Compared with air conditioners, televisions, automobiles, etc. Wire and cable are relatively different products. Take air conditioning as an example. At present, there are only a few large air-conditioning brands on the market, such as Gree, Oaks and Midea. When buying, it is easy to finalize what brand to buy through the feedback from friends and relatives around you. There are several or even a dozen well-known brands in almost every place of wires and cables. As long as you pay attention, you can find several brands with high frequency from bus body advertisements, billboards on the street and billboards on the expressway. Usually, these enterprises have good strength and relatively sound product-related qualifications, such as national compulsory CCC certification and wire and cable production licenses. The products of such enterprises are the first consideration when you buy wires and cables.
Second, the price of wire and cable
Take air conditioning as an example, the overwhelming media publicity will make you have a clear understanding of the performance of air conditioning, such as frequency conversion, mute and so on. If you decide to buy inverter air conditioners, just visit Gome, Suning and major supermarkets, the prices of all brands are basically well-thought-out. Different wires and cables, the same specifications and models, different manufacturers, different brands, the price gap is very large. We have done market research, taking PVC insulated wire (BV2.5 square meters) as an example, which is also a brand-name product. The diameter of copper wire is also 1.78 mm and the length is 100 m. Insulation 9400 yuan/ton PVC, the price (based on the Yangtze River nonferrous metal mesh copper futures quotation 60000 yuan/ton) from. At present, the price control of wire and cable in our country is still not perfect, because when we buy wire and cable, we must shop around and choose the right product among the products of the same quality.
Third, the cost calculation of wire and cable
If you want to buy high-quality and cheap wires and cables, you must first have a general understanding of the cost calculation of wires and cables.
The wires and cables we often use belong to cloth wires, also called household cables. The conductor structure is simple and the cost is easy to calculate. Wires consist of insulators (PVC) and conductors (copper or aluminum). Firstly, the cost calculation method of conductor (copper) is introduced:
1, calculate the weight of copper first.
Weight of copper = density of copper (0.0089)* volume of conductor (copper). The volume of copper is the same as that of the calculated cylinder. Bottom area * height (that is, the length of the conductor). To calculate the area of copper wire, the diameter of copper wire must be measured first.
The diameter of the copper wire is 1.772, so the square of the area =( 1.772 divided by 2) *3. 14=2.46.
The area is 2..46* the height is 100* the specific gravity of copper is 0..0089=2. 1894, which is the copper wire weight of this wire.
2. Copper wire weight * copper wire price (55.7 yuan/kg) = 122 yuan. This is the price of copper wire.
3. Cost calculation of PVC insulation: the total weight of wires-the weight of copper = the weight of insulation, multiplied by the price of PVC material (8 yuan/kg) = the price of insulation.
4, plus 5% of the production cost is the cost price of this line.
Note: The calculation method of aluminum core wire is the same as above. The specific gravity of aluminum wire is 0.0027.
Learning the cost calculation method of wire and cable has laid a good foundation for us to buy high quality and low price wire and cable. If the price is too low, there must be something wrong with the wires, because no dealer will do business at a loss. If the price is too high, the dealer will see too much profit. Ha ha!
Fourth, wire and cable quality.
At present, inferior wires on the market all have the problem of cutting corners. 1, the length is not enough; 2, conductor wire drawing (that is, the wire is thick at both ends and thin in the middle); 3, wire material is not up to standard, resistance does not meet the requirements of national standards. The most serious is the copper-clad aluminum conductor, that is, a layer of copper is plated on the aluminum wire, which looks like copper wire, but in fact the current carrying capacity of copper wire is the same as that of aluminum wire. 4, thermal insulation materials can not meet the requirements of national standards. Let's do it one by one, and let the inferior wires show their true colors!
1, conductor length calculation
As shown above:
A number: the number of wires on the horizontal plane.
B number: the number of wires on the hard surface.
C length: the length from the edge of any side to the inner disk (unit meter)
I don't know the disk surface. The meter number of this line =A number ×B number ×C length ×3. 14.
For example, the coil of BV2.5 wire:
Item code: 12
No. B: 16.
C length: 16.5cm, that is, 0. 165m.
Then the length of this line is:12×16× 0.165× 3.14 = 99.47 meters.
The error is within 1 meter.
2. Identification method of copper-clad aluminum and copper-clad copper.
Most copper-clad aluminum wires are soft copper wires, and the identification method is very simple. One end of the copper wire is ignited by the outer flame of the lighter. Because the melting point of aluminum wire is lower than that of copper wire, if it is copper-clad aluminum, the burned part will soon turn to ashes, leaving nothing behind. If it is pure copper, the copper wire will shrink rapidly after burning, and a small ball will always be left on the end of the wire during the shrinking process.
Copper clad copper means copper clad copper. Red copper is oxygen-free copper, and its resistance meets the national standard. Brass is a copper wire with large impurities and secondary annealing. Because the cost of copper is more than 4000 yuan per ton higher than that of brass, some black-hearted manufacturers produce copper-clad copper wires to reduce costs and reap huge profits from them. To identify copper-clad copper, you can cut a small piece of copper wire again with a hacksaw or scissors, and then observe the section yourself, and you will find many small yellow spots that can be distinguished by the naked eye. Furthermore, copper-clad copper is harder than oxygen-free copper wire.
3. Identification method of wire drawing
The drawn wires are indistinguishable in appearance. But the weight is lighter than the national standard line. There is also the simplest method, which is to cut from the middle on the spot and actually measure it. Hmm. How interesting
4, insulation appraisal method
The identification of insulation is professional. It needs to be tested by professional equipment. The simple identification method is to dig by hand, a piece of insulation is inferior PVC or cut a section, make a hard fold, and then put it down, and observe that wrinkles, whitening or cracking are inferior insulation.
Verb (abbreviation of verb) Selection of wire and cable specifications and models.
Choosing the appropriate wire and cable model is the premise of ensuring safe electricity use. When selecting the type of wire and cable, we should consider the purpose, laying conditions and safe range of the wire. When selecting wire and cable specifications, the conditions such as heating, voltage loss, economic current density and mechanical strength should be considered.
According to experience, because of its large load current, the cross section of low-voltage power line is generally selected according to the heating situation, and then its voltage loss and mechanical strength are checked; Low-voltage lighting lines have high requirements on voltage level, so the cross section can be selected according to the allowable voltage loss, and then the heating and mechanical strength can be checked. For high voltage lines, the cross section is selected according to the economic current density, and then the heating conditions and allowable voltage loss are checked; The mechanical strength of high-voltage overhead lines should also be checked.