CCTV Ground Loop or other voltage issue?

[wick1144retired]

I am upgrading a DVR at a 5 story office building. Cameras are located and powered locally at each floor and video cable is run to DVR. All cameras were working with old DVR. I installed a new DVR, HDTVI compatible. Now only those cameras that are in close physical proximity show video. So I checked voltage between camera coax cable shielding coming from the camera and ground @ DVR. DC 0 volts, AC 32-33 volts on only the cameras that are not now working. 4 of the cameras that are close to the DVR are working. I don't want to run power cable from DVR location to each cameras location if possible. Is this a ground loop issue or other voltage issue?

 

[petersonra]

I am upgrading a DVR at a 5 story office building. Cameras are located and powered locally at each floor and video cable is run to DVR. All cameras were working with old DVR. I installed a new DVR, HDTVI compatible. Now only those cameras that are in close physical proximity show video. So I checked voltage between camera coax cable shielding coming from the camera and ground @ DVR. DC 0 volts, AC 32-33 volts on only the cameras that are not now working. 4 of the cameras that are close to the DVR are working. I don't want to run power cable from DVR location to each cameras location if possible. Is this a ground loop issue or other voltage issue?

Is it possible that the signal is just degrading over distance? You can buy modules to send the video signal farther via ethernet wiring.

 

[hbiss]

With 32-33 VAC to ground at the end of the coax at the DVR you do have a ground potential difference. It might be that the old DVR could tolerate it but the new one won't. They do make isolaters for this problem. They pass video but not the voltage. You would need one per input though I kinda think they make a bank of them in one enclosure. ADI should be able to help you out.

-Hal

 

[wick1144retired]

The distance is fairly short. None are more than 200'. I'm more concerned with reading 32-33VAC between camera cable shielding and DVR location ground only on the cameras that are not working.

 

[wick1144retired]

Ground loop isolators. I've tried one with no luck. It just seems like that is a lot of voltage. I've had other ground loop issues in the past, but that was reading DC voltage, not AC.

 

[petersonra]

With 32-33 VAC to ground at the end of the coax at the DVR you do have a ground potential difference. It might be that the old DVR could tolerate it but the new one won't. They do make isolaters for this problem. They pass video but not the voltage. You would need one per input though I kinda think they make a bank of them in one enclosure. ADI should be able to help you out.

-Hal

if he is reading this with a digital meter it might not mean anything though.

 

[JFletcher]

There is a far greater chance that the BNC connectors on the rg59 were not installed correctly, and you when you remove them from the old DVR and put them onto the new, you created a problem with the signal. I would reterminate both ends of the cables to the cameras that do not work before thinking about ground loops, wiring problems, DVR / camera compatibility issues, etcetera. BNC connectors are extremely easy to mess up, the closer cameras may have messed up connections to, however due to the distance of the cable, the camera still work. If you think it is a ground Loop causing the problems, unplug the cameras locally from their power source, and bypass the ground... Just to test them...

The cable is rg59 correct? RG6 will not work (well) with camera systems, the impedance is different from rg59, 75 versus 50 ohm

 

[wick1144retired]

With this issue occurring on 12 out of 16 cameras, I tend to think the BNC connectors would not have failed on that many cameras at the same time. I did check voltage with a digital meter. With only the cameras reading that voltage are failing, I find it hard to believe that it is not part of the problem. I could be wrong, that's why I'm looking for additional thoughts. Thanks.

 

[wick1144retired]

RG59 95% shield. It is proper CCTV coax.

 

[hbiss]

The cable is rg59 correct? RG6 will not work (well) with camera systems, the impedance is different from rg59, 75 versus 50 ohm

No, RG6 is 75 ohm also. True RG6 with the solid copper center conductor and copper braid is fine, the problem comes in when you try to use the CATV cables that have aluminum braid and foil for the shield and a copperweld center conductor. If you use it for powering the cameras it could be a problem.

@wick1144retired, I agree with you that you have a problem with different ground potentials assuming you are measuring it properly. (Really shouldn't call it a ground loop).

You are going to have to find out where this is coming from. If you disconnect power to one of the offending cameras what happens to the voltage? Is the camera grounded through the power supply? If so, how about temporarily lifting the ground at the receptacle to see what happens to that voltage? Is the camera mounted to a conductive grounded surface and if so, what happens to the voltage if you temporarily remove it and let it hang there?

I've had other ground loop issues in the past, but that was reading DC voltage, not AC.

I would like to know how you could be seeing a DC voltage.

-Hal

 

[wick1144retired]

In the past case, it was caused by the power supply (plug in type transformer)

 

[zbang]

Ground loop isolators. I've tried one with no luck. It just seems like that is a lot of voltage. I've had other ground loop issues in the past, but that was reading DC voltage, not AC.

I'm going to guess that the old system isolated the feeds and the new one doesn't. In that case, you need to isolate all of the cameras. Have you tried just one camera with the isolator?

It's possible that one or more of the power supplies has a problem. Anyway, divide and conquer- try one camera at a time, check the power supply outputs to see if they're all correct (and floating from chassis ground), move one PS to another camera, etc.

It's also possible that there are a couple of cable faults out there, check to see that the shields are really isolated when disconnected from both ends. Unfortunately, I think there's going to be a lot of running around disconnecting things and testing them.

 

[GrayHair]

zbang pretty much has it. Newer equipment is almost always more sensitive, explaining why there were no problems with the old DVR. Connect one camera at a time looking for indications of a ground loop. Isolation transformers is the way to go. N transformers will be a BUNCH cheaper than N*2 fiber modules.

 

[wick1144retired]

Well, to make a long story short, I eliminated the voltage by running power from the head end to the cameras, putting everything on the same circuit. As far as the cameras go, I had to replace the cameras. Now everything is fine. I am curious if the voltage on the video cable caused the cameras to fail. Thanks for your thoughts.