A client of mine had a server rack that needed a 15 Amp circuit to power their UPS because the server kept going down. An electrician was hired to run a new circuit.
After the work was completed, I commissioned the UPS and all was well .. until someone boiled the kettle at which point the UPS would start screaming and the kettle would stop working.
After crawling into the basement I discovered that the extra 15 Amp circuit was nothing more than a twin flex connected to the kitchen circuit.
The client was unimpressed and if I recall correctly, 20 years or so ago, the electrician lost their licence.