Grounding and neutral connection of temporary elec

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Grounding and neutral connection of temporary electricity for construction

current and future electrical equipment of medical materials on the construction site, especially various electrical equipment whose metal shell is electrified (called leakage) due to aging insulation or mechanical damage and other factors, in this case, if someone touches it, it shows its non-Newtonian fluid characteristics; 5. Electric shock or electric shock accident will occur after 2 times of processing. This contact between the human body and the exposed conductive parts that become electrified under fault conditions is called indirect contact. In the construction site, due to the impact of the site environment and conditions, indirect electric shock is often more common than direct electric shock, and the harm is also greater. So. In addition to taking safety measures to prevent direct contact with electricity, safety technical measures to prevent indirect electric shock must also be taken

1. Grounding of electrical equipment

the so-called grounding is to electrically connect a conductive part of electrical equipment with the earth by using conductors, no matter how good the product quality is. Electrical connection refers to the connection between conductors with zero resistance; In fact, connecting two or more conductors with metal and other conductors can be called electrical connection. In short, the metallic connection between equipment and the earth is called grounding. There are four kinds of grounding: working grounding, protective grounding, repeated grounding and lightning protection grounding. It is briefly described as follows:

(1) working grounding. In the power system, the grounding required for operation (such as the grounding of the power center point in the three-phase power supply system) is called working grounding. In the case of working grounding, the earth is used as a conductor and can stabilize the voltage to the ground of the conductive part of the equipment

(2) protective grounding. In the power system, due to the need of leakage protection, the metal shell of electrical equipment that is not live under normal conditions and the metal components (frames) of mechanical equipment are grounded, which is called protective grounding

(3) repeated grounding. In the power system with neutral point directly grounded, in order to ensure the function and effect of grounding, in addition to the direct grounding at the central point, one or more places on the neutral line are grounded again, which is called repeated grounding

(4) lightning protection and grounding. The grounding of lightning protection devices (lightning rod, lightning arrester, lightning wire, etc.) is called lightning protection grounding. Lightning protection grounding is mainly used as lightning protection device to conduct lightning current to the earth

2. Zero connection

working zero connection. Working neutral connection means that the electrical equipment is connected to the working zero line due to operation needs. One pole of single electrical equipment (including lighting devices) with rated working voltage of 2201 at the construction site and selected V of Jinan experimental machine range is connected to the working zero line, which belongs to working zero connection. When the single-phase electrical equipment operates, its working neutral line has normal working current

protection is connected to neutral. Protective neutral connection refers to the connection between the conductor part of the electrical equipment that is not live under normal conditions and the protective zero line. The conductive part refers to the part that can conduct electricity but does not necessarily carry the working current. In the construction site of the special protective zero line of TNS system, the protective zero line shall be connected with the special protective zero line. The exposed conductive parts that are not electrified under normal conditions of the following electrical equipment shall be protected and connected to neutral:

(1) metal shells and bases of motors, transformers, electrical appliances, lighting fixtures, electric machinery and electric tools (for hand-held electric tools that generate vibration, the connection points of the protective zero line shall not be less than two)

(2) metal parts of transmission device of electrical equipment

(3) metal frame of distribution panel and control panel

(4) metal framework, box body of indoor and outdoor power distribution devices and metal fence and metal door close to live parts

(5) metal protective tubes for power lines, laying steel cables, crane rails, metal operating platforms for sliding formwork and large steel formwork

(6) metal shells and supports of switches, capacitors and other electrical devices on power line poles

exposed conductive parts refer to conductive parts that are easy to reach and parts that are not live but can become live under fault conditions

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