First, the definition and classification of cables The […]
First, the definition and classification of cables
The generalized wire and cable is also referred to simply as cable. The narrow sense cable refers to the insulated cable. It can be defined as an assembly of one or more insulated cores, and their respective possible coverings, total protective layers and outer coverings. Cables can also have additional uninsulated conductors.
China's wire and cable products are divided into the following five categories according to their use:
1. Bare wire 2. Winding wire 3. Power cable 4. Communication cable and communication cable 5. Wire and cable for electrical equipment
The basic structure of wire and cable:
1. Conductors Conductor currents, wire and cable specifications are represented by the cross-section of the conductor
2. Insulation External insulation material according to its withstand voltage level
Second, the working current and calculation
Electric (wire) cable operating current calculation formula:
P-power (W); U-voltage (220V); cosΦ-power factor (0.8); I-phase current (A)
P-power (W); U-voltage (380V); cosΦ-power factor (0.8); I-phase current (A)
The safe cut-off of the general copper wire is 5-8A/mm2, and the safe cut-off of the aluminum wire is 3-5A/mm2.
In a single-phase 220V line, the current per 1KW power is about 4-5A, and in a three-phase circuit in which the three-phase load is balanced, the current per 1KW power is about 2A.
In other words, in a single-phase circuit, each 1 mm 2 of copper wire can withstand 1 KW of power load; three-phase balanced circuit can withstand 2-2.5 KW of power.
However, the higher the operating current of the cable, the smaller the safe current per square millimeter.
The allowable safe operating current of the cable is:
Ten out of five (less than ten times five)
One hundred and two (more than one hundred times more than two)
2553 4 (two five times by four or three or five times three)
Two and a half times 7905 (multiplied by 2.5 points for the 70% and 95% lines)
The tube temperature is 80% (varies with temperature, the number of safe currents is multiplied by 0.8 or 0.9)
Copper upgrade calculation (in the same section of the aluminum core of the basis of a rise, such as 2.5 in the copper core is a 2.5 in aluminum core rise, then according to four square mm aluminum core count)
Add half of the bare wire (half the original safe current rating)
Third, the common electricity (line) cable type
Cable specification model meaning:
In the wire type, the letter B indicates the wire, the letter V indicates the polyvinyl chloride in the plastic, and the letter R indicates the cord (the conductor is a large number of filaments twisted together). There is no indication that the copper core symbol or hard line (common single-core conductor) is omitted.
Common cable types:
BV-indicates a single copper core PVC insulated wire without sheathed wire. Applicable to AC voltage 450/750V and below power devices, household appliances, instruments and telecommunications equipment wire and cable.