Something worth checking: When I was wiring my house, a couple of times when I pushed a switch or outlet back into the box after connecting it, the bare ground came into contact with the hot screw on the device. The tricky thing is, you can pull it out of the box and try the circuit and it works just fine because the device is pulled away from the part of the ground that is touching. Then, when you push it back, everything tends to go back where it was, and it shorts again. After a couple of episodes of this, I became more careful about watching where the ground goes when I push things back in the box.

This was all Romex. If you are using conduit, you might not have bare grounds. In that case, I'd check the hots for cut insulation where they enter the boxes.

Tell us the wire conenctions in the switch and the light. Was anything changed recently that caused this to start happening? switch? fixture?

This might be a case where you could put elecrical tape over the screws on the side of the receptical, especially if your metal boxes are the really small ones.

fa f320: good thought, however, the breaker trips even with all the wires hanging out of the box as I troubleshoot possible problems.

joed: this is all new work for a kitchen. the switch is connected with each black wire on the single-pole terminals. At the light, a simple ceramic fixture, black wire to brass, white to silver. grounds connected to metal ceiling box and with pigtail to metal switch box and grdng. screw on switch.

Another thought I had to try is to see if somehow a wire got damaged somewhere along the line.

Check your wire clamps on the NM cable. You may have one too tight that has pierced the insulation.

That would be my guess. A wire clamp too tight, a nail or screw into the cable. You need to separate the circuit by splitting some of your conenctions and testing for a short, hot to ground or hot to neutral.

Something else to check - while uncommon - is a bad run of cable. Once I was moving some boxes in my attic, and bumped into a run of romex (new wire, about 6 months old) the lights dimmed for a couple seconds then went back to normal. Didn't think twice about it, until I discovered some things weren't working and a breaker was tripped. Did some troubleshooting, and found the section of wire that I bumped had about 18 inches of incomplete insulation on the black wire, and when it got moved, the bare part of the black wire touched the fround wire and caused the short. Sounds like either a cable clamp too tight, as has been suggested, or a nail or screw through the wire, or a bad run of wire. Let us know what you find.

The mystery is solved - by process of elimination I finally figured out that the wire to the light had mashed insulation exposing the wire at the box - such a small spot! Clipped it out and now I'm good to go! Thanks for all your thoughts...happy wiring