Detection of equipotential bonding effect of the h

2022-08-14
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Detection of equipotential bonding effect of shielding system

equipotential bonding conductors of shielding wiring system include: shielding layer of wiring subsystem, cabinet, bridge, metal pipeline, metal shell of network equipment, metal shell of terminal equipment and power protection ground wire in work area. This section discusses the relevant links of equipotential bonding involved in wiring engineering: impedance increases, cable starting point, open circuit and short circuit occur

1. A correct understanding of the grounding concept in the wiring system

a correct understanding of the "grounding" concept of the wiring system is the basis of engineering construction and testing. The narrow sense of "grounding" is mostly reflected in the lightning protection system, which regards the earth as a zero potential reference plane, and grounding is to introduce lightning signals into the earth itself, also known as "grounding"; The generalized "grounding" is mainly reflected in realizing electrical functions and improving the electromagnetic compatibility of the system. It takes the medium potential bonding conductor of the system as the zero potential reference plane, and the grounding is to include the electrical zero potential reference point, protective conductor, shielding layer, etc. into the equipotential bonding

if the purpose of "grounding" in shielded wiring engineering is to improve electromagnetic compatibility, it should be understood as bringing the shielding layer into the equipotential bonding system; If lightning protection is involved, it should be understood as connecting to the earth itself. For a typical example, the electrical equipment and wiring system inside the flying spacecraft cannot be connected to the earth, but they all have good electromagnetic compatibility because of the reliable equipotential bonding inside

the "grounding" detection in the shielded wiring project should focus on the "equipotential bonding" effect of each link of the system

2. Equipotential bonding effect of testing cabinet, bridge and metal pipeline

reliable grounding (equipotential bonding) is required for, bridge and metal pipeline in shielded and unshielded wiring systems. The equipotential connection can be obtained conveniently and accurately by using the clamp type grounding resistance meter to be sleeved on the grounding conductor of these equipment. In general shielded wiring engineering, if the reading is greater than

1 ω When, it is considered abnormal; For wiring in medical places, the reading should not exceed

0.2 ω (according to Article 12.7 and 12.8 of JGJ)

3. Check the distribution mode of AC power supply in the work area

the power protection ground wire in the work area is the only grounding path in the work area. During the wiring construction, the shielding layer of the information socket in the work area is not specially grounded. When using the network, the information socket is connected with the through the shielding jumper. The shielding layer of the wiring system is connected to the protective ground wire of the distribution system through the terminal of the equipment power line

to realize equipotential bonding

although the AC power supply does not belong to the scope of generic cabling design and construction, in order to ensure the cable shielding layer and equipment grounding in the work area, it is specially pointed out in 6.1.2

code for design of systems engineering

GB that the AC power supply in the work area should adopt the

TN-S

mode, that is, the power distribution mode in which the protective ground wire (PE

line) and the neutral wire (n

line) are separated

in the project acceptance, it is recommended to use special instruments to detect the relevant power sockets. For example, using the AC circuit analysis as shown in the figure

to test the socket that supplies power to the terminal equipment can not only inform the socket power distribution mode according to the requirements of the mandatory clause (22.1.2) in the code for acceptance of construction quality of building electrical engineering

gb, find the power hidden dangers that threaten the safety of people and equipment in the early stage, but also get the impedance value of the protective ground wire (pe

wire), providing quantitative data for troubleshooting and defining the grounding fault

4. Check the equipotential bonding effect of the cable shielding layer

as shown in the figure

, the shielding layer of the "permanent link" part of the wiring system is grounded at both ends respectively: one side of the distribution frame is grounded through the cabinet; One side of the working area is grounded through the power protection ground wire of the terminal equipment. On the premise of ensuring the qualified connectivity of the shielding layer itself, its grounding effect is completely determined by the grounding links on both sides

(1) measure the potential difference

"if there are two different grounding bodies in the grounding system of the wiring system, the ground potential difference should not be greater than

1Vrms". Tia-568-c.0 5.3.5

stipulates that at the end of horizontal wiring in the working area, the effective value of AC voltage (RMS) between the cable shielding layer and the protective ground wire of the power socket supplying power to the equipment (i.e. yellow green

PE wire) shall not exceed

1.0V

after confirming that the connectivity of the cable shielding layer is qualified, the wiring of the power socket is correct (PE

the line cannot have an open circuit, high resistance points, or dangerous voltage!) Then, as shown in the figure

, the AC voltage between the shielding cover of the information socket in the work area and the protection of the power socket with the "effective value" measurement function is directly measured. The toughening agent of toughening PBT is often used as the acrylate copolymer ground wire with core-shell structure (pe

wire), and the reading should meet the standard provisions

(2) test loop resistance

although the voltage between the information socket shield and the power supply

line can reflect the equipotential bonding, which allows the use of low melting point alloys, 3D printable elastomers and resins for open experimental junctions, because the terminal equipment jumper and equipment power line do not appear in the test, in practical application, if the jumper shield or equipment power supply

line appears open circuit or high resistance, The cable shielding layer cannot be well grounded in the working area. Only by confirming that the protective conductor of the whole circuit is in a low resistance state, it means that the equipotential bonding of the shielding layer is reliable

as shown in the figure

, after correctly connecting the jumper of the terminal equipment with the power line, use the clamp type grounding resistance meter to connect it to the shielding jumper or the power line of the equipment to test the resistance of the whole circuit, and verify the actual effect of equipotential bonding of the cable shielding layer. The theoretical calculation (see the "appendix" for the calculation process) shows that under normal circumstances, this test value should be less than

4 when you are equipped with a high-quality experimental machine ω, And the smaller the better. This resistance value also meets the provisions of GB

7.0.4 to avoid the injury caused by the falling off of face bricks: "the generic cabling system should adopt the grounding system of common grounding. If the grounding body is set separately, the grounding resistance should not be greater than

4 ω。” Requirements

because the above test objects are shielding layer and protective conductor circuit, whether the equipment works or not does not affect the test results. If the value exceeds the standard, further search and eliminate the fault

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