05-16-2009, 07:37 AM
Unfortunately, when you have eliminated all but the obvious, you have your cause.
Since the layout did not short before the work, and still shorts after the new work is removed, something has to have changed. Back when Kadee coupler height gauges were made of metal, I accidentally left one at the end of a spur where I had been testing cars. It took me 3 hours to find that short circuit. Chances are you either have uninsulated wires of opposite polarity touching somewhere, or there is something bridging the rails somewhere.
A short circuit is a short circuit in DC, AC, and DCC. The short circuit doesn't care about your power source. Switching power sources merely proved that the DCC system is identifying short circuits correctly.
If you use stranded wire (you didn't say which you use), it could be a very short piece of a single strand bridging 2 rails of a turnout. At adjacent screw terminals, a strand of a wire can go astray and touch the other terminal, even though all but the one strand are correctly connected. Of course, solid wire has its flaws, too. It can be easily nicked and eventually broken, causing a difficult to find open circuit down the road. But I digress. Another possibility are bus wires accidentally touching where you have joined feeder wires. You didn't say how you were attaching feeders to power bus wires.
Recommended trouble-shooting sequence:
1) Remove all cars and engines from the layout. A derailed car with metal wheels somewhere on the layout could be the cause.
2) Vacuum all the track. Sometimes brushing moves that invisible single strand, but doesn't get rid of it. Then check the track carefully with a bright work light.
3) A multimeter is advisable for this step. Set it to ohms and calibrate by touching the leads and making sure you read 0 ohms. Remove all power supplies by disconnecting their hookup wires. Measure resistance across the track. If it is still zero, then start removing feeders one at a time until your resistance measurement is infinite. The last feeder removed is the one that caused the problem.
4) If you are down to one pair of feeders left, and the track still has zero resistance, then it could be the feeders or uninsulated parts of the bus wires are touching somewhere. Remove the last set of feeders and now measure resistance between your bus wires. If you still have zero resistance, then the bus wires are touching somewhere.
In cases like this, there is something to be said for having the layout and power bus broken into isolated sections. Then the short can be isolated to a particular section, and finding it won't take as long.
Hope this helps
Fred Wright
Since the layout did not short before the work, and still shorts after the new work is removed, something has to have changed. Back when Kadee coupler height gauges were made of metal, I accidentally left one at the end of a spur where I had been testing cars. It took me 3 hours to find that short circuit. Chances are you either have uninsulated wires of opposite polarity touching somewhere, or there is something bridging the rails somewhere.
A short circuit is a short circuit in DC, AC, and DCC. The short circuit doesn't care about your power source. Switching power sources merely proved that the DCC system is identifying short circuits correctly.
If you use stranded wire (you didn't say which you use), it could be a very short piece of a single strand bridging 2 rails of a turnout. At adjacent screw terminals, a strand of a wire can go astray and touch the other terminal, even though all but the one strand are correctly connected. Of course, solid wire has its flaws, too. It can be easily nicked and eventually broken, causing a difficult to find open circuit down the road. But I digress. Another possibility are bus wires accidentally touching where you have joined feeder wires. You didn't say how you were attaching feeders to power bus wires.
Recommended trouble-shooting sequence:
1) Remove all cars and engines from the layout. A derailed car with metal wheels somewhere on the layout could be the cause.
2) Vacuum all the track. Sometimes brushing moves that invisible single strand, but doesn't get rid of it. Then check the track carefully with a bright work light.
3) A multimeter is advisable for this step. Set it to ohms and calibrate by touching the leads and making sure you read 0 ohms. Remove all power supplies by disconnecting their hookup wires. Measure resistance across the track. If it is still zero, then start removing feeders one at a time until your resistance measurement is infinite. The last feeder removed is the one that caused the problem.
4) If you are down to one pair of feeders left, and the track still has zero resistance, then it could be the feeders or uninsulated parts of the bus wires are touching somewhere. Remove the last set of feeders and now measure resistance between your bus wires. If you still have zero resistance, then the bus wires are touching somewhere.
In cases like this, there is something to be said for having the layout and power bus broken into isolated sections. Then the short can be isolated to a particular section, and finding it won't take as long.
Hope this helps
Fred Wright