There had been electricians from Timm Electric doing infra-red testing of the PDU systems, which is standard maintenance and we had been informed there was no risk of an outage, thus it didn't need to be scheduled during a maintenance window, etc. They have admitted to an error on their part which seems to have caused a reduction in voltage for a short period of time over a relatively small section of our data center space. This reduced voltage seems to have caused some systems to reboot, while most did not, and none of our network equipment rebooted during this incident.