I took out a block of 20+ residential units with a cheap domestic level Potato Clock that had a built in block of domestic power outlets. I was tidying up our home office and thought that it would be a good idea to plug my mobile phone charger into the UPS to give me a spare power point above the desk. The charger was faulty - The resulting bang temporarily deafened me, tripped the house power board, blew the 50A fuse to the house, and took out the main circuit breaker for the site. Our electrical contractor fixed everything past the breaker in less than half an hour but we still had no electricity as the main breaker was dead. He called the power company. We had to wait for another 2 hours because the power company engineer did not have a spare breaker so he had to go back to base. I admitted what had happened, but I don’t think the engineer believed me until he saw what was left of the phone charger.