1. The influence of electromotive force In order to prevent the effect of electromotive force due to short circuit, the
single core cable must be of sufficient strength
(1) The support is firmly fixed so that it can withstand the electromotive force corresponding to the expected short-circuit current.
2. Special precautions for
high-voltage AC single core cables. High-voltage AC lines should use multi-core cables as much as possible. When
single core cables must be used for circuits with larger operating currents, the following precautions should be taken:
(1) The cable should be unarmored or armored with non-magnetic materials. In order to avoid the formation of circulating currents, the metal shield should be grounded at only one point.
(2) All wires in the same circuit should be placed in the same pipe, conduit or trunking, or all phase wires should be installed and fixed together with wire clamps, unless they are made of non-magnetic materials.
(3) When installing two,
three or four single core cables to form a single-phase circuit, a three-phase circuit or a three-phase and neutral circuit respectively, the cables should be in contact with each other as much as possible. In all cases, the distance between the outer sheaths of two adjacent cables should not be greater than the diameter of one cable.
(4) When a
single core cable with a rated current greater than 250A must be installed close to the steel cargo bulkhead, the gap between the cable and the boom should be at least 50mm. Except for cables that belong to the same AC circuit that are laid in a three-lobe shape.
(5) Magnetic materials should not be used between the
single core cables of the same group. When the cables pass through the steel plate, all the wires of the same circuit should pass through the steel plate or stuffing box together, so that there is no magnetic material between the cables, and The gap between the cable and the magnetic material should not be less than 75mm. Except for cables that belong to the same AC circuit that are laid in a three-lobed shape.
(6) In order to make the impedance of a three-phase circuit of considerable length composed of a
single core cable with a conductor cross-section equal to or greater than 185mm2 approximately equal, each phase should be transposed once at a gap not exceeding 15m. Alternatively, the cable can be laid in a trilobal shape. When the cable laying length is less than 30m, it is not necessary to take the above measures.
(7) When several single core cables are used in parallel in each phase of the circuit, all cables should have the same path and the same cross-section. And cables belonging to the same phase should be laid alternately with cables of other phases as much as possible to avoid uneven current distribution.
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