Quick Way to find AC Electrical Short

You might try to disconnect the bad loop from power and measure along the track with a low resistance scale ohmmeter. When you get to the short, the ohms should be at the lowest reading that you experience.

Or...after it's been on, maybe feel along the track for a warmer spot. Careful though!

I would use a vom meter and set it to ohms, disconnect the track  power connecter where the power is fed from. when you sure you disconnected use the ohm meter  to check if there is a direct short from center rail to outer rail or some low ohm value 6 ohms 4 ohms etc. , you should not have a direct short or your breaker will trip! I'll bet  you find no short then check from center rail to center rail around your layout I'm guessing you find some  resistance higher ohms maybe even complete open or even a higher resistance. if you do I would suspect you have a poor connection between center rail to center rail causing this issue I have seen it before on older layouts  especially if there in a damp basement !if you find this issue you don't have to dismantle your layout to replace the pins you can install jumpers from one rail to the next and solder on the side of one rail to the next. a lot of time corrosion sets in inside where the track pin goes between the pin and the inside of the track. this is the easiest fix I know you can do and not have to tear your layout apart to get it working again!

p.s. let us all know how you  make out and good lluck!\

Alan

Many consumer grade VOM's aren't going to be sensitive enough to easily show the change in resistance as you approach the short.  You may have to do the old "Divide and Conquer" - split the loop in half and see which side has the short.  Split in half again and repeat.  Keep repeating the process until you find the problem...

Are you sure it's a short and not a bad or failed connection?

Look for heat on your center rail. I had the same issue and a light and intermittent short was present at a center rail insulator.  Heat was what revealed it to my fingers.   A meter couldn't bridge the short to read it, not enough voltage.  I.e. there was a gap that the ac  voltage could jump, but not the meter.

Since it's not blowing your breaker, I would agree with RJR and Adriatic above, poor or loose connection(s) somewhere. 

Also the divide and conquer method, although it can be a real pain and time consuming, works pretty well. Unfortunately, the solution to the problem is ALWAYS found in the LAST place you look!  

Here's a trick I've used on old strings of Christmas lights. If you've got a wireless phone (the kind with a base unit and an antenna), use the handset to look for radio interference. You'll have to have power to your track to do this. If there is sparking somewhere, the handset will pick it up. Of course you need to turn on the phone to pick up the dial tone. Listen carefully for static noise. It should be more noticeable near the problem area.

A cheap walkie-talkie set would probably work in the same way; I haven't tried that.

It all depends on what kind of problem it is. I was able to locate bad sockets and bulbs in the string of Christmas lights without having to check each socket.

What brand of track? It doesn't sound like a bad connection. With no load a poor connection usually won't show a voltage drop until a load is applied.

John, Its a mixture of Atlas and Gargraves track, The switches are a mix of Atlas and Ross

Ok. That rules out metal ties. Do you get a spark when you disconnect that loop? Your best bet is the suggestion of others. Split the track until you find the problem section. It sounds like you don't have any blocks, which makes it a little harder. If you are absolutely sure there is nothing on the track, you might start with the switches. Are they motorized?

A friend had a short and took everything off the track...except he forgot about a siding with a switcher on it which was slightly ajar. And another friend had a short on half his layout which ended up being another issue of a siding with a passenger car ajar.

Just sayin'

I agree, likely switches if it's wood ties. Check for debris near the point rails of course.  A single loose wire strand broken off and landing in the wrong spot sounds very plausible as a foriegn cause.  Try working the switches to move debris and then leaving them in the opposing position. One by one so you know which needs attention. Don't group fix attempts or you won't know what you did right. Process of elimination takes diligence.

If the track is ballasted, or attached in way that would be a pita to remove, consider cutting the center rails via dremel to create a block for each switch.  Reconnecting the blocks by wire afterwards if everything checks out ok.

The "Lemonade": Should anything like this happen again, it will be much easier to check quickly if each switch is on it's own block. 

Using terminal blocks vs splices in layout design also helps with speeding diagnostics like this. Few folk like to think about that though. If they aren't there, you may want to add some while doing this.

The Z4 flashing but not tripping tells me it's very light short, the Z4 likely thinks it's just a heavy loco draw (a single wire strand could do this). As mentioned, it may not be readable by ohms. It's no gaurantee that you can find it by voltage drop either, but testing with low voltage and slowly increasing it slightly as you test may help.

I don't know where he got it or who made it, but a pals dad, now passed, had an automotive short detector that could find even partially damaged wire inside insulation. It was as simple as grounding it and passing the tip along a wire.  I will call later to ask more, but the son has strange work hours, and might not call back until Sat. (I want to know more anyhow, he passed a few days after I saw it used.) It likely uses induction or a special circuit to perform Leo's phone static trick (which is pretty cool , right up there with seeing IR light with a digital camera/phone )

dkdkrd posted:

cjack posted:

Or...after it's been on, maybe feel along the track for a warmer spot. Careful though!

Or simply wait for the smoke to curl upwards. 

THERE'S the problem!!

.....just kidding, of course!

