I used to travel around the US as a field tech for a certain Global ISP that offered a unified network crossing oceans; I was at one of their sites one day and the site manager gave me the nickel tour. I saw this PDU and asked about the 1/8" inch wide notch in the 1/4" thick copper plate.

He explained that a contractor named "sparky" was using an non-insulated nut driver on the live panel and shorted the -48 VDC to the ground plane in front of it. The resulting arc blew the driver through the wall 30 behind it (the contractor stopped at the wall) and blew the upstream breaker.

When my eyes returned to normal, the site manager added that said contractor is not allowed on site anymore.