1kV and below selection conditions for 1~5 core cables

Single core cable

When the circuit is long, the circuit with large working current or underwater is laid, 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.

Low-voltage DC power supply circuit, single-core cable can be used when needed.

2-core cable

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

For the DC power supply circuit, a 2-core cable should be used.

3-core cable

When the neutral point of the power supply of 1kV and below is directly grounded, the number of cable cores of the single-phase circuit is: when the protection line and the neutral line are independent, a 3-core cable should be used.

4-core cable

A 4-core cable (3+1 cable) of 1kV or less, in which the 4th core is used as a protective ground, it also transmits the unbalanced current and short-circuit current of the power system. Its size is determined by the unbalanced current and the short-circuit current, but generally not less than 1/2 of the phase line.

For the three-phase four-wire low-voltage distribution system 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 the 3-core cable plus the single-core cable should not be combined into a single-loop pipeline, or even directly utilized. A metal sheath or armor layer of a 3-core cable is used as a conduit for the neutral line. Otherwise, when the 3-phase current is unbalanced, it is equivalent to the operating state of the single-core cable, which is likely to cause power frequency interference.

5-core cable

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

Selection of the number of medium and high voltage cable cores

For the choice of 3 to 35kV three-phase power supply loop cable core. When the circuit or cable with large working current is laid under water, 3 single-core cables can be used for each circuit. In addition to the above, 3-core cable should be used. 3-core cable can be used with ordinary package or 3 Single core cable stranded construction type.

For the 110kV three-phase power supply circuit, in addition to laying in the lake, seawater and other places and the cable cross section is small, you can use 3 cores, and each circuit can use 3 single-core cables.

For three-phase power supply circuits above 110kV, three single-core cables should be used for each circuit.

For high-voltage AC single-phase power supply circuits such as electrified railways, two-core cables should be used or two single-core cables should be used for each round.

For high-voltage direct current transmission systems, single-core cables should be used; when laying underwater in lakes, seas, etc., coaxial 2-core cables can also be used.