How to test for a Ground Loop

Last updated
Save as PDF

A ground loop is any circuit where more than one ground connection exits between electrical devices. Ground loops in CCTV equipment can cause numerous problems, including wavy lines and overall poor video quality.

Ground loops occur, for example, when cameras and recorders are connected to different circuit breakers. A camera connected to a grounded wall transformer 100 meters from the recorder will more than likely be grounded to a different circuit breaker than the recorder. This makes it possible that there might be a few volts difference between the two power sources.

To test for a ground loop:

Set your volt meter to the most sensitive setting.
Disconnect the camera you want to test.
Place one contact on the case. (Try to use a screw on the case to ensure grounding)
Place the other contact on the outside of the connector.

Any value above 0 indicates a ground loop. Any value above 0.1V is outside of tolerance allowed for proper recording.
TARGET VOLTAGE: >=.09VAC<

Note: Be sure to check both AC and DC voltage for ground loops.

The fix to this type of problem is to first confirm that no device is electrically grounded to a separate building or structure.

Relocate cabling away from all light ballast and all other power cables. This should be a standard installation practice.
Run a ground cable from each camera/device back to a common ground strap.
All devices must be grounded to the same cable/ground strap.
Consult with an electrician regarding local building codes in your region. Electrical code varies from state to state and even from county to county in some areas.

Note: Never remove any safety earth ground connectors. 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.

Insulate all video interconnections. Be sure all coaxial connectors are wrapped with electrical tape to prevent them from coming in contact with grounded conduit or another source of energy.