What Other Specific Considerations Are Involved in The Design And Wiring Of A Power Distribution Box?

Wiring Requirements for Distribution Boxes

Incoming lines enter from the top, and outgoing lines exit from the bottom; the main circuit is positioned on the left, while the control circuit is on the right. All wiring runs must be perfectly horizontal or vertical.

 

Wiring can be either surface-mounted or concealed. Surface-mounted wiring may utilize sheathed cables, or be routed through conduits or cable trunking. Concealed wiring is predominantly routed through conduits, hidden within structural or decorative walls; typically, the wiring enters and exits from the top, or enters from the top and exits from the bottom.

 

Prior to the installation of distribution cabinets, the control room environment must meet the necessary conditions: all interior finishing work must be complete, and the room must be clean and safe.

 

Upon delivery of the distribution cabinets to the site, organize an unpacking inspection. Check for any signs of deformation or paint damage; verify that all instrumentation components are present and intact; and ensure that spare parts, instruction manuals, and other accessories are complete and undamaged. A detailed unpacking record must be compiled.

 

Based on the layout specified in the construction drawings, sequentially position the switch cabinets onto the foundation steelwork. Once the entire row of cabinets is in place, first align the cabinets at both ends of the row. Then, stretch a taut alignment string across the front of the cabinets at a height corresponding to two-thirds of their total height (measured from the bottom). Align each individual cabinet one by one, using the cabinet face as the primary reference plane. During the alignment process, use 0.5mm shims for adjustment; no more than three shims may be stacked at any single adjustment point.

 

Once the cabinets are positioned and aligned, secure them using the designated mounting bolt holes. Cabinet-to-cabinet connections, as well as connections between cabinets and side panels, must be fastened using galvanized bolts. The high-voltage and low-voltage switch cabinets must be securely welded to the pre-installed angle steel anchors. The exposed floor area within the cable trench (located beneath the cabinets) must be fully covered with checkered steel plates. Additionally, the floor areas immediately in front of and behind the cabinets must be fully covered with insulating mats measuring 1200mm × 10mm (width × thickness).

 

Regarding the alignment tolerances for the switch cabinets: the horizontal deviation between the tops of any two adjacent cabinets shall not exceed 2mm; the overall horizontal deviation across the tops of all cabinets in the row shall not exceed 5mm; the vertical misalignment between the side edges of any two adjacent cabinets shall not exceed 1mm; the overall surface unevenness across the faces of all cabinets shall not exceed 5mm; and the gap between adjacent cabinets shall not exceed 2mm.

 

Once the equipment has been positioned, re-tighten and inspect all internal fasteners-particularly at conductor connection terminals. Upon completion of the internal wiring, use a vacuum cleaner to remove any debris or foreign objects from inside the cabinets, ensuring that both the interior and exterior of the equipment remain clean. Finally, accurately affix labels indicating the equipment designation numbers and circuit numbers. Upon completion of the distribution cabinet installation, the cable trays situated above the cabinets shall be installed. The cable entry and exit openings on the distribution cabinets shall be pre-cut by the supplier in accordance with the specified dimensions; these openings shall be sealed once cable laying is complete. The cable trays shall be reliably grounded to the internal grounding busbar of the cabinet using dedicated grounding cables. At the interface between the cable trays and the distribution boxes (or cabinets), a rubber gasket shall be inserted to protect the conductors and cables. Regarding secondary circuit wiring, all internal secondary circuit connections and associated testing procedures for the distribution cabinets must be completed at the factory prior to shipment. Upon delivery of the distribution cabinet equipment to the site, acceptance inspections shall be organized promptly under the supervision and guidance of the Client's on-site engineers and the project supervisor. It must be ensured that all relevant technical documentation is complete, the cabinet packaging and sealing remain intact, all internal components are present and undamaged, and the wiring connections are secure. Once the distribution cabinets have been installed and securely anchored, insulation resistance tests shall be performed individually on the secondary wiring circuits of each cabinet. These tests shall be conducted using a 500V-rated insulation tester, and the test results are required to exceed 1 MΩ. All secondary circuit control wires and cables shall consist of multi-stranded flexible copper wire; appropriate terminal lugs shall be selected for connection, and-following a tin-plating process-these lugs shall be crimped using specialized crimping tools. A neutral flux agent must be utilized during the tin-plating procedure.