Precautions in the Manufacturing Process of Low-Voltage Distribution Boxes

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# I. Electrical Safety
- **Insulation Treatment**
- The conductive parts inside the box (such as busbars, wiring terminals of electrical components, etc.) must be reliably insulated from the box body. Qualified insulating materials should be used, such as insulating supports, insulating pads, etc. For example, an insulating partition with a sufficient thickness (generally not less than 10mm) should be installed between the busbar and the side plate of the box body to prevent accidental electric shock.
- For parts where creepage phenomena may occur, sufficient electrical clearance and creepage distance should be ensured. In a humid environment, the requirements for creepage distance are higher. For example, the creepage distance between bare conductors of different phases and between bare conductors and grounded metal should be calculated as not less than 1mm per volt of the rated voltage in a general environment; in a humid environment, this value should be appropriately increased.
- **Grounding System**
- The distribution box must have a complete grounding device. A special grounding terminal should be provided on the box body, and its specifications should meet the requirements of the grounding current. The grounding terminal should be reliably connected to the grounding busbar inside the box, and the contact resistance at the connection point should be as small as possible, generally not exceeding 0.1Ω.
- All equipment inside the box that needs to be grounded (such as electrical components with metal casings, the metal shielding layers of cables, etc.) should be connected to the grounding busbar through yellow-green double-color grounding wires. The cross-sectional area of the grounding wire should be determined according to the rated current and short-circuit current of the equipment to ensure that the current can be quickly introduced into the ground in case of a fault.

### II. Component Selection and Installation
- **Component Selection**
- Select appropriate electrical components according to the design purpose and load characteristics of the distribution box. For example, for a distribution box controlling a motor, suitable capacity contactors and thermal relays should be selected. The rated current of the contactor should not be less than 1.3 times the rated current of the motor, and the setting current of the thermal relay should be accurately adjusted according to the rated current of the motor.
- Select components with reliable quality and in line with relevant standards. Check whether the components have certification marks, such as the CCC certification (China Compulsory Certification), etc. The technical parameters of the components (such as rated voltage, rated current, breaking capacity, etc.) should meet the requirements of the system.
- **Component Installation**
- The installation positions of electrical components inside the box should be convenient for operation, maintenance and overhaul. A certain distance should be maintained between components to facilitate wiring and heat dissipation. For example, the distance between small circuit breakers is generally not less than 20mm to prevent the arcs generated during fault tripping from affecting each other.
- Ensure that the components are installed firmly during installation. Appropriate installation methods should be adopted, such as screw fixation, rail installation, etc. For heavier components, the strength of their installation brackets should be considered to prevent loosening or falling during transportation or operation.

### III. Wiring Technology
- **Wire Selection**
- Select appropriate wires according to the rated current, operating voltage and laying method of the circuit. Generally speaking, the long-term allowable current-carrying capacity of the wire should be greater than the operating current of the circuit. At the same time, factors such as the insulation performance and mechanical strength of the wire should be considered. For example, in a general indoor distribution box, for a control circuit with a current not exceeding 10A, a copper-core insulated wire with a cross-sectional area of 1.5mm² can be selected.
- For circuits with special requirements (such as fire-fighting equipment circuits), fire-resistant and flame-retardant wires may need to be selected, and their colors should comply with relevant standard regulations. For example, red wires are generally used for fire-fighting lines.
- **Wiring Method**
- The wiring inside the box should be neat and aesthetically pleasing, avoiding crossing and confusion. Wire ducts or tying methods can be used to organize the wires. A certain bending radius should be maintained at the bends of the wires, generally not less than 6 times the outer diameter of the wire, to prevent damage to the insulation layer of the wire.
- Wires with different functions (such as power wires, control wires, signal wires, etc.) should be laid separately. When necessary, shielded wires can be used to prevent electromagnetic interference. For example, in a distribution box with PLC (Programmable Logic Controller) control, the signal wires of the PLC should be laid separately from the power wires, and the signal wires can use shielded cables, and the shielding layer should be reliably grounded.

### IV. Heat Dissipation Design
- **Ventilation Measures**
- The distribution box should be designed with reasonable ventilation openings to ensure that the electrical components inside the box are within the normal operating temperature range. The position and size of the ventilation openings should be determined according to the heat generation of the equipment inside the box and the ambient temperature outside the box. Generally speaking, the area of the ventilation openings should not be less than 5% - 10% of the surface area of the box body.
- Dust-proof nets can be installed at the ventilation openings to prevent dust and other impurities from entering the box and affecting heat dissipation and the normal operation of electrical components. The dust-proof nets should be cleaned regularly to maintain good ventilation effects.
- **Temperature Monitoring**
- For distribution boxes with relatively large heat generation, a temperature monitoring device can be considered for installation. When the temperature inside the box exceeds the set value, an alarm signal should be issued in a timely manner to remind the staff to take measures. For example, a temperature sensor can be connected to an alarm, and the alarm temperature can be set at 70°C (the upper limit of the normal operating temperature of general electrical components). When the temperature reaches this value, the alarm will be activated.

### V. Protection Level
- **Box Structure Design**
- Determine the appropriate protection level (IP code) according to the usage environment of the distribution box. For example, for distribution boxes installed outdoors, the protection level is generally required to reach IP54 and above, that is, it can prevent dust and water splashing. The doors, covers and other parts of the box body should be well sealed, and sealing materials such as rubber sealing strips should be used.
- For environments with explosion-proof requirements, the distribution box should adopt an explosion-proof structure design and comply with relevant explosion-proof standards. For example, an explosion-proof type distribution box should ensure that the box body can withstand the internal explosion pressure without damage and prevent the explosion flame from spreading outside the box.
- **Protection of Inlet and Outlet Holes**
- The inlet and outlet holes of the distribution box should be properly protected. Methods such as sealing rubber rings and cable sealing joints can be used to prevent water, dust, etc. from entering the box. For larger inlet and outlet holes, they should be blocked to make them closely fit with the cables or conduits.