How to Improve the Installation Quality of Distribution Boxes
The construction quality of distribution boxes directly impacts the overall quality level of a project. As the construction unit responsible for electrical equipment installation, it is essential to carry out the finalization, procurement, and installation of distribution boxes in accordance with standards such as the Unified Standard for Construction Quality Acceptance of Building Engineering(GB50300-2001) and the Code for Construction Quality Acceptance of Building Electrical Engineering(GB50303-2002), while also integrating the design requirements from construction drawings and the practical needs of the project. To ensure and enhance installation quality, in addition to selecting reputable manufacturers producing high-quality distribution boxes, the following technical points should be implemented during the installation process:
Selecting the Correct Installation Location. In practice, if the location indicated on the construction drawings is unclear or does not meet the actual site requirements, construction personnel sometimes proceed with installation rigidly according to the drawings without promptly consulting the design unit for modifications. Alternatively, they might arbitrarily change the location without the designer's approval. This often results in the installed location being unsuitable for practical use. Therefore, when determining the installation location, engineering and management personnel should engage in spatial visualization based on the drawings or conduct on-site observations. The final position should be determined considering both practical convenience and aesthetic appeal, without compromising functionality. After preliminarily determining the type and specifications of the distribution box, the relevant technical parameters and usage requirements should be provided to the manufacturer for final confirmation.
Integrating Site Conditions with Design Requirements to Standardize Installation Height. According to standards, the height from the bottom edge of a distribution box to the floor is generally 1.5m, and for distribution boards, it should not be less than 1.8m. However, this height can be adjusted higher or lower appropriately for operational and maintenance convenience, provided design approval is obtained. Crucially, within a single project, especially in the same area (e.g., large spaces like malls, markets, or industrial plants with multiple distribution boxes), the installation height must be consistent.
Ensuring Level and Stable Installation, and Accurate Hole Cutting. The installation of the distribution box must be level and stable. According to inspection standards, the permissible vertical deviation for boxes with a height less than 50cm is 1.5mm, and for boxes 50cm or taller, it is 3mm. The positioning of entry and exit holes for cables also significantly affects quality. Manufacturer-provided holes, especially for surface-mounted boxes, may not suit actual needs. For surface conduit entry, the connection between the conduit and the box must be tight and secure, preventing internal wires from being exposed, and should utilize locknuts. Wire entry holes must be smooth and burr-free; metal panels should be fitted with insulating bushings. The goal is firm, precise, and aesthetically pleasing connections.
Selecting Wire Colors According to Standards. For three-phase four-wire systems used in distribution boxes, the standard wire colors must be followed: Phase A - Yellow, Phase B - Green, Phase C - Red, Neutral wire - Light Blue, Protective Earth wire - Yellow/Green bi-color. The use of Yellow/Green bi-color wire for any other purpose is strictly prohibited.
Arranging Wires Neatly and Tying Them into Bundles for Internal Wiring. When connecting incoming/outgoing wires and internal wiring within the box, construction personnel must be meticulous and precise. The wiring connecting electrical components inside the box should be horizontal, vertical, neat, and aesthetically pleasing. Straight sections of wire should be smooth and straight; the bending radius for curves or corners should be no less than 6 times the outer diameter of the wire. Grouped connections and wire slack should be neatly tied into bundles.
Ensuring Firm and Tight Wire Connections, and Providing Secure Neutral and Earth Terminals. According to standards, connections between wires and component terminals must include spring washers and achieve a firm, tight quality. Furthermore, if protective earth connections inside the box are loose or missing, effective electrical safety is compromised. This can lead to the metal enclosure becoming live during an electrical fault, causing electric shock. All wire connections (input, output, internal) must be precise, firm, and secure against loosening. Creepage distances between conductors must meet standards. The stripping length of insulation should be appropriate, with no core wire exposed. Connections for multiple wires should be crimped tightly, then tinned, and receive a secondary insulation treatment compliant with standards. Additionally, the distribution box must be equipped with complete neutral terminal blocks. Both the box body and the door (if it contains electrical devices) must have secure and reliable protective earth terminals.
Maintaining Cleanliness Inside and Outside the Box, and Clearly Marking Labels. After installation is complete, construction personnel should remove any debris or foreign objects from inside and outside the distribution box, ensuring it is clean. Then, clearly label the purpose and identification number of each meter, switch, fuse, and electrical circuit on the surface of the distribution box.
