Last job I was on there was a strange deal.

I'll break down the facts:

Lighting ckt:#31
Power:#6

I was working on the lighting so I went to the panel to turn off ckt 31. I went back the the jb with ckt 31 and it was off.

Then, another electrician had to turn it on during lunchtime for these bigwigs having a meeting in a room on CKt 31. I came back after lunch and noticed that it was tripped.

Here is what is wierd. When I reset ckt 31, it tripped along with ckt 6 (power) . I did not do the roughf in . But, what could possible cause this. The GF did not have any clue either. He took over the job half way through.

Both ckts are in the same panel 6 and 31. Any ideas? Even if there is a ground fault on the lighting circuit I was working on , how would 6 trip as well?