The grid base plate of a distribution box must be made of cold-rolled steel with adequate thickness, properly grounded, and designed to support electrical components safely according to IEC 61439 standards.

Material and Thickness

The base plate should be constructed from cold-rolled steel to ensure mechanical strength and durability. For floor cabinets and larger distribution boxes (≥600 mm), a 2.0 mm thick plate is recommended, while smaller boxes (<600 mm) may use 1.5 mm thick plates. For multi-floor installations, the second floor also requires a 2 mm thick plate to maintain structural integrity .

Mounting and Structural Requirements

• The base plate must be securely mounted to the cabinet body using bolts of at least M5 size.
• The back edge of the plate should extend at least 30 mm beyond the box bottom to provide stability .
• If the plate thickness is less than 3 mm, a full-length 40 × 4 mm galvanized flat steel reinforcement should be attached to the back, extending 15 cm beyond each end of the box .
• The plate should support busbars, isolators, and other electrical components without deformation under operational loads .

Grounding and Safety

All metal parts of the distribution box, including the base plate, must be well grounded. Electrical appliances installed on the plate should be connected to the grounding frame using bare copper flexible wire through transparent plastic conduits to ensure reliable earthing .

Compliance with Standards

The design and assembly of the base plate must comply with IEC 61439 / EN 61439, which governs low-voltage switchgear assemblies. This includes:

• Ensuring temperature rise limits are not exceeded to prevent insulation degradation .
• Maintaining physical separation of live parts according to the required form of separation (Form 4 for critical installations) to enhance safety .
• Providing mechanical robustness to withstand short-circuit forces and operational stresses .

Additional Considerations

• The base plate should accommodate phase busbars, incoming and outgoing droppers, and insulating sleeves for phase identification .
• Doors and covers should be lockable, and the plate should allow for easy maintenance and component replacement .
• Arc protection measures, such as arc chutes in isolators, should be integrated to extinguish arcs immediately during operation . By following these specifications, the grid base plate will provide a safe, durable, and compliant foundation for all electrical components within the distribution box, ensuring operational reliability and personnel safety.