One of my customers installed 3 PC's to run a taxi booking/dispatch system. They decided to do things properly, so they got an electrician to install an independent ring with sockets for the computers, the screens, printer, router, radio TNC, and some spare sockets. The ring was run off a smallish UPS.
So far so good.
Since the ups would only provide a short duration in the event of a power failure they bought a small generator, so if mains went, the ups would take over for long enough for them to get the generator out of the cupboard and connect it to the input of the ups.
Seemed very good.
Some years later a digger in the street severed the mains. Remember those 'spare' sockets.... two electric heaters and a kettle had found their way onto the circuit so the UPS threw a tantrum. They couldn't find the key for the cupboard containing the generator. The fuel in the generator was several years old and no-one new where the starting instructions were. An arguing mob of irate drivers soon had sore arms from pulling on the starter handle. then some bright spark noticed that the shop two doors away had power. And they had a long extension lead. Soon they had a working computer, screen, router, and TNC.
Now an even brighter spark reasoned that if they removed the socket from the extension lead and replaced it with a plug, and plugged that into one of their wall sockets, it would power their 'ups' ring and all their computers would work. I suspect that their degree of familiarity with H&S laws was about as advanced as their knowledge of three phase mains distribution (yes the shop down the road was on a different phase)...