Most efficient way to find a short circuit in a buss line

After adding some additional scenery to the layout making some other modifications when I turned on the PowerHouse the red light on the TMCC Direct Lockon turned red, meaning a short circuit.  

I would retrace my steps from there if all was fine till you did the above …….

Pat

1. Is the bus wire a straight line, logically, or a loop?

2. Do you have a "return" bus (so-called "ground") bus, that all the accessories are attached to?

3. How long is the bus wire?

4. Can you cut it in half, and see if the short goes away?

5. Using the "cut in half" method, cut the bad half in half again. Soon you will have narrowed the problem down to a few feet of wire.

All the above can be done without the meter.

Thank you for your reply. The buss line is a loop. The loop is approximately 16” in diameter and only provides power to lighting and limited accessories that need constant power.

How are you bringing the ground to the accessories? I suspect that a piece of scenery is shorting between the ground and the hot side of an accessory. One question, I am not familiar wth the powerhouse, are you saying that the powerhouse plugs into the lockon, then the buss loop starts/ends on the hot connection on the lockon? Is the lockon connected to the track? Or are you just using the lockon as a means to get power to the buss? If it is connected to the track and you were doing scenery, look for something that could potentially be shorting the rails as well.

I am not sure what is meant by bringing the ground to the accessories?  I have two wires in a loop. Both the positive and negative wires are connected to the TMCC lockon (the little square box at left in picture). The AC current from the PowerHouse is plugged into the TMCC lockon. No tracks are being powered by the TMCC lockon and this particular PowrHouse.

Note:   Arthur P. Bloom post above. 

Okay, now I understand , to the lockon is basically being used as an adaptor to allow the powermaster to power the accessories. So basically you have the positive buss (that I assume does not come back to the lockon, you don't need to) and there is the negative (ground) buss (When people say ground, it is the same thing as negative in terms of what you are doing, it is also known as the return).

One simple test to get old Occam out the way, if you disconnect the buss wires from the lockon, and power up the power master, is it okay? It is possible the lockon itself is shorted, and it is an easy first test.

Other than thatt The simplest thing I would do is look at the scenery you have done, and see if any of it is on or around a powered accessory. My guess is in doing the scenery you shorted the positive and negative connections at one of them, something conductive in the scenery material shorting out the two sides. Instead of trying to isolate the buss segments, as Arthur suggested, if you can easily disconnect a lead to each accessory, do that, put power on, and see if the short goes away one at a time.

If that works, then there is something with the accessory. If you can't easily disconnect the accessory (for example, on a coal loader taking the wire off the binding post they use),  cutting the feeder to the accessory (either side) may be simpler than cutting the buss. Cut the feeder, and same thing, apply power and see if the short is still there, reconnect, repeat with next accessory until you find the one doing it (you may want to reconnect the feed after each test, if you go through the whole range of accessories and the short still happens, it means it is upstream someplace). If you find the accessory with the problem, then check and see if scenery material could be doing it. Check the feed wire, make sure for example that the hot wire is not touching the accessory if it has a metal base (like a gateman, for example), that would be a dead short. Other  trouble shooting, like if it is motorized, the engine has seized (another example of scenery, piece of something gets into the motor drive), the feeder had exposed wire where it shouldn't, something conductive shorts the positive/powered side to the body of the accessory (which is likely a dead short to ground, since ground terminals tend not to be insulated from the body of the accessory in all cases).

If disconnecting the accessories one at a time doesn't pinpoint the problem, then you need to look at the buss wiring. One possibility, if you soldered in your drops, could the positive and negative buss drop wires be shorting to each other, if the solder joint is exposed and they are touching (it happens).

just how many things are connected here? Have you added up all the power draw?

Thank you for your very detailed explanation and comments. The short kept me awake most of night trying to retrace my steps from the last time it worked up until the short. I remembered that the top portion of the MTH yard tower had separated from the base and the wires for the tower lamp were under some stress as the tower hung only held together by the wires. When I disconnected the tower from the buss wire and restarted the lockon, I received a green light indicating no short. Following a few minor adjustments to the yard tower and reconnection to the buss line, everything worked fine.