Grounding symbols include general grounding, protective grounding, anti-interference grounding, chassis ground, equipotential body, etc., the standard cartographic symbols, please refer to the following figure:?
Grounding letters and symbols mean:
PE, PGND, FG-protective ground or chassis;
BGND or DC-RETURN-DC-48V (+24V) power supply (battery) return;
GND-work ground;
DGND-Digital ground;
AGND-Analog ground;
LGND-Lightning protection ground.
1, the general grounding symbol is a vertical and three horizontal, vertical and the first horizontal connection.
2, no noise grounding symbol is the general grounding plus half of the round mouth facing down.
3, protective grounding symbol is the general grounding plus a circle wrapped around the lower three horizontal.
Electrical grounding arrow symbol legend, in the lightning protection and grounding plan, the expression of the meaning of the lead with an arrow legend is shown in the following figure:
Grounding technology:Grounding is the establishment of a low-resistance pathway between the system and a potential reference, the same grounding point of the connecting line between the known as ground wire.
There are two general meanings of "ground" for electronic equipment: one is "earth". Earth as the zero potential, the metal casing of electronic equipment, circuit reference point connected to the earth, there is the role of protecting equipment and personnel safety, such as protective grounding, lightning grounding, etc., usually called "safety ground".
The other is the "system reference ground". In the weak power system grounding does not necessarily mean that the real sense of the earth connected to the ground, improve system stability, shielding and protection to enhance the role of electromagnetic compatibility of the system, when necessary, can also be done to connect the "earth" processing, usually referred to as "signal ground".
Grounding symbols: PE, PGND, FG - protective ground or chassis; BGND or DC-RETURN - DC - 48V (+24V) power (battery) backflow; GND - working ground; DGND -digital ground; AGND-analog ground; LGND-lightning protection ground.
The common types of grounding are as follows:
Repeated grounding, protective grounding, work grounding, lightning protection grounding, shielding grounding, anti-static grounding and so on.
Repeated grounding
Repeated grounding is in the neutral point directly grounded system, in the zero trunk of one or more places with a metal wire connected to the grounding device.
In the low-voltage three-phase four-wire neutral point directly grounded line, the construction unit in the installation, the distribution line should be the zero trunk and branch line terminal grounding, zero trunk every 1 kilometer to do a grounding.
For more than 50 meters from the grounding point of the distribution line, access to the user at the zero line should be repeated grounding, repeated grounding resistance should not be greater than 10 ohms.
Protective grounding
Electrical equipment under normal circumstances is not electrically charged metal casing and metal support and the earth for electrical connection, known as protective grounding. Protective grounding is mainly used in the neutral point is not grounded in the power supply system.
If the protective grounding measures are not used, then the human body touches the charged shell, due to the transmission line and the earth between the presence of distributed capacitance and constitute a circuit, so that the human body has a current through the electric shock accident.
If the electrical equipment using protective grounding measures, then the human body touches the charged shell, the human body and the protective grounding device resistance in parallel. Because the grounding resistance is less than the human body resistance, the current through the human body can be considered very small, the current almost does not pass through the human body, to avoid electrocution accidents.
Working ground
Earth network schematic ground is in order to make the system as well as the instrumentation connected to the system can operate reliably and to ensure the measurement and control accuracy of the grounding. It is divided into machine logic ground, signal circuit ground, shielding ground, in the petrochemical and other explosion-proof systems and intrinsically safe ground.
Lightning protection ground
Lightning protection ground is composed of part of the lightning protection measures, its role is to introduce the lightning current into the earth.
The lightning protection of buildings and electrical equipment is mainly with lightning arrester (including lightning rods, lightning straps, lightning nets and lightning protection devices, etc.).
The lightning arrester is connected to the protected equipment at one end, and the other end is connected to the grounding device. When a direct lightning strike occurs, the lightning arrester will lead the lightning to itself, and the lightning current will enter the earth through its lead wire and grounding device.
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 to the building's metal equipment, metal piping and reinforced steel structures, etc.; lightning waves will be along the low-voltage overhead lines, TV antennas invade the house, causing 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 line and into the house before the insulated porcelain vase iron foot grounding.
Shielded ground
It is an effective measure to eliminate the hazards of electromagnetic fields on the human body, but also an effective measure to prevent electromagnetic interference. High-frequency technology has been widely used in electric heating, medical care, radio broadcasting, communications, television and navigation, radar and other aspects. The human body under the action of electromagnetic fields, absorbed radiation energy will occur biological role, causing harm to the human body, such as slight trembling fingers, skin scratches, vision loss. Generate magnetic field of the equipment shell shielding device, and the shielding body grounding, not only can reduce the shielding body outside the electromagnetic field strength, to reduce or eliminate the harm of electromagnetic fields on the human body, but also to protect the shielding grounding body of the equipment from the outside world from the impact of electromagnetic field interference.
Anti-static grounding
To prevent the effects of electrostatic hazards and discharge, is the most important part of electrostatic protection.