Company I worked for did building energy management systems. The wiring for sensors was twisted pair telephone type cable, multipair where possible. One building we were seeing random temperature readings, as if there was some sort of interference. Checking on site we found a spare pair had been punched down, a 13A plug attached and plugged into a mains socket. At the other side of the building the same pair was picked out from nearby marshalling box, and wired to power a radio.