How to judge the quality of lan cable? As we all know, some small failures often occur in the project, in fact, a large part of the reasons are directly related to the lan cable.
Especially in the monitoring project, the most easily overlooked fault is the lan cable. As the most commonly used transmission carrier, it is necessary for us to understand how to identify its advantages and disadvantages.
In fact, there are no more than two kinds of poor quality lan cable:
One is the material of cable core, such as copper clad iron, copper clad steel, miscellaneous copper, etc.
The other is the size of cable diameter, which will be much smaller than the national standard.
1、 Judging from the flexibility of the cable
Because good cable is generally made of pure copper, and the net wire produced with pure copper should feel soft and full of hand, and can be bent arbitrarily, and will slowly recover its original shape after bending;
In order to reduce the cost, some manufacturers add other metal elements to the copper in order to reduce the cost. The cable made is relatively hard, not easy to bend, with concave feeling, and it is not easy to restore the original shape after bending, so it is easy to break the cable in use.
2、 Distinguishing from the flammability of the lan cable
Generally speaking, the material used to make up the lan cable must be flame resistant. Therefore, when selecting the cable, you can check the flammability of the outer skin of the cable to identify the authenticity.
In the specific test, we can cut the outer skin of the lan cable about 2cm with scissors, and then burn it against the outer skin with a lighter. The outer skin of the genuine lan cable will be melted and deformed gradually under the fireworks barbecue, but the outer skin will not burn itself;
We can find a section of genuine and fake lan cables, and ignite them with a lighter at the same time. After a few seconds, the authentic lan cable should only smoke white smoke and gradually melt and deform over time. However, the fake and inferior lan cable will be easily ignited in less than 2 seconds, and there will be a large amount of black smoke.
3、 Distinguish from the color purity of the lan cable’s cable core
Cut the outer layer of the sheath, pull out the insulation, cut a small section of the conductor to observe whether the cross-section copper color is uniform. If it is pure copper, it will be uniform gold color; but if iron or aluminum or other alloys are mixed inside, obvious white spots or black can be seen.
In addition, the surface of conductor copper will turn black with positive fire, while the inner color will remain unchanged yellow. After wiping off the blackened part, the copper will still keep its original color; but if there is iron, no matter how you rub it, it will be dull black.
To judge whether there is serious iron inclusion in the lan cable, you can cut a small section of copper core, remove the plastic wrapped, and see if it can be lifted with a screwdriver. Because the screwdriver head is magnetic, if it is pure copper, it can not be absorbed. After doping iron, it will reduce the cost, but it will cause cable resistance mismatch, which will shorten the transmission distance and reduce the transmission speed.
4、 The determination of resistance value method of the lan cable
This is the most direct and persuasive method.
We use the resistance of the digital multimeter to measure the corresponding core cable of the lan cable. The resistance value obtained can be compared according to the parameters given below, so as to know the quality of the lan cable.
How to measure it?
When measuring the lan cable, the single core copper wire can be wound on the universal meter and the hand can be released. The measured resistance is normal. Generally speaking, different materials have different resistance values. Note that the lan cable single core test resistance, must be if the same core test, that is, the same color.
Based on the length of 300m lan cable:
The single core standard resistance of super-5 oxygen free copper is about 28 ohm;
The standard single core resistance of six types of oxygen free copper is 21 ~ 23 ohm.
The single core standard resistance of super-5 copper clad aluminum is about 85 ohm;
The single core standard resistance of super-5 iron is 170 ohm;
About 45 ohm copper-clad silver wire; (here the so-called silver is a kind of imported high-purity aluminum);
The same length and same diameter cable: the resistance of iron is about 7 times of that of copper, and that of aluminum is about 1.7 times of that of copper.
So what is the standard of lan cable’s resistance?
The standard is 9.5 ohm or less in 100 meters.
If the test resistance value of a full box (300m) of super class 5 or super-6 cable exceeds 30 ohm, it must be non copper or insufficient cable diameter.