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CCTV Groundloop Isolator

A common problem many installers face with CCTV installations is earth or ground loop problems. Many CCTV installers have seen the classic symptoms of the rolling humbar or the tearing picture but don’t understand the cause of the problem and the solutions to cure it. They may have even seen a small spark or felt a slight tingle when they disconnect interlinking cables from video recorders and other equipment; these are all signs of round loop problems.

So, what is a ground loop?

A ground loop occurs when there is more than one “ground” or “earth” between two pieces of equipment. Because the two pieces of equipment have multiple ground paths, loops (circuits) are formed in which current can flow. The current flowing through this unwanted circuit in the CCTV system can have a devastating effect on the system’s performance. The current flows through the shield of coaxial types of cable and instead of “dragging” any interference (usually 50Hz mains hum) down to a “true” ground at the receiving end of the cable, it actually picks this interference up (in its ground loop antenna!) and carries it to the sensitive inputs of CCTV equipment such as DVRs, Quads and Switchers.
The DVR, quad or switcher simply interprets this “interference hum” as part of the intended video signal entering the equipment and displays it on the monitor as a rolling “hum” bar.

By carefully using good CCTV power supplies you will minimize ground loops but if they still exist then a device that blocks the current flowing down the earth connection is an option. The HumBloc simply terminates ground loop currents in a cable and blocks the hum and interference carried in the ground loop.

How many Humblocs do I need to cure a problem?

The Humbloc should be fitted between the camera and the input of CCTV equipment such as a DVR that it is connected to; generally speaking, the Humbloc would be fitted at the rear of the DVR to its “video input(s)”. For example, in a 4 camera system, it is possible that only one camera has an earth loop problem and that one Humbloc may cure it. In reality, though if you experience groundloop problems in a CCTV system it is often best to fit one Humbloc to every input as earth loops may sometimes not be sufficiently strong to show up as humbars but they may still cause erratic operation of equipment due to the unwanted currents flowing through the earths. The motto here being better to be safe than sorry. The HUMBLOC helps prevents the “ground loop” in the cable blocking the “humbar” interference on the monitor.


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