Wiring method for the metal plate of the distribution box

The metal plate of a distribution box should be properly grounded, with incoming phase, neutral, and ground wires connected to their respective terminals, following a standardized color-coded wiring system.

Wiring Overview

The wiring of a distribution box typically uses a five-wire system: three-phase lines (A, B, C), one neutral line, and one ground line. The phase lines are usually color-coded yellow, green, and red; the neutral line is light blue; and the ground line is yellow with green stripes. The incoming power is connected to the main breaker or air switch, while outgoing circuits are connected according to load requirements.

Connection Details220

V Load: Connect one phase line, one neutral line, and one ground line. The phase line goes to the breaker, the neutral to the neutral terminal block, and the ground to the grounding terminal block. 380V Load (Three-Phase): Connect three-phase lines plus a ground wire.

If local control is required, the neutral line is also connected. Each line is pressed or screwed into its respective terminal block.

Special Two-

Phase 380V Equipment: Two-phase lines can be connected arbitrarily, with a grounding wire added. The neutral line may be required depending on the control setup.

Grounding the Metal Plate

The metal plate and enclosure of the distribution box must be reliably grounded to prevent electric shock. Connect the protective ground wire to the grounding terminal block, which is then bonded to the metal plate and any metal parts of installed devices. This ensures that any fault current is safely directed to the earth.

Wiring Practices

Use high-temperature resistant copper wires with cross-sectional areas suitable for the load. Ensure neat cable management inside the box, avoiding tangling or contact with sharp edges. Follow color coding standards for easy identification and maintenance.

Perform insulation resistance tests and verify all connections before powering on. Install leakage protectors or residual current devices for additional safety.

Safety and Compliance

Always turn off the power before wiring, and follow local electrical codes (NEC, IEC, or regional standards). Proper grounding, correct wire sizing, and secure connections are essential for long-term safety and reliability. Regular inspections and labeling of circuits help maintain the system and simplify troubleshooting.