Hello All, 
  
This is my first time posting and probably the only way I can figure this problem out. My company recently bought a new building and it has an existing CCTV system that was not hooked up. 
  
However, I am experiencing some problems to actually getting it back up and running. There are 2 central power supplies a 12VDC and a 24VAC. The 24VAC run the longest runs of about 400 feet and to the outside cameras. The 12VDC are the shortest and are only interior cameras. 
  
Problem: When one camera is powered on 2 other cameras also power on for some reason (the red positive are connected to the power supply on but the negative are disconnected). I cannot understand this for some reason. The cable that was run is Siamese 95% Copper Shielding RG59. When all cameras power on, numerous are unclear and staticy on the top left of the screen. Is this a ground loop problem? ALl BNC crimps are taped with electrical tape to prevent a ground loop on the steel framing.   
  
I also was wondering is it true that the DC cameras use the shielding in the RG59 and the (-) Black wire are connected inside the camera itself?  
  
I traced the wires back and fourth and they are not spliced anywhere or have any nails or anything through them. 
  
Edit: Let me clarify it. 
  
Line 1: Connected both + and - in Power suply 
Line 2: only + connected 
Line 3: Only + Connected. 
  
When Line 1 is powered on, both Line 2 and 3 also power on with the - disconnected