Jumper selection in general wiring
Usually the jumpers used in the local area network LAN mainly come from three channels:
1. The matching jumper of the same brand as the overall link product;
2. On-site production of jumpers;
Third, buy jumpers in the computer market. In addition to the professional test of the manufacturer of the matching jumper, it is difficult for ordinary users to know the quality of the jumper produced on site or purchased in the market. Unqualified jumpers will seriously affect network transmission efficiency and network stability, and counterfeit and shoddy products will even cause irreversible damage to the connecting hardware (interfaces of computers or switches) associated with them, resulting in the entire system. paralysis.
Next, we compare the jumper conditions of these three channels from several aspects, and analyze the comparison results from the structure, manufacturing process and materials of various jumpers.
Project Brand Finished Jumper On-site Production Jumper Market Purchase Jumper
Transmission performance (electrical performance) is good and poor, individual differences are large
Reliability (Internet connection) Good Poor Unknown
The price is unknown
Adaptability (with network card, connection hardware) is good and poor, individual differences are large
Flexibility (distance length) good poor
Unknown service life
Ease of use unknown
Integrated wiring jumper
1. Jumper comparison
The jumper structure is mainly composed of three aspects: the jumper cable conductor, the crystal head, and the protective sleeve. Let us first take a more intuitive look at the physical comparison of the finished jumper and the field-made jumper.
1. Brand finished jumper
The integrated wiring standard requires that the cable conductor of the finished jumper is AWG26 (7/0.16mm) or AWG24 (7/0.20mm) bare soft copper stranded wire. The cable of this structure is relatively soft and has good bendability, which ensures that the jumper is very convenient during use. At the same time, because it is a stranded copper wire, it is easier to manage the wire on site. Use FLUKE to select the jumper single test, the performance margin of RL and NEXT exceeds the TIA568B standard before leaving the factory.
Since the finished jumper belongs to the same brand as the network cable and connecting hardware, it is easier to keep the characteristic impedance of the entire channel consistent, so as to obtain the ideal RL value.
2. On-site production jumper
The cables used to make jumpers on site are generally leftover wires from horizontal wiring. The conductor structure of the horizontal cable is a solid core conductor. Cat5e uses AWG24 (1/0.511mm), and Cat6 uses AWG23 (1/0.574mm) bare soft copper single wire. The cable of this structure is relatively hard and has poor flexibility, and it is difficult to manage the cable on site. In addition, because the crystal head installed on site is crimped with a hand-pressing simple crimping tool, the crimping reliability of the crystal head gold piece and the solid core conductor has a great relationship with the operation of the crimping operator. The performance of the jumper produced on site , Using FLUKE to select the jumper single test, the performance of RL and NEXT is very different, and the reliability of the mechanical connection point is obviously worse than that of the brand product jumper.
3, the market to buy jumpers
Due to the variety of channels for patch cords purchased in the market, users who are not very professional about patch cord products may even buy patch cords made on site. Even if you buy a brand jumper, it may be a "copycat" product. The author once found at a project site that the jumper cable used by the customer for testing is a 5/0.16mm stranded aluminum wire, and the jumper is identified as a product of a well-known brand. Using FLUKE to select a single jumper test, the performance margin of RL and NEXT are almost all less than -10.0dB, which is obviously a fake and shoddy product, and it is also a problem that is easy to encounter when buying in the general market.
2. Analysis of jumper raw materials
To meet the jumper performance specified by the TIA/EIA568B.2 standard, high-quality raw materials must be used. The raw materials involved in the jumper include two parts: the jumper cable and the crystal head:
1. Jumper cable
The conductor is made of oxygen-free round copper rod, the resistivity is <0.017241; the insulation is made of HDPE, and the better brands such as UCC3364;
Generally, the matching jumper and the field-made jumper can meet the requirements in terms of materials, but the jumper purchased in the market is difficult to guarantee. The material cost of some inferior jumpers on the market is very low, and the performance can only ensure conduction. Mainly reflected as:
Conductor: The jumper purchased in the market may be made of aluminum, or it may be made of inferior copper. Such conductors have high resistivity and poor ductility;
Insulation: better ones may use general HDPE insulating materials, and poor ones may use recycled materials, which have large dielectric constant and unstable, and low elongation. In addition to having little electrical performance, this type of jumper also suffers from short lifespan and poor reliability.
2. Crystal head
The metal sheet substrate of the RJ45 connector (crystal head) is mainly made of phosphor bronze nickel-plated and then gold-plated. Generally, the thickness of the gold-plated layer is 30u”, 50u”, and the thickness of the gold-plated layer of the six-type crystal head is generally 50u” (1.27μm). The performance does not deteriorate when the head is plugged and unplugged more than 750 times; the plastic shell is PC, which conforms to UL-94-V0, and the crystal head shrapnel is required to be plugged and unplugged more than 750 times without breaking.
