The advantages of the shielded wiring system are mainly reflected in its strong ability to resist external electromagnetic interference and radio frequency interference; at the same time, it can also prevent the energy radiation of internal transmission signals to the outside world, and has good system security. For a shielded wiring system, in order to reflect its characteristics, we need to pay attention to the following two points when designing and constructing:
1. The function of the shielded wiring system requires that all connection hardware use shielded products, including: transmission cables, patch panels, modules and jumpers.
2. The installation of the shielded wiring system must be correct and well grounded. If the shielding layer of each connecting element of the transmission channel is discontinuous or poorly grounded, the transmission performance may be worse than that provided by the unshielded system.
Shielded wiring system
Part 1 Shielded Cabling System Installation
The installation of a shielded cabling system mainly involves two aspects: shielded cable termination and system grounding in floor wiring closets and work areas.
In view of the particularity of the shielding system, it is necessary to ensure that the shielding layer of the cable has good contact with the shielding layer of the module and the distribution frame in the range of 360 degrees, rather than connecting at some points, and the shielding layer cannot be in the same line. There is a break in the middle of the link.
Step 1: Use a special termination tool to remove the sheath of the shielded cable;
Step 2: Separate the stripped 4 pairs of twisted-pair core wires, do not disassemble each core wire pair, according to the core wire color line sequence indicated on the information module, flatly pull a short section of the corresponding core wire with both hands, Put the wires into the corresponding wire grooves one by one with a little force;
Step 3: After all the core wires are embedded, you can use the wire cutter to press the core wires into the wire groove one by one. Align the knife edge of the wire-punching tool with the wire grooves and wires on the information module, and cut off the excess wire outside the module. Repeat this operation, but also connect the drain wire in the cable to the metal sheet behind the module;
Step 4: Insert the plastic dustproof sheet of the information module into the twisted pair along the gap, and fix it on the information module, then cover the iron cover of the module, and press it tightly to complete the whole process of module production. Then put the prepared information module into the information socket;
Step 5: After the information module is made, of course, you can also test whether the connection is good. At this time, you can use a multimeter to measure. Set the gear of the multimeter to the resistance gear of x10, contact one needle of the multimeter with the corresponding core wire at the other end of the network cable, and contact the other multimeter pen to the edge of the card slot on the information module that is inserted into the core wire of the corresponding color (note that Not touching the core wire), if the resistance value is small, it proves that the information module is well connected, otherwise, press the corresponding core wire with a wire cutter until it is unobstructed. You can also use a professional tester, such as FLUKE, to select different shielding test standards according to different objects.
The installation of a complete shielded wiring system requires shielding everywhere and a continuous and complete shielding path in order to achieve the effect expected by the user. If you choose to use a shielded system, in addition to cables, the modules, distribution frames and other connectors need to be shielded, and supplemented by metal bridges and pipes. The principle of electrostatic shielding is to make the interference current flow into the ground through the outer shielding layer, so it is very important to properly ground the shielding layer.
Part II Grounding
Proper grounding of the shield is very important, otherwise it will not reduce the interference, but will increase the interference. Because when the grounding point is arranged incorrectly, the grounding resistance is too large, and the grounding potential is unbalanced, grounding noise will be caused, that is, a potential difference will be generated at two points of the transmission channel, so that interference current will be generated on the metal shielding layer. At this time, the shielding layer It itself forms one of the largest sources of interference, resulting in far less performance than unshielded transmission channels. Therefore, in order to ensure the screen effect, the shielding layer must be properly and reliably grounded.
The grounding accessories in the shielded distribution frame are grounding bus bars, which can connect all the shielding modules to a unified grounding body through it to form a grounding channel in the distribution frame.
There are two main types of grounding accessories for shielded distribution frames:
1. Grounding accessories installed in the patch panel
The grounding accessories installed in the distribution frame are flexible. When the shielded wiring system installation module is inserted into the distribution frame, its metal shell automatically forms a good connection with the grounding accessories, completing the grounding of the shielding module.
2. Independent grounding accessories
Independent grounding accessories can be converted into shielded distribution frames from special unshielded distribution frames. Such shielded modules generally contain grounding interfaces for pluggable wiring. After the shielding module is inserted into the distribution frame, insert the bonding wire in the grounding fitting to the grounding interface of the shielding module to form the grounding connection of the shielding module.
The patch panel should be equipped with grounding stakes so that the grounding conductor from the cabinet can be connected to it. The traditional method used for shielded patch panels is to ground through metal posts in the cabinet, which is no longer used.
The shielding grounding of the patch panel can be done in the following ways:
1. Each shielded distribution frame is connected to the bus bar of the cabinet through its own grounding wire to form a star-shaped grounding structure;
2. Install the grounding copper bar at the bottom of the cabinet, and use an independent grounding wire to connect the grounding copper bar to the grounding stake (grounding copper bar) in the wiring room (telecom room), so that the grounding between each cabinet forms a star-shaped grounding structure ;
3. The cross-sectional area of the grounding wire should be greater than 6mm2;
4. Both ends of the grounding wire should use cold-rolled solder tabs commonly used by electricians to prevent the wires from spreading and forming a short circuit;
5. In order to improve the discharge capability of high-frequency interference signals, it is recommended that the grounding wire needs to be braided to meet the skin effect requirements of high-frequency current with a larger surface area.
In the installation project of shielded wiring system, in addition to the need for high-quality wires and connectors, good construction skills and meticulous work attitude are essential. Pay attention to the details in the construction process, and do a good job in each grounding link in the shielding system. I believe that high-quality shielding projects will be made.
