Cables come in a vast array of specifications and models, each with its own unique characteristics. Different specifications also transmit varying amounts of power. Some are quite similar, such as 3+2 and 4+1, both of which are 5-core cables. So, what's the difference between them? The structural differences between these two specifications actually lead to differences in their uses and performance. Let's take a look at the different meanings of 3+2 and 4+1.
The 3+2 and 4+1 cable specifications indicate that a cable contains 3+2 and 4+1 insulated conductors, respectively. The 3 in a 3+2 cable refers to the three phase conductors (L1, L2, and L3, which are the largest) having the same diameter. The 2 represents the neutral and PE conductors: one conductor connects to the neutral conductor (N, which has a smaller diameter than L1, L2, and L3) and the other conductor connects to the ground conductor (PE, which is also smaller in diameter than L1, L2, and L3). 4+1 cable: The "4" in a 4+1 cable represents three wires of equal diameter and the neutral conductor, while the "1" is the PE ground conductor, which has a different diameter. A 4+1 cable consists of four wires: one for the live wire (L1), one for the neutral (N), and one for the ground (PE). The 3+2 cable is mostly used in power systems where 220V power is less common.
The 4+1 cable is used in 380V+220V systems. Because the 220V neutral conductor is more frequently used in these environments than in the 3+2 cable, the neutral conductor has a higher current carrying capacity and therefore a larger diameter. In this case, regulations require the neutral conductor to have the same diameter as the phase conductor, which is why these two specifications exist. According to GB 3.5.1, for 1kV and below: TN-S grounding system: L1, L2, L3 + PE (protective conductor) + N (neutral conductor).
5-core TN-C grounding system: L1, L2, L3, and PEN (combined into one). 4-core TN-C-S grounding system: L1, L2, L3, and the first half of PEN, the second half of PE and N. In the absence of gas discharge lamps and when significant harmonic currents are present, the neutral conductor can have half the cross-section of the phase conductor. This is the origin of the +1+2 arrangement. Since motors generally lack phase conductors, the 1.3+1 arrangement is often used in balanced three-phase lines.
For example, for three-phase motors. The 2.3+2 arrangement is often used in lines with potentially unbalanced three-phase lines and separate neutral-ground protection, such as when the motor distribution box has a single-phase load. The 3.4+1 arrangement is used in lines where three phases supply a single-phase branch, such as lighting. From an economic perspective, a 3+2 cable with the same phase conductor cross-section is undoubtedly less expensive than a 4+1 cable, as it reduces conductor usage. However, when choosing a cable, not only economic factors should be considered.
Load balancing and the impact of third harmonics on neutral current should also be considered. If the neutral conductor cross-section is too small, a 4P circuit breaker is obviously unsuitable. However, a 3P+1 circuit breaker cannot provide overload protection for the neutral conductor. The 3+2 core structure introduced in the early 1990s cannot meet the requirements. The small cross-section of the neutral conductor causes overload tripping. Currently, the 4-core + 1 grounding core structure is widely used. Design institutes require that the cross-section of the grounding core must not be less than 16mm2, when the cross-section of the phase conductor is greater than or equal to 35mm2.
