Wiring method for the main line of the secondary distribution box

The main line of a secondary distribution box is typically wired using a five-wire system: three-phase lines, one neutral, and one protective earth, with careful sequencing and proper connection to breakers and terminal blocks.

Wiring Overview

The incoming main line to a secondary distribution box generally follows a five-wire system: three-phase lines (commonly yellow, green, and red), one neutral line (light blue), and one protective earth line (yellow-green striped) ( ). The wiring sequence is as follows:

• Three-phase lines (L1, L2, L3): Connect to the main isolating switch or general disconnector of the secondary distribution box ( ).
• Neutral line (N): Connect to the neutral terminal block, often routed through the leakage protection device before distribution ( ).
• Protective earth (PE): Connect to the PE terminal block; the PE line should not pass through the leakage protector to avoid unintended tripping ( ).

Connection Steps

1. Main Switch Connection: Lead the three-phase lines from the main isolating switch to the input terminals of the secondary box. Ensure each phase is clearly marked and color-coded ( ).
2. Neutral and PE Wiring: Connect the neutral line to the N terminal of the leakage protector, then to the neutral bus. Connect the PE line directly to the PE bus, ensuring the box door is bonded with braided soft copper wire for safety ( ).
3. Branch Circuit Wiring: From the main breaker, route wires to each branch circuit breaker. Typically, wiring inside the box runs from left (incoming) to right (outgoing) for clarity and organization ( ).
4. Binding and Labeling: Use plastic ties to bind wires neatly, maintaining uniform spacing. Clearly label all lines for voltage, phase, and function to prevent confusion during maintenance ( ).

Safety Considerations

• Inspection: After wiring, perform a safety inspection to check for short circuits, overloads, and proper grounding ( ).
• PE and Neutral Bonding: Ensure the box door and enclosure are reliably connected to the protective earth using braided copper wire ( ).
• Load Considerations: For 220V loads, use one phase, one neutral, and one PE. For 380V three-phase loads, use all three phases plus PE, and include neutral if local control is required ( ).

Summary

Proper wiring of the main line in a secondary distribution box ensures safe, organized, and code-compliant power distribution. Key points include using a five-wire system, correct sequencing of phase, neutral, and PE lines, neat internal wiring, and thorough safety inspection. Following these steps minimizes the risk of short circuits, overloads, and unintended tripping of protective devices.