Our "problem" ended up a year later with a cooker fault to the earth in the commercial kitchen, earthing through the best line of earth it could get....
our camera tower! Buried 1m in the earth, it became the focus of a 240v cookers lust down the 3pin plug of the monitor. Then it went to the earth sleeve of the coax to the DVR, then to the cat5, to the cameras, which where firmly bolted to the tower.
It melted all the cat5e, the baluns, the cameras were all shot once the baluns melted and applied 240v to the BNC output, the DVR case was humming even though it ran on 12v psu.
Only the monit