Introduction to the four points of the earth's loop

[ Pacific Security Network News ]

Two points introduced the importance of the Earth Loop:

1. The potentials at different points on the ground are not equal. In short, this is the relationship between the power balance with the grid system, the grounding point method and position, the relationship between the neutral line and the ground line (open or short circuit), and high-power electrical equipment. Operating conditions, power-on and grounding methods, cable length and type are all related. Since the wires have resistance, the ground potentials are equal, and the potential fluctuations and unequalities are absolute. When an unbalanced fault occurs in the three-phase power grid, the ground potential changes drastically, and the local ground potential can be instantaneously increased by several tens to several hundreds of volts until the fault is eliminated. For engineering applications, we only need to know that “the ground potential at different points is different and fluctuating”, which is an objective reality.
2. The outdoor camera A is installed on a metal column outdoors. The monitoring room host system equipment case is connected to the ground safely. The video cable connects the camera to the host computer with BNC. At this time, the camera-video line is formed. The electrical connection loop of the host-ground-camera" is the concept of the ground loop. If the ground potential of point A has a potential difference of 10VAC with respect to the earth of the host point, this voltage is added to the shielding layer of the video cable, so that it is equivalent to the video signal ground between the camera and the host. An "interference voltage signal source and a ground resistance" is generated. This voltage can form a loop through the matching resistors at both ends of the video transmission circuit to generate an "interference signal" on the 75 ohm load. This is the common "ground loop." interference".

3, a monitoring system If there are multiple cameras installed on metal columns, metal towers, these cameras are connected to the earth, the system will form many complex "ground loops." If the security engineering firm is connected to the earth in an "unintentional manner", then the "second-class view" of the lightning protection manufacturer cited above - the front-end "equal potential connection" is a kind of artificially manufactured "ground loop". typical example.
4, cameras, transmission equipment, data communication equipment, etc., which already have lightning protection electromagnetic induction function, there is no need to add a lightning protection device. Equipment without lightning protection electromagnetic induction function can be solved by qualified lightning protection device. It is worth noting that the equipment with its own lightning-proof electromagnetic induction function is more effective than the general-purpose lightning protection device if it can be closely combined with the actual circuit design. We will not discuss it further here. The conclusion of this article "Talking about the grounding of the monitoring system from lightning protection grounding" is very simple. This is the principle of "single point grounding" of the security system.

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