LOL!, did that one time in my younger days!  Automotive related, not train related.  Kept blowing a fuse once or twice a month.  Several weeks of exhaustive searching and testing produced no results.  Finally gave up in disgust and replaced the fuse with a short piece of brass tubing.  Figured I'd find that intermittent short one way or another.  And one day about a week later, yeah I did find it!  Took off down the street, and all of a sudden smoke started coming out from under the hood!  Yanked the brass tube quick-like, pulled over, and checked under the hood.  Finally found the culprit - a single wire had cut through the insulation and would short out on a sharp metal edge of the inner fender well (probably if I hit a fairly big bump while driving).  Smoked the wire of course, had to replace about 3 feet of it.

The moral of this story?  Never let teenagers look for electrical shorts.  They'll find 'em!!! 

It's too late to help the OP, but this highlights one of the reasons I suggest that, when designing a layout, one use many toggle-switched blocks.  Not only does this give added operational flexibility especially when running conventional, but it permits one to isolate shorts to a small area.  Also, you can keep the layout operating except for the shorted area.

On my layout, every track switch marks the end of 3 blocks; I sever any under-switch interconnections.

Mixed Freight posted:

dkdkrd posted:

cjack posted:

Or...after it's been on, maybe feel along the track for a warmer spot. Careful though!

Or simply wait for the smoke to curl upwards. 

THERE'S the problem!!

.....just kidding, of course!

LOL!, did that one time in my younger days!  Automotive related, not train related.  Kept blowing a fuse once or twice a month.  Several weeks of exhaustive searching and testing produced no results.  Finally gave up in disgust and replaced the fuse with a short piece of brass tubing.  Figured I'd find that intermittent short one way or another.  And one day about a week later, yeah I did find it!  Took off down the street, and all of a sudden smoke started coming out from under the hood!  Yanked the brass tube quick-like, pulled over, and checked under the hood.  Finally found the culprit - a single wire had cut through the insulation and would short out on a sharp metal edge of the inner fender well (probably if I hit a fairly big bump while driving).  Smoked the wire of course, had to replace about 3 feet of it.

The moral of this story?  Never let teenagers look for electrical shorts.  They'll find 'em!!! 

 

It’s better to replace the fuse with a turn signal bulb and flex all the wiring until the bulb lights. Less distructive.

Adriatic posted:

I agree, likely switches if it's wood ties. Check for debris near the point rails of course.  A single loose wire strand broken off and landing in the wrong spot sounds very plausible as a foriegn cause.  Try working the switches to move debris and then leaving them in the opposing position. One by one so you know which needs attention. Don't group fix attempts or you won't know what you did right. Process of elimination takes diligence.

If the track is ballasted, or attached in way that would be a pita to remove, consider cutting the center rails via dremel to create a block for each switch.  Reconnecting the blocks by wire afterwards if everything checks out ok.

The "Lemonade": Should anything like this happen again, it will be much easier to check quickly if each switch is on it's own block. 

Using terminal blocks vs splices in layout design also helps with speeding diagnostics like this. Few folk like to think about that though. If they aren't there, you may want to add some while doing this.

The Z4 flashing but not tripping tells me it's very light short, the Z4 likely thinks it's just a heavy loco draw (a single wire strand could do this). As mentioned, it may not be readable by ohms. It's no gaurantee that you can find it by voltage drop either, but testing with low voltage and slowly increasing it slightly as you test may help.

I don't know where he got it or who made it, but a pals dad, now passed, had an automotive short detector that could find even partially damaged wire inside insulation. It was as simple as grounding it and passing the tip along a wire.  I will call later to ask more, but the son has strange work hours, and might not call back until Sat. (I want to know more anyhow, he passed a few days after I saw it used.) It likely uses induction or a special circuit to perform Leo's phone static trick (which is pretty cool , right up there with seeing IR light with a digital camera/phone )

The probe senses a strong magnetic field caused by the short.

cjack posted:

Mixed Freight posted:

dkdkrd posted:

cjack posted:

Or...after it's been on, maybe feel along the track for a warmer spot. Careful though!

Or simply wait for the smoke to curl upwards. 

THERE'S the problem!!

.....just kidding, of course!

LOL!, did that one time in my younger days!  Automotive related, not train related.  Kept blowing a fuse once or twice a month.  Several weeks of exhaustive searching and testing produced no results.  Finally gave up in disgust and replaced the fuse with a short piece of brass tubing.  Figured I'd find that intermittent short one way or another.  And one day about a week later, yeah I did find it!  Took off down the street, and all of a sudden smoke started coming out from under the hood!  Yanked the brass tube quick-like, pulled over, and checked under the hood.  Finally found the culprit - a single wire had cut through the insulation and would short out on a sharp metal edge of the inner fender well (probably if I hit a fairly big bump while driving).  Smoked the wire of course, had to replace about 3 feet of it.

The moral of this story?  Never let teenagers look for electrical shorts.  They'll find 'em!!! 

 

It’s better to replace the fuse with a turn signal bulb and flex all the wiring until the bulb lights. Less distructive.

The circuit?  The dash panel lights and all the tail lights.  The short?  Ended up being a small marker light on the left FRONT fender.

In retrospect, I guarantee I'da NEVER, EVER found THAT problem, no matter what I did, outside of a complete new wiring harness (which would have cost ten times more than the vehicle was worth).  So even if the vehicle had totally burned up, at least I would have had the satisfaction of finally finding that elusive short!!! 

Still cannot find it and I really do not want to start slicing the track to find it. Could I set the voltage to a low setting on the transformer and using an Infrared heat probe look for a hot spot?