria (Oct 29, 2015)

If you had that conflict, it would short right where the first metal tire makes contact with your radial into the bay after coming off the turntable, or else it would cause a conflict and a short leaving the turntable on the other side of the bridge and entering the lead out to the yard. If there was no such conflict in DC, it won't be a conflict in DCC.

There is a problem with conflict of phase on the crossing. You have jumpers under it, if I recall mine correctly, and they help short locos to get across. This suggests to me that opposite that crossing there is incompatible phase. IOW, you have one side wired the wrong way, or else you have fed the crossing itself and it is wrong in phase for the lead.


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## Brakeman Jake (Mar 8, 2009)

The Atlas turntable does change polarities as it rotates BUT only to the rotating bridge and will never change polarities to the tracks that go to/from it,so shouldn't have any effect on whatever happens at a crossing away from it.And switching to DCC shouldn't change anything...the turntable will still handle the DCC phases as it did with DC polarities.

I still stand behind what I've said earlier...wiring isn't the problem,if indeed nothing has been changed since the DCC swap,obviously.Keep in mind,there was no problem with DC.


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## DonR (Oct 18, 2012)

Jake

Did you do the phase test I suggested earlier? That is
the final answer. It seems obvious to me that some
how the phase of the track to the turntable is reverse
to the main. You might try to reverse the track 
drops on it. See if that solves the problem.

Don


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## Lemonhawk (Sep 24, 2013)

If you use a jumper cable across the rail insulator does it cause a short? I still think it's a phase issue that had a switch that took care of the problem when it was DC. As suggested above you could also see if there is any voltage across the rail insulator using a multimeter on the account setting. All these are easy tests that would give us more insite into the problem. I assume the rail was insulated for a reason, most likely so you could park a locomotive their. You did mention a dpdt switch which could have controlled direction besides shutting the block off. Just some more rambling ideas. To bad were not located near one another.


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## tkruger (Jan 18, 2009)

Thanks for all of the advice, unfortunately I have not had time to get back to the track last night. I will need to get the multi-meter etc out tonight and go from there.


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## tkruger (Jan 18, 2009)

Found the issue, well there was more than one. First the polarity was swapped. Only thing I can think of was that I changed a wire when I hooked up the DCC and removed the DC feed. Next issue was, as stated before, had to do with the crossover. When crossing the first rail of the inner track the wheels briefly hit. Apparently I never saw this in DC since they just coasted over the spot.

Thanks for everything.


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## Lemonhawk (Sep 24, 2013)

Glad you found it!


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## DonR (Oct 18, 2012)

I had that momentary short on some of my Peco Insulfrogs, a wide
tread on a wheel can short where the two rails are close. I use
a tiny drop of clear finger nail polish at the point where it occurs.
Problem solved for a while, then dab again.

Don


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## Lemonhawk (Sep 24, 2013)

Having worked in aerospace I would like to say there is just one fault. That's the theory but in practice it's usually more and solving one just gets you to the next. Your persistence has paid off tkruger! On to the next.


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