The power line is a wire that transmits the current. The current mode of current transmission is point to point transmission. The power cord can be divided into AC AC power supply line and DC DC power line according to its usage. Usually, AC power line is wire with alternating voltage of higher voltage. Such wires need unified standard because of high voltage, so that the safety certification can be formally produced. The DC line is basically through the low voltage direct current. Therefore, there is no strict AC line on the security requirements. But for safety reasons, at present, all countries still require unified safety certification.
Performance index of twisted pair wire in power line
For twisted pair lines, the user is most concerned with several indicators that characterize their performance. These indexes include attenuation, near end crosstalk, impedance characteristics, distributed capacitance, DC resistance and so on.

(1) attenuation
Attenuation (Attenuation) is a measure of signal loss along the link. The attenuation is related to the length of the cable, and with the increase of the length, the attenuation of the signal is also increased. Attenuation is used as a unit of "DB" to indicate the ratio of the source signal to the receiver's signal intensity. As the attenuation varies with frequency, the attenuation of all frequencies within the range of application should be measured.
(2) near end crosstalk
The crosstalk is divided into the near end crosstalk and the far end crosstalk (FEXT). The test instrument is mainly the measurement of the NEXT. Because of the loss of the line, the value of the FEXT is less. The loss of the near end crosstalk (NEXT) is to measure the signal coupling from one pair of lines to another in a UTP link. For the UTP link, NEXT is a key performance index, and it is also the most difficult and accurate measurement. With the increase of the frequency of the signal, the difficulty of the measurement will be increased. NEXT does not represent the crosstalk value generated at the near endpoint, it is only the crosstalk value measured at the near endpoint. The value varies with the length of the cable, and the longer the cable is, the smaller the value becomes. At the same time, the signal of the sending end also attenuates, and the crosstalk of the other line pairs is relatively small. Experiments show that only 40 meters in measurement of NEXT is real. If the other end is a 40 meter information socket, it will produce a certain degree of crosstalk, but the tester may not be able to measure the crosstalk value. Therefore, it is best to carry out NEXT measurements at two endpoints. The current tester is equipped with the corresponding equipment so that the NEXT value of the two ends can be measured at one end of the link.
(3) DC resistance
TSB67 does not have this parameter. The DC loop resistor will consume a part of the signal and turn it into heat. It refers to the sum of a pair of wire resistors.
The DC resistance of the 11801 - gauge twisted pair is not more than 19.2 ohms. The difference between each pair can not be too large (less than 0.1 ohms), otherwise the contact point must be checked.
(4) characteristic impedance
Unlike the loop DC resistance, the characteristic impedance includes resistance and impedance inductance and capacitance impedance from 1 to 100MHz, which is related to the distance between a pair of wires and the electrical performance of insulators.
All kinds of cables have different characteristic impedance, and the twisted pair cable has 100 ohms, 120 ohms and 150 ohms.
(5) attenuation crosstalk ratio (ACR)
In some frequency range, the proportion of crosstalk and attenuation is another important parameter to reflect the performance of the cable. ACR is sometimes expressed as a signal to noise ratio (SNR: Signal-Noice ratio).
It is calculated by the difference between the worst attenuation and the NEXT value. The value of ACR is larger, which indicates that the ability of anti-interference is stronger. The general system requires at least 10 decibels.
(6) cable characteristics
The quality of a communication channel is described by its cable characteristics. SNR is a measure of the intensity of the data signal when the interference signal is taken into account. If SNR is too low,
When the data signal is received, the receiver can not distinguish between the data signal and the noise signal, and eventually causes the data error. Therefore, in order to limit the error of the data to a certain extent,
A minimum of acceptable SNR must be defined.
There are 1, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 120, 150, squares, squares, square millimeters.
In addition: such as
VV4X16MM2 is PVC insulated, PVC sheathed copper core cable, 4 core, 16 square per core.
BV1X95MM is a PVC insulated copper core with a cross section of 95 square.
RVV3X2.5MM2--- generally R plus in the back of "multi cored line", plus in front of the general is "ZR", representing flame retardant.
VV is PVC insulated, PVC sheathed cable,
BV is a flat PVC sheathed cable,
RVV is PVC insulated, PVC sheath soft cable.
The later represents a few copper lines extremely cross section.
Usually the copper wire by 1mm2 4~6A through the current calculation, 1mm2 can 5A current is 1.1 kW, and so on; in general, air conditioner with 2.5, with 4 of the lighting cabinet, with 1 on the line.