The metal sheet, gold-plated layer and plastic shell material of the matching brand finished jumper crystal head are all tested in the factory according to the standard, which can ensure the mechanical and electrical performance requirements of the product. If the crystal head used in the on-site production of jumpers comes from the original product, the quality can be guaranteed. If the crystal head is purchased in the market, the mechanical, electrical and fire performance of the material is difficult to guarantee.
Let's compare two crystal heads: sample A is a product provided by a supporting manufacturer, and sample B is a product of an international well-known brand purchased in the market. The color of the metal sheet of sample A (left) is dull and close to gold; the color of the metal sheet of sample B (right) is brighter, similar to brass (there are obvious spots on the surface of the metal sheet); the plastic shell of sample A is transparent and uniform, and the sample B is transparent and white with fine cracks.
Let's compare a set of test values for the coatings of these two products:
Project Sample A Sample B
Through the comparison of the above data, it is found that the thickness of the gold-plated layer of sample A is about 50 μ” (1.25 μm), while the thickness of the gold-plated layer of sample B is only about 3 μ” (0.081 μm), which is called flash plating in the industry. The thickness of the gold-plated layer affects the crystal The cost of the head is about 30%-40%.
3. Analysis of jumper manufacturing process
Before introducing the jumper production process, let's understand 2 parameters related to the jumper:
In the production process of the matching jumper, the crystal head is automatically crimped by machine equipment, and the tail sleeve is injection-molded at one time. The automatic crimping of the equipment ensures that after the metal sheet of the crystal head is crimped, the embedded depth meets the requirements of the FCC specification. The injection molded boot can increase the reliability of the crimping part of the jumper, improve the stability of the adaptability, and obtain a longer life.
The jumpers made on site generally use simple crimping tools and do not use any boots for protection. This crimping method is difficult to ensure that the embedded depth of the sheet meets the requirements, and it is impossible to ensure a good and uniform mechanical pressing force. In addition, because there is no tail sleeve protection, it is easy for the jumper to remove the copper cable from the crystal during use. The jumper is pulled out from the inside of the head, and the circuit is broken due to poor contact. The stability and life of this jumper are relatively poor.
The production process of jumpers purchased in the market is different. The sequins may be mechanically crimped or other methods, and the tail sleeves are generally also formed by one-time injection molding. The service life of the jumper purchased in the market is not determined by the reliability of the crimping part, but mainly by the material of the product.
Fourth, some suggestions for purchasing jumpers
After the project is over, IT personnel sometimes have to purchase jumpers or crystal heads when maintaining the computer room. Here are some suggestions for your reference!
buy crystal heads
Look at the appearance: the metal sheet of the crystal head is bright and free of oxidation spots; the partitions are even and free of burrs; the crystal head is transparent and free of impurities and cracks.
Folding the shrapnel: Bend the shrapnel of the crystal head 2~3 times to 180°, and it will not break or turn white after rebounding (if conditions permit, a crystal head can be crimped on site for plugging and unplugging with the module for 5~10 times).
Shop Finished Jumpers
The purchase of finished jumpers requires the same process as the purchase of crystal heads, but also requires a simple verification of the jumper cable and process. Based on experience, it is summarized into the following 3 steps:
Look at the end face of the jumper crystal head: if the cable conductor is silvery white, the conductor is aluminum or even iron wire (inferior product); if the end face cable conductor is golden yellow, the conductor is copper (may be a qualified product) ).
Look at the cable itself: some cables have a very smooth surface without any lines. It may be that the pitch of the cable is very large and the outer diameter of the insulation is relatively small. This kind of product has poor performance (may be inferior product); Regular thread shape, this kind of pattern is caused by the small pitch of the cable pair twist and the tight outer sheath of the cable (may be a qualified product).
Feel the tightness of the cable: some cables feel very loose, and you can't even feel the insulating core wire inside the outer cover. Bend the cable nearly 180°, and the outer cover is almost flat (basically inferior products); some The cable feels very close to the touch, and the twist distance of the pair can be clearly seen when bent nearly 90°, and the outer protection is basically kept round (basically a qualified product).
Comprehensive analysis, when buying finished jumpers, in order to buy qualified products, it can be judged from the following aspects:
1. Observe the end face of the crystal head, the conductor is golden yellow (copper conductor); the surface of the crystal head is smooth without burrs, the size of the partition is uniform, and the overall appearance is transparent and without cracks
2. Regular lines can be seen on the surface of the cable (the twisting pitch of the cable is small), the cable is tightly squeezed by hand, and the twisting distance of the cable can be clearly seen when it is bent at about 90° and remains basically round .
3. The crystal head shrapnel is bent 2 to 3 times at 180°, and the bending place will not crack or turn white.
4.Unfold the packaged jumper wire, and then rewind the jumper wire in the original direction. It can be flat on the table without tying the cable tie.