Power cables are generally categorized as single-core, two-core, and three-core cables. Single-core cables have only one conductor within a single insulation layer, while two-core cables have two conductors within a single insulation layer. Both types have their advantages and disadvantages. For example, single-core cables can be used for long runs, control circuits with high operating currents, underwater installations, to avoid or reduce the need for intermediate connections, or when single-core cables offer better overall safety features than multi-core cables.
Which is better: multi-core or single-core cables?
1. In terms of current flow, multi-core cables of the same cross-sectional area carry significantly greater current than single-core cables, posing a greater load.
2. In terms of electrical losses, single-core cables are directly grounded at both ends, and the metal shield may generate circulating currents that can reach the cable's current carrying capacity, wasting energy and causing losses. Multi-core cables generally have three cores because, during operation, the sum of the currents flowing through the three cores is zero, resulting in virtually no induced voltage across the metal shield.
3. From a cost perspective, single-core cables are cheaper than multi-core cables of the same cross-sectional area, with multi-core cables being slightly more expensive.
4. From an installation perspective, single-core cables are stiffer when threading through conduit, while multi-core cables are more flexible and easier to route.
Differences between Single-Core and Multi-Core Cables
2-core Cable: When the neutral conductor of a 1kV or lower power supply is directly grounded, a 2-core cable should be used for single-phase control circuits. When the maintenance line and neutral point share the same conductor, a 2-core cable should be used. For control circuits that can be powered by DC, a 2-core cable is recommended.
3-core Cable: When the neutral conductor of a 1kV or lower power supply is directly grounded, a 3-core cable should be used for single-phase control circuits. When the maintenance line and neutral point are separate, a 3-core cable is recommended.
4-core cable: 4-core cables (3+1 cables) of 1kV and below. The fourth core not only serves as grounding protection but also carries the unbalanced current and short-circuit capacity of the power supply system. Its size is determined by the unbalanced current and short-circuit capacity, but generally should not be less than 1/2 of the phase conductor.
5-core cable: 3-phase, 4-wire distribution system systems of 1kV and below. For electrical equipment distribution lines with high safety requirements, as well as communications centers and automated machinery that require both power safety and anti-interference grounding, a TN-C distribution system with 5 copper core cables is recommended. This system has separate protective conductors (PE) and neutral conductors (PN). The cable core cross-section is generally 3 large and 2 small, 4 large and 1 small, or 5 large.
The difference between 4-core and 3+1-core cables: For 1kV and lower three-phase, four-wire distribution systems, when the mains and neutral points share the same conductor, 4-core cables should be used. Do not use a 3-core cable plus a single-core cable to form a single circuit, or even use the 3-core cable's metal sheath or armored cable layer directly as the neutral point. Otherwise, when the three-phase currents are unbalanced, the operation will be equivalent to that of a single-core cable, easily causing DC interference.
The above explains the difference between single-core and multi-core cables. I believe everyone has a general understanding of the differences and advantages of the two. There is no absolute standard; it depends on the specific application environment. Multi-core cables offer better high-frequency performance, flexibility, and ease of installation and wiring, but they are more expensive. Single-core cables, on the other hand, are less expensive and are also used in certain environments.
