How to judge the quality of network cables?
Jul 14, 2023
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In low-voltage engineering projects, network cables are widely used, and many friends often ask how to determine the quality of network cables. We all know that many common issues in projects are directly related to the quality of the network cables. Especially in surveillance projects, the most easily overlooked cause of failures is often related to network cables. As the most commonly used transmission medium, it is necessary for us to understand how to identify the quality of network cables. In this issue, let's summarize the four methods to determine the quality of network cables together.
In fact, there are generally two types of inferior network cables:
One type is the material of the core wire, such as copper-clad iron, copper-clad steel, and impure copper.
The other type is the wire diameter, which is often smaller than the industry standard.
1. Distinguish from the flexibility of the network cable.
Good ethernet cables are usually made of pure copper and have a soft and full feel. They can be easily bent and will gradually return to their original shape after bending. On the other hand, some manufacturers add other metallic elements to reduce costs, resulting in stiff wires that are not easily bent, have a depressed feeling, and do not recover their original shape after bending, which can easily cause wire breakage during use.
2. Distinguish from the flammability of the network cable.
Generally, the materials used to make ethernet cables must have flame resistance. When choosing an ethernet cable, you can check the flammability of the outer sheath to determine its authenticity.
In a specific test, you can cut about 2 centimeters of the outer sheath of the ethernet cable with scissors and then use a lighter to burn it. The outer sheath of a genuine ethernet cable will gradually melt and deform under the flame but will not ignite by itself.
You can also obtain a genuine ethernet cable and a counterfeit one, and simultaneously ignite them with a lighter. After a few seconds, the genuine ethernet cable should only emit white smoke and gradually melt and deform over time. On the other hand, the counterfeit network cable will easily catch fire in less than 2 seconds, accompanied by a significant amount of black smoke.
3. Distinguishing from the purity of the wire core color
Cut open the outer sheath, remove the insulation, and cut a small section of the conductor to observe the cross-section. If it is pure copper, it will appear uniformly golden. However, if there are iron, aluminum, or other alloys mixed in, obvious white or black impurities can be seen.
In addition, when heating the surface of the copper conductor with a flame, it will turn black on the outside but remain yellow on the inside. After wiping off the blackened part, the copper will still maintain its original color. However, if it contains iron, no matter how you wipe it, it will remain a dull black color.
To determine if the wire is heavily mixed with iron, you can cut a small section of the copper core, remove the surrounding plastic, and see if you can lift it with a screwdriver. Since screwdrivers have magnetic properties, they cannot be attracted to pure copper. However, with iron impurities, the situation is different. Counterfeit products with iron impurities can reduce costs but cause mismatched cable resistance, resulting in shortened transmission distances and decreased transmission speeds.
4. Using the resistance measurement method to determine the wire
4.1 This is the most direct and convincing method.
We use the resistance range of a digital multimeter to measure the corresponding cores of the network cable. The obtained resistance value can be compared based on the parameters provided below to determine the quality of the network cable.
4.2 How to measure?
When measuring the network cable, you can wrap a single-core copper wire around the multimeter, release your hand, and the measured resistance should be normal. Generally, different materials will have different resistance values. Note that when testing the resistance of a single core of the network cable, it must be the same core, meaning it should have the same color.
Take a 300-meter network cable as an example:
The standard resistance value for a single core of oxygen-free copper in Cat5e is around 28 ohms.
The standard resistance value for a single core of oxygen-free copper in Cat6 is around 21-23 ohms.
The standard resistance value for a single core of copper-clad aluminum in Cat5e is around 85 ohms.
The standard resistance value for a single core of iron in Cat5e is around 170 ohms.
The standard resistance value for a silver-plated network cable is around 45 ohms. (Here, "silver" refers to imported high-purity aluminum.)
For cables of the same length and diameter: The resistance of iron is approximately 7 times that of copper, and aluminum is approximately 1.7 times that of copper.
4.3 So, what is the standard for wire resistance?
The standard is that the resistance should be less than or equal to 9.5 ohms per hundred meters.
If the test resistance value of a full box (300 meters) of Cat5e or Cate6 cable exceeds 30 ohms, it is definitely not copper or the wire diameter is insufficient.
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