Relationship between Cable Voltage and Core Number

Single-core cable: Longer lines,when the circuit with large working current or underwater laying is used, in order to avoid or reduce the intermediate joint, or the single-core cable has better comprehensive technical economy than the multi-core cable, a single-core cable can be selected. Single core cable can be used in low voltage DC power supply circuit.

2-core cable: When the neutral point of the power supply of 1kV and below is directly grounded, the number of cable cores for a single-phase loop is: when the same conductor is used for the protection line and the neutral line, a 2-core cable should be used. For the DC power supply circuit, the 2-core cable should be used.

3-core cable: When the neutral point of 1kv and its power supply is grounded directly, the cable core number of single-phase circuit is: when the protection line and neutral line are independent, the three-core cable should be adopted.

4-core cable: 1kv and below 4-core cable (3+1 cable), in which the fourth core, in addition to the protection of grounding, but also to transmit the power system in the unbalanced current and short-circuit current. Its size is determined by unbalanced currents and short-circuit currents, but generally not less than 1 / 2 of the phase line.

For three-phase four-wire low-voltage distribution systems of 1kV and below, when the same conductor is used for the protection line and the neutral line, the 4-core cable should be used, and no three-core cable plus a single core cable shall be combined into a single circuit, even the use of 3-core cable metal sheath or armor layer as a neutral line. Otherwise, when the three-phase current is unbalanced, it is equivalent to the running state of the single core cable, which is easy to cause power frequency interference.

5-core cable: Three-phase four-wire low-voltage power distribution system of 1kV and below, some electrical equipment distribution lines with high safety requirements, and some communication centers and automation equipments that must ensure electrical safety and anti-interference grounding should be adopted, it is advisable to use a 5-core TN-C low-voltage power distribution system, the protection line (PE line) and the neutral line (PN line) are independent, and the core cross-sectional area is generally 3 large 2 small or 4 large 1 small or 5 large.

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