1. In a three-phase five-wire system, yellow, green, red, and light blue represent U, V, W, and N respectively. The protective grounding wire is dual-color (PE).
2. During operation, the current in each phase of the transformer should not exceed the rated current; the maximum unbalanced current should not exceed 25% of the rated current. The transformer should be regularly inspected after it is put into operation.
3. In a system powered by the same transformer, protective grounding and protective neutral grounding should not be mixed.
4. The rated voltage of the secondary coil of a voltage transformer is generally 100V.
5. The secondary side of the voltage transformer must not be short-circuited during operation. A short circuit will generate a large short-circuit current, which may burn out the transformer. Therefore, fuses are installed on both the primary and secondary sides of the voltage transformer for protection.
6. One end of the secondary side of a voltage transformer must be grounded. This is to prevent high voltage from the primary side from entering the secondary side when the insulation between the primary and secondary coils breaks down, endangering personal and equipment safety.
7. When a current transformer is operating, the secondary side is close to a short-circuit condition. The rated current of the secondary coil is typically 5A.
8. The secondary side of a current transformer must never be open-circuited during operation.
9. One end of the secondary side of the current transformer must be grounded to prevent high voltage from the primary side from entering the secondary side when the insulation between the primary and secondary coils breaks down.
10. When connecting current transformers, pay attention to the polarity of their primary and secondary coils. my country uses a subtractive polarity marking method for current transformers.
11. During installation, ensure that the wiring is correct and reliable, and do not connect fuses or switches to the secondary side. Even if it is necessary to remove instruments or other devices on the secondary side for some reason, the secondary side must be short-circuited before removal.
12. Low-voltage switches refer to disconnectors, circuit breakers, fuses, etc., below 1KV.
13. The loads controlled by low-voltage power distribution equipment must be clearly separated into different circuits, and it is strictly forbidden to control multiple circuits with one switch or to confuse them.
14. The interlocking devices between low-voltage power distribution equipment and standby generators should operate reliably. It is strictly prohibited to connect standby generators to the power grid without authorization.
15. Insulating mats should be laid on the passageways for operation and maintenance of low-voltage power distribution equipment in all directions, and it is strictly forbidden to pile other items on the passageways.
16. When connecting equipment: connect the equipment first, then connect the power supply.
When disassembling equipment: disconnect the power supply first, then disassemble the equipment.
When connecting the wires: connect the neutral wire first, then the live wire.
When disconnecting wiring: disconnect the live wire first, then disconnect the neutral wire.
17. Low-voltage fuses cannot be used as overload protection for motors.
18. The rated voltage of the fuse must be greater than or equal to the operating voltage of the power distribution line.
19. The rated current of the fuse must be greater than or equal to the rated current of the fusible element.
20. The breaking capacity of a fuse must be greater than the maximum short-circuit current that may occur in the power distribution line.
21. The selection of the rated current of the fuse must meet the normal operating current of the circuit and the starting current of the motor.
22. For short-circuit protection of loads such as electric furnaces and lighting, the rated current of the melt is equal to or slightly greater than the rated current of the load.
23. For a single motor, the rated current of the fuse is ≥ (1.5-2.5) the rated current of the motor.
24. In a power distribution system, the rated current of a fuse should be coordinated between upstream and downstream levels to achieve selective protection. The rated current of the downstream level should be lower than that of the upstream level.
25. Porcelain plug-in fuses should be installed vertically and must use qualified fuse wires. Other copper wires or similar materials must not be used as substitutes for fuse wires.
26. The power input line of the screw-type fuse should be connected to the center terminal of the base, and the output line connected to the load should be connected to the terminal of the screw-type housing.
27. When replacing the molten metal, the electrical equipment must be disconnected first to prevent electric arcing.
28. Fuses should be installed on each phase line. Fuses are strictly prohibited from being installed on the neutral line of a two-phase three-wire or three-phase four-wire circuit.
29. When a fuse is used for isolation purposes, it must be installed at the beginning of the line.
30. The function of a fuse is short-circuit protection. It isolates the power supply and facilitates safe maintenance.
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