Joe calls from the county jail, he just finished installing 16 cameras for the jail and now that he has all the cameras up on the monitor there are small lines running through the screen on each camera. His first thought is that there is defective equipment. Either the CCTV cameras or the DVR are bad. Neither are bad, the culprit here is video ground loop interference.
I will spare you the science of a ground loop (which looks like this)…
Just know that they cause horizontal lines in the video monitor.
This can be caused by many different factors and tracing the issue can be a pain. One cause is running your security camera cable over a high power source. This can also be caused by load unbalance when high power is shut on and off. To avoid this, make sure to run camera wires away from power lines (a minimum of 12 inches) if possible and especially not directly on top of them.
If you are using 24vac power transformer and you have this problem you can reverse the wire on the power supply to get the bad signal to go away. This is an old trick that some of the Veteran CCTV installers use (let us know if you’re looking to become a CCTV installer).
Another issue with ground loops are metal buildings. There are times when customers mount cameras to the side of a metal building and the entire building is one large conductor. Often I tell them to put a piece of wood between the camera and the wall and that will fix the interference caused by video ground loops.
Lastly there are video ground loop isolators (or “isolation transformers”). They are small pieces that are run in the line between the camera and DVR. Most of the time adding this piece will solve any ground loop interference in the video feed. I sold some to Joe and they worked great!
2MCCTV sells ground loop isolators for only $8.