I have a fairly large layout run by a CS3+. Recently I had to replace my main bus under the table as the CS3 was giving me that a short existing somewhere on the main line. I reconnected the first feed and everything worked fine. When I connected the second feed no matter where it was, my CS3 reset itself. When I removed the second feed all was fine again. Has anyone else encountered this problem?

Get a multi-meter and start checking dc voltage from the closest to the CS3 and out. If the voltage changes polarity you have reversed the wires. I am assuming you have three rail.

Hi Boris
You know by now that your CS3 has NO problems and that you have a short circuit on the second feed

Here is the process to locate where the problem is:

1. remove all rolling stock from your layout and check if the short is still there
   
2. break the faulty zone into smaller zones tryng to detect when the short appear while adding a new set of tracks
   
3. investigate the small zone causing the short on continue until the one track level
   
4. the result may be obvious or very unconspicuous. E.g. in M track a switch point spring burnt by a short and extended to the stud line. Another example is the result of using a dremel disk producing fine and invisible metal dust making the short, a forgotten tool on a track
   

Cheers
Jean