What Is a Shielded Cable?

Shielded cable is a transmission line that uses metal mesh braid to wrap signal lines. The braid is usually red copper or tinned copper. The wire and cable industry is the second largest industry in China after the automotive industry, with both product satisfaction and domestic market share exceeding 90%. In the world, China's total output value of wire and cable has surpassed the United States, becoming the world's largest wire and cable producer. With the rapid development of China's wire and cable industry, the number of new enterprises has continued to rise, and the overall technical level of the industry has been greatly improved.

GB12972.6 --- 91 ^[1]

Suitable for transformers and similar equipment ^[2]

1. Rated voltage U0 / U 3.6 / 6KV;

2. The long-term working temperature of the cable conductor is 90 ° C;

3. The minimum bending radius of the cable is 6 times the diameter of the cable;

4. The cable must not be exposed to sunlight for a long time;

5. The bottom core of the cable must be well grounded.

1. The finished cable should withstand the power frequency AC voltage experiment

Shielding is to ensure the transmission performance of the system in the presence of electromagnetic interference. The anti-interference performance here should include two aspects, namely the ability to resist external electromagnetic interference and the ability of the system itself to radiate electromagnetic interference. Theoretically, coating a layer of metallic shielding on the surface of cables and connectors can effectively filter out unnecessary electromagnetic waves (this is also the method used by most shielding systems). However, the effectiveness of this method How exactly? For a shielding system, it is not enough to have a metal shielding layer. What's more important is that the shielding layer must be well grounded, so that the interference current can be effectively introduced into the ground. However, in actual construction, the shielding system has some difficulties that cannot be ignored: due to the harsh grounding requirements of the shielding system, it is very easy to cause poor grounding, such as excessive ground resistance and uneven ground potential. There will be a potential difference between them, which in turn will generate a current on the metal shielding layer, causing the shielding layer to be discontinuous and destroying its integrity. At this time, the shielding layer itself has become a largest source of interference, which results in its performance being far worse than that of an unshielded system. Shielded wires need to be grounded at both ends when transmitting at high frequencies, which is more likely to cause a potential difference on the shielding layer. It can be seen that the requirements of the shielding system itself constitute the biggest obstacle to ensure its performance. A complete shielding system requires shielding everywhere. Once any point of shielding cannot meet the requirements, it will inevitably affect the overall transmission performance of the system. However, very few network hubs or computers in the market have shielding support, so it is difficult to achieve shielding of the entire transmission link ^[3]

Shield grounding is usually handled in two ways: single shield grounding and double shield grounding.

The single-ended grounding of the shield layer is to directly ground the metal shield layer at one end of the shielded cable, and the other end is not grounded or through protective grounding.

In the case where the shielding layer is grounded at a single end, there is an induced voltage between the non-grounded metal shielding layer and the ground. The induced voltage is proportional to the length of the cable, but the shielding layer does not circulate through the potential. Single-ended grounding is to eliminate the electromagnetic interference by suppressing the potential difference.

This grounding method is suitable for short-length lines, and the induced voltage corresponding to the cable length cannot exceed the safe voltage. The presence of static induced voltage will affect the stability of circuit signals, and antenna effects may sometimes be formed.

Double-terminal grounding is to connect both ends of the metal shield of the shielded cable to ground.

The continuous and rapid growth of China's economy has provided huge market space for cable products. The strong temptation of the Chinese market has made the world focus on the Chinese market. In the short decades of reform and opening up, China's cable manufacturing industry The huge production capacity formed has made the world look amazing. With the continuous expansion of China's electric power industry, data communications industry, urban rail transportation industry, automobile industry and shipbuilding industries, the demand for wire and cable will also grow rapidly, and the wire and cable industry has huge development potential in the future ^[2] .