Ground loops

[Shteveo 0]

I have an install at big machine shop with 11 fixed cams and 7 PTZs with massive rolling and tearing on several of the PTZs. They were being powered by a fused Altronix power box. When I was unhooking them individually to move them to isolated power supplies, I disconnected the positive lead for one of the PTZs from the screw terminal in the power box and the camera stayed on! This happened with like 3 or 4 of the cameras. What could be happening to make this possible?

 

Geovision 1120 card in a custom PC

Costar PTZs

[survtech 0]

We've had similar problems when one lead of the power cable got shorted to ground. That usually happens during construction or remodeling when they crimp a power cable between the drywall and a metal framing stud.

 

One way to test for this: disconnect both leads at the power supply and run a continuity check between each wire and a known good earth ground (cold water pipe, grounded electrical box, etc.). If there is continuity, disconnect the other end of the cable at the camera and test continuity between the wires and ground again.

 

If continuity to ground is still there, you have a wire crimped or frayed and touching ground. That often can play havoc with multiple cameras that are powered by a common power supply. It usually affects the negative wire but can affect either.

[Shteveo 0]

This a brand new install. But the PTZs are in metal housings mounted to the ceiling joists. That is usually where we see loops coming from. The strange this is that in initial install three weeks ago, the cameras were all messed up, ground loop isolators where installed and everything got better. Then a week after that they started rolling and tearing again. I can't see what changed to cause the loops to come back, as it were.

[survtech 0]

Ground loop isolators typically can't overcome real serious loop issues. You may have to isolate every camera using nylon screws, washers, etc.