The core structure of power cables is divided into single core and multi-core. For cables of equal cross-section, we know that the insulated core specifications are all the same size, but we often encounter cables with the same 5 cores, which is 3+ The use and performance of 2-core and 4+1-core power cables are sometimes different. What are the main differences between them? Let’s introduce the difference between the power cables of these two structures.
Wire structure: The conductor is composed of one or more flexible wires, and the conductor is extruded with an insulating layer.
The structure of the cable: The conductor is composed of one or more wires, and the conductor is extruded with an insulating layer. After squeezing the insulated wire core, it becomes a cable wrapping, metal shielding or armoring, and finally the outer sheath is squeezed, or the outer sheath is directly squeezed on the cabled core.
- Core structure
3+2 and 4+1 indicate the number of insulated cores in a cable. If there are 2 or 3, 3+2, 4+1, 5 insulated cores in a power cable, They are called 2-core or 3-core, 3+2 core, 4+1 core, 5 core specifications.
- The similarities and differences of power cable VV 3+2 core and 4+1 core and selection requirements
Take the power cable VV as an example to illustrate the similarities and differences between the two power cables.
Both 3+2 cable and 4+1 cable are used for low-voltage three-phase five-wire transmission. Under the same external conditions, the difference in current carrying capacity of the two cables is not too large; the raw materials used to make up the product are basically the same.
VV 3+2 core, this line is mostly used for residential entrance wires, and for electrical equipment mostly three-phase loads, or where the three-phase is relatively balanced, the neutral wire current is very small, and the core wire specification is 3+ 2, mostly used in industries, such as factories (most of the equipment is three-phase motors). 3 of the 3+2 cable is the same size as the diameter of the three phase wires and the diameter of this cable is also the largest, 2 is the neutral wire and ground wire, one of which is used to connect the neutral wire (N is the neutral wire , The diameter is smaller than the 3 phase wires), and the other wire is used to connect to the ground wire (PE is the grounding protection wire, and the diameter is smaller than the 3 phase wires).
VV 4+1 core, most of the equipment uses single-phase electricity, and it is prone to three-phase imbalance, which leads to relatively large neutral wire current. At this time, the 4+1 core wire specification can be used for any load circuit. The 4 of the 4+1 cable means that the diameters of the three phase wires and the neutral wire are the same, 1 means the PE ground wire has a single diameter; 4+1 means that a cable consists of 4 wires, one of which is used to connect to the live wire (L1 phase Wire), one wire is used to connect to the neutral wire (N neutral wire), and one wire is used to connect to the ground wire (PE grounding protection wire).
Taking into account economic factors, the cost of a 3+2 cable with the same phase line cross-section is definitely lower than a 4+1 cable, after all, it saves the amount of conductors. However, when selecting, not only economic factors must be considered, but also the influence of load balance and third harmonic on the neutral current. If the neutral cross section is selected smaller, it is obviously not suitable for 4P circuit breakers, but 3P+1 cannot be responsible for the overload protection of the N wire. Therefore, in combination with the above requirements, when designing the 3+2 cable 4+1 cable structure, the ground wire and the middle The cross section of the sex line is preferably half of the cross section of the phase line.