In power and information systems, lines and cables are effective carriers for transmitting energy and signals. In the electrical and electronic fields, lines and cables are used to connect two points, playing a key role in power distribution networking and information exchange.
The following content will share the basic knowledge about lines and cables from three aspects: wire and cable types, wire and cable specifications, and wire and cable power calculation. Through in-depth and easy-to-understand information transmission and calculation method analysis, it will help you understand the functions and characteristics of lines and cables, and at the same time provide a useful reference for wire diameters, specifications, and material selection.
Wire structure type
Electrical wiring lines are generally composed of conductors, insulation layers, and protective layers. According to our usage requirements, corresponding wire types can be selected in different places.
1. Indoor branch cables often use plastic copper wire, that is, single-strand conductor + hard plastic insulation layer;
2. The main power supply and distribution lines often use multiple strands of wires, insulation layers, and protective layers;
3. Outdoor low-power wires often use rubber-plastic protective sheathed wires, which include wires, insulation layers, and rubber protective sheaths.
In addition, from the perspective of transmission current and power, it can be divided into twisted pair and parallel line. Twisted pair has the characteristics of shielding interference signals, good flexibility and strong plasticity. Parallel has single core, double core and multi-core forms, and different number of cores can be selected according to actual needs.
There are five common materials for cable core conductors: copper, aluminum, silver, gold, and alloys. With the continuous development of industrial materials, synthetic copper alloys, aluminum alloys, tinned copper, silver-plated copper and other materials have also become new materials for use and promotion. However, copper and aluminum are still the most widely used.
Cable insulation materials; generally there are four types, the first type is plastic: polyethylene, polypropylene, polyolefin, etc.; the second type is rubber: natural rubber, EPDM, butyl rubber, etc.; the third type is paper: cable paper, insulating paper; the fourth type is other types: insulating paint, glass fiber, mica, etc.
Cable diameter specification
The diameter of wires and cables is calculated in square millimeters. The commonly used single-core wire diameter specifications are 0.75mm, 1.0mm, 2.5mm, 4mm, 6mm, 10mm, 16mm, 25mm, 35mm, 50mm, 75mm, 95mm, 120mm, 150mm, 180mm, 240mm, etc. There are 16 types. In addition, according to the core characteristics, they are divided into two types: soft core cables and hard cables.
Multi-core cable refers to a cable that gathers more than 2 wires, such as 3*2.5mm, 5*6mm, 5*10mm, where the first number indicates the number of cores and the second number indicates the core diameter. In addition, we often see 3*75mm+2*50mm and 3*185mm+2*120mm for high-power power supply and distribution. This type refers to a cable with three main core cables and two return cables, a total of 5 wires of different diameters gathered together.
In electrical circuits, regardless of high voltage, low voltage, direct current, or alternating current, cables are distinguished by different colors. The positive pole of direct current is usually represented by red, and the negative pole is usually represented by black. In alternating current, red represents the live wire, blue represents the neutral wire, and yellow-green represents the ground wire. In addition, among the three items of alternating current, yellow represents the live wire of item A, green represents the live wire of item B, red represents the live wire of item C, blue represents the neutral wire, and yellow-green or black represents the ground wire.
Cables can be extended or connected to meet the needs of use. For cables between 0.75mm and below 10mm, winding and cross-winding methods are often used. Cables above 10mm and multi-core cables are often crimped with butt joints. For specific operation methods, you can search for relevant operation instructions, so I will not go into details here.
Cable load current calculation
Combined with the power consumption of electrical equipment, it meets the use requirements. Under the premise that the cable can bear the maximum current load, the power supply is provided safely and stably. The calculation of the load current that the cable can bear is an important manifestation of scientific rigor. In the field of electrical engineering, there has been such a formula: 10 down 5; 100 up 2; 25, 35, 4, 3 boundaries; 70, 95, 2 and a half times. 80% or 90% discount for high temperature in pipes, half for bare wires, and upgrade for copper wires. The meaning is that the front 10, 100, 25, 35, etc. refer to the wire diameter, and the back 5, 2, 4, 3 boundaries refer to the safe current carrying capacity per square millimeter. 80% or 90% discount for pipes and high temperatures means that when encountering similar situations, 80% or 90% discount will be applied. If it is a bare wire, it will be calculated at half the current, and the copper wire will be calculated at an upgraded level.
When calculating line loss, two data parameters are required: resistance and current to obtain the loss data of wires and cables.
The first step is to calculate the line resistance: line resistance R = resistivity * total length / S, where the resistivity of copper is 0.0175 ohm mm2/m, that of aluminum is 0.0283 ohm mm2/m, and S is the cross-sectional area of the cable.
The second is line current calculation. The line current can be obtained on-site using the actual measured value, or using the theoretical value: single-item 220V line current = equipment rated power/220, three-item line current = equipment rated power/rated voltage/1.732/power factor.
Finally, wire loss: single-phase 220V circuit wire loss power = line current square * R, three-phase circuit wire loss power = line current square * 3 * power factor * R.
In conclusion: Lines and cables are important components of power supply systems and electronic circuits. This article provides a comprehensive overview of the above-mentioned wire materials, types, characteristics, current carrying, etc. Mastering the above content lays a good foundation for learning electrical engineering, and it is also the basic essentials that electricians must master. For more electrical knowledge, please exchange and interact!
