Most Network installers know that the general transmission distance of a CAT5E Ethernet Cable can only be 100 meters, and stable transmission cannot be guaranteed for data more than 100 meters, and the packet is severely dropped or does not work at all. But why it can only be 100 meters, few people have said.
Before talking about this issue, we must first clarify a concept. This 100 meters refers to the distance between two electrical ports of directly connected network equipment, including network modules and patch panels.
We know that the digital mode transmits data using binary, that is, 0 and 1. When the network cable transmits data, there is a current passing through it will generate a voltage, and we transmit data through voltage. We define a voltage between 5 volts and 15 volts as "1", and a voltage between -5 volts and -15 volts as "0". Transmitting different voltages means different numbers in the binary system. We use voltages from -3 volts to 3 volts as a sign of abandonment. From 3 to 5, there is a 1 point tolerance space, because it will be discarded when it reaches -3 or 3, so it cannot be counted as 2.
Based on the above principles, we can roughly calculate how long the Ethernet Cable can be. Everyone knows that the national standard network cable has a core diameter of 0.5mm, and a single wire area is 0.1965 square millimeters. The resistivity of the copper wire at room temperature is about 0.0175, and the characteristic impedance of the network cable is |Z|=100Ω.
Now according to this formula, resistance = resistivity multiplied by the length of the wire/the area of the wire, we can calculate that the longest length of the network cable is 112 meters.
Of course, this is a simple conversion, not very rigorous. In fact, the speed of data transmission and the length of the network cable (the longer the parallel capacitance, the larger the capacity), the slower the speed, and the bending and pressing of the Ethernet Cable will affect the actual length. Under consideration, the two-end jumper in the actual project and the redundancy of the future line aging, so try not to exceed 90 meters, especially when it comes to POE wiring, it is necessary to leave more margin.