Quick Way to find a Short?

Connect the U terminal of the transformer to the track outside rails. Then make a wire jumper using a automotive turn signal bulb in the middle of the jumper, and connect the wire from the transformer A terminal to the center rail. When you turn the power on, the bulb will light showing that current is being drawn without anything on the track...a short somewhere. And no stress on the transformer. Here is the hard part...disconnect sections or devices until the bulb goes out to localize the problem area or short.

Since you have only one feed, start by removing those two wires from the track lockon. That will prove that the trouble is either in the wiring or the track. After that, it's unfortunately a case of isolating one half of the layout, then one half of that half, etc, until you find the area that is shorted.  There is a wiring method that I have advocated for years, for folks who have decided to use conventional wiring with just one (or a couple) feeds. That is to use insulating pins "as if" you were going to create many feeds. Put the insulating pins at logical places along the row, such as where sidings enter the main line, etc. Just tie the feeds together, and in the event that you encounter a short (as you have) you just disconnect the feeds one by one until you clear the fault.

 

I have been called to help isolate and locate shorts on large layouts, using a specialized test instrument  that is used by telephone cable splicers. It will pinpoint a short right down to the nearest inch.  Unfortunately it weighs 30 pounds and costs $1200, or I would be happy to send it to you or bring it over and find the short for you.  If you're within a half-hour of 11964, I'll be right over.

So are you saying that ALL the track must be disconnected and testes individually?

No, I said that you need to determine of it's the wiring TO the track, or the TRACK itself. After that, you need to isolate the track into two halves, then divide the bad half again into halves (quarters, in other words) and then keep doing that until you find the short. Use the test lamp method, or a meter, and that will prevent the transformer from being damaged.

 

Remember that to create two halves, you need to break the center rail at TWO locations, to create two separate sections.

 

Generally, one should test each piece of track before it's installed, and then test the layout periodically as the track is laid down. In that way, a defective section or mis-installed screw will show up before the whole mainline is installed.

With tubular track, check the points where the center rail is crimped to the metal ties.  One or more of the cardboard insulating patches might be missing, causing the center rail to short to the ties (and hence the outside rails).  This is a visual inspection you can do without taking anything apart.

 

You might get lucky and see the problem right away.

 

Good point, Bob. Nothing beats a first visual inspection. Go slowly and use a magnifying glass. Something might pop out at you, saving a lot of headache.

Can someone explain how to test a piece of track with a meter?

Use ohms setting and look for infinite ohms when measured across center rail and outside rail.
Actually this is good, but it's possible that shorts may not occur until the track is attached or power turned on.

As my kids would say "OMG!".  I found it the old fashioned way with a magnifying glass.  And it should be noted that the bad track missing the middle track insulation was NOT the sixty some odd year track but that of a more recent vintage!

To clarify what cjack stated, when using a multimeter.  Set the meter to the ohms scale, touch the black lead to the outer rail, and touch the red lead to the center rail.  This is with the transformer disconnected from the track!!  If you get a reading, where the needle deflects toward the (right side of analog meter) indicating an ohms reading, you have a short.  If using a digital meter, it should give you a number reading, hence a short.  If the short is in the track, the proceed with APBloom's method by pulling the loop apart to make two halves.  Then repeat the first procedure with the test leads.  If it is shorted in one of the halves, split that in half again, until you narrow it down to the bad piece.  That's the simple way to explain it.

 

edited to highlight my original post.

One thing Teledoc forgot to add...disconnect the transformer leads when using the meter on the track. This eliminates any sneak paths back to the transformer.

I think the Arthur Bloom's method of "isolating one half of the layout, then one half of that half, etc, until you find the area that is shorted" is the way to go.

 

Crawling around with a magnifying glass won't do any good if there's a tear in one of the paper insulators and the bottom of the center rail is grounding out in a place that's invisible until you take it all apart.  Been there, done that...

 

Even if you have 100 sections of track in your loop, your worst case scenario using Arthur's suggestion is six or seven tries to find the bad piece (i.e., check 50 pieces, then 25 pieces, then 12 pieces, then 6, then 3, then you're down to 2).  

 

FWIW, in computing, such a search is known as a binary search and it is the most efficient type of search.

 

Steven J. Serenska

 

In computing, maybe, but the most efficient in this case would be to use thermal imaging.  Just one look would have shown this short.

I wonder if you put an amount of power without stressing the transformer into a shorted layout, that you could generally locate the short with an IR thermometer...

like the inexpensive ones at Harbor Freight?

You are correct, I should have said that it is the most efficient way to search if you have no other tools on hand.

BTW, how much did you pay for your thermal imager?

 

SJS

You can often feel the hotspot quite readily if you run several amps to the circuit for a spell. Thermal imaging would be ideal, at a cost of course, but not necessary for heat detection.