Ground loops are an unwanted phenomenon caused by the ground potential difference between two distant points.
It is usually the difference between the camera and the monitor ground point, but it could also be between a camera and a switcher, or two cameras, especially if they are daisy-chained for synchronization purposes.
The picture appears wavy and distorted. In many cases, it can be identified as a “hum bar” or dark horizontal bar in the picture. Small ground loops may not be noticeable at all, but substantial ones are very disturbing for the viewers.
In other words, the ground loop is a type of interference that generates horizontal bars rolling on the screen of a CCTV system as shown in the picture below. Here in this article we will explain and offer tips on how to eliminate the ground loop issue in CCTV systems.
Usually, ground loops are an after-the-fact type of problem in which the end-user blames the installer, the installer blames the manufacturer, and actually, nobody is at fault. Neither the manufacturer nor the installer can predict where a loop will occur.
Only after the system is installed can it be determined if a problem will exist. Ground loop problems can be corrected. It is important for both the dealer and the end user to be aware that this problem can occur.
A ground loop problem may occur at several points in the system, and each occurrence of the problem must be corrected individually.
Loops can occur between a camera and monitor, from a camera to a switcher, or one of many other possibilities. Not all ground loops show up as picture disturbances. Erratic or strange behavior of other devices can be traced to grounding problems.
How to eliminate the CCTV ground loop?
1. Ground all devices to a single point
The best method to avoid ground loops lines is to ground all the devices to a single point, so there will be no voltage difference between these elements.
An example is shown below. Note that all the devices are grounded and there will be no interference. If this method is too complicated, go to the next steps for easier solutions.
2. Electrical cable distance
One of the reasons why you’re experiencing the ground loop effect is that you’re running your security camera’s cable over a high power source.
This can also be caused by load unbalance when the 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/30cm) if possible especially not directly on top of them.
In some cases when this is not possible, try using high quality coaxial cables with as much shield as possible to help avoid interference that may be caused by electrical cables.
3. Camera insulation
Another issue that creates ground loops are metal structures. In many cases, the installers mount the CCTV cameras to the side of a metal building (or on a metal pole) and the entire building is one large conductor.
One way to solve this problem is to place a piece of insulation (such as wood or plastic) between the camera and the wall and that will fix the interference caused by video ground loops.
4. Invert the plug
If you are using a 24VAC power supply (transformer) and you have this problem you can reverse the wire on the power supply and the interference will go away.
This is an old trick that some of the old-school CCTV installers use. Note that this method works only for the 24VAC power supply and it won’t work for the 12VDC.
5. CCTV ground loop isolator
The easiest and most cost-effective way to remedy a ground loop problem is to use a ground loop isolator transformer.
This device connects anywhere between the head end and camera on the video cable and isolates the video ground.
The ground loop isolator transformer is relatively inexpensive and simply connects via BNC connectors between the camera and end device. So, if the ground loop is giving you headaches, purchase a ground loop isolator and get over it.
6. Never remove any safety earth ground connectors
Inexperienced installers may sometimes claim the way to fix this problem is to remove the “3rd Prong” on electrical supply cords.
This should NEVER be practiced due to the safety hazards and will void all UL certifications. Additionally, this will cause the chassis to become electrically energized and become a safety hazard.