The metal casing or rack insulated from the electrically charged part of the electrical equipment with the ground to make a good grounding is called safety ground. If the chassis is not grounded, the chassis with a higher potential, the human body after contact with the risk of electric shock, when the insulation is broken, the ground short-circuit current will flow along the ground wire and the human body two paths into the earth at the same time. Usually used in computer rooms AC equipment chassis (such as: air conditioners, frequency and voltage regulators, transformers, UPS backup power supply and other equipment shell) should also be grounded according to the relevant electrical specifications.
Lightning grounding
Composed of a part of the lightning protection measures. Its role is to introduce the lightning current into the earth. Lightning protection of buildings and electrical equipment is mainly with lightning arrester (including lightning rods, lightning straps, lightning nets and lightning protection devices, etc.). One end of the lightning arrester is connected to the protected equipment, and the other end is connected to the grounding device. When the occurrence of direct lightning, lightning arrester will lead the lightning to itself, lightning current through its lead line and grounding device into the earth. In addition, due to lightning caused by electrostatic induction side effects, in order to prevent indirect damage, such as house fires or electrocution, etc., usually also need to be grounded inside the building of metal equipment, metal piping and reinforced structures; lightning waves will be invaded along the low-voltage overhead line, TV antennae into the house, caused by insulation breakdown of electrical equipment inside the house, resulting in fires or personal injury or death from electrocution, so it is also necessary to be on the line and into the house before the Insulated porcelain vase iron foot grounding.
Working ground
In order to make the system as well as the instrumentation connected to it can operate reliably and ensure the accuracy of measurement and control of the grounding. It is divided into machine logic ground, signal circuit ground, shielding ground, in the petrochemical and other explosion-proof systems, there are intrinsically safe ground
Joint grounding method
Joint grounding method is also known as the single-point grounding method, that is, all the grounding system **** with a **** the same "ground". Joint grounding has some of the following characteristics:
(1) the grounding system of the entire building consists of a cage-type equalizer, for direct lightning, the same floor of the building at various points is relatively uniform; for induced lightning, the cage-type equalizer and the building's frame structure of the electromagnetic field interference from the outside can provide a shielding effect of 10-40dB;
(2) the general Joint grounding method grounding resistance is very small, there is no coupling effect between the various grounding bodies, which is conducive to reducing interference;
(3) can save metal materials, occupies less land.
From the above, it is easy to see that the use of joint grounding can effectively suppress the interference of external high-voltage transmission lines.
Anti-static grounding of the ground wire should be connected in series with a 1 megohm current-limiting resistor, that is, through the current-limiting resistor connected to the grounding device. Grounding resistance is not the smaller the better? Why string resistance?
Computer grounding is aimed at the easy flow of ground current, which requires as little grounding resistance as possible. The grounding of the computing center should minimize noise-induced potential shifts, and it should be noted that signal circuits and power circuits, high-level circuits and low-level circuits can not use the same **** ground loop. For network wiring with high transmission bandwidth requirements, isolated shielded grounding should be used to prevent interference from electrostatic induction. Strive for simplicity, economy and effectiveness in the design of the grounding if you can effectively combine with shielding, will be able to better solve the interference, noise suppression.
See Baidu encyclopedia "grounding"
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