How do I identify/measure a ground loop?

Issue

Getting noise/lines in my video.

Product Line

Pelco Video Management

Environment

  • Analog cameras
  • DVR
    • DX8100
    • DX4500 / DX4600
    • DX4700/DX4800 Series
    • DSSRV + ENC5416 or ENC5516
    • DSSRV2 + ENC5416 or ENC5516
    • DS Xpress
    • DS ReavlVue
    • DS1000
    • DS Enterprise
    • DVXi with Master Control
  • IP Video Encoder
    • NET4500 series (NET5401, NET5402, NET5404)
    • NET5500 series (NET5501, NET5502, NET5504, NET5508, NET5516)
    • PelcoNet series (NET101, NET104, NET300, NET350, NET4001)
  • Matrix
  • Multiplexer

Cause

A ground loop is any circuit where more than one ground connection exists 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.

Resolution

To test for ground loop:

  1. Set your volt meter to the most sensitive AC setting.
  2. Disconnect the camera you want to test.
  3. Place one contact on any exposed metal of the chassis
    • Bare metal screw
    • Outer ring of the BNC camera input
    • Grounding lug of the chassis
    • Shield or mounting screw of any "DB" style data/video ports (eg. DB9 serial port)
    • Probing a painted screw or other part of the chassis will result in a poor elctrical connection and affect your test results
  4. Place the other contact on the outside of the connector on the coax from the camera.
  5. Any value above 0 indicates a ground loop. Any value above .2V is outside the allowable tolerance.
  6. A ground isolation transformer can be used to filter out this voltage. Pelco part number GIT100. This will only filter out 60HZ noise.