WS-12-250-AC first power connect something blows up

[tma]

Thank you Gerry for analysis and reporting back. I'm sure there's no temp difference between my office and the lab - it's just next doors and doors are always open. I'm also sure we didn't drop anything into the two switches, they had just been unpacked, but I'd agree it has been something that shortened one of the power lines to ground, but not between the power lines. The PCB layout would tell if there's any possibility for that.

Both switches are in production now and are working just fine. The next one that we tested didn't spark. If we ever see this happen again, we will take the switch apart to have a better look at (and take pictures from) the mains input area on the power supply. If you want me to, I will get the first switch back to the lab, though.

Again, many thanks, Thomas.