Distribution Box 380

A 380V distribution box is typically connected using a three-phase, five-wire system with proper grounding and protective devices to safely distribute power to both 380V and 220V loads.

Wiring Configuration

For a 380V three-phase supply, the distribution box generally uses a five-wire system: three-phase lines (L1, L2, L3), a neutral line (N), and a ground line (PE) (green/yellow) for safety. The phase lines are usually color-coded as red, yellow, and blue, while the neutral is light blue. The incoming supply is connected through a main circuit breaker or isolator switch, and the neutral and ground are connected to their respective terminal blocks inside the box (Hielectrics) .

Load Connections

• Three-phase 380V loads (e.g., motors) are connected across all three phases with an additional ground wire. If local control requires, a neutral may also be connected.
• Single-phase 220V loads are connected using one phase, the neutral, and the ground wire. This ensures proper voltage and safety for lighting or smaller appliances .
• Two-phase 380V equipment (like certain welding machines) uses any two phases plus a ground wire. Grounding is recommended even if sometimes omitted in temporary setups .

Protective Devices

The distribution box should include circuit breakers, fuses, or residual current devices (RCDs) to protect against overcurrent and short circuits. For industrial 380V systems, current transformers (CTs) may be installed for metering, relay protection, or monitoring balanced and unbalanced three-phase currents .

• Single CT can measure one phase or balanced three-phase current.
• Two or three CTs are used for more accurate measurement in unbalanced systems or for energy metering .

Installation Considerations

• The box should be securely mounted on a wall using expansion bolts or embedded wood bricks for smaller units.
• Ensure proper spacing and insulation between incoming and outgoing lines.
• For ungrounded or asymmetrically grounded mains, an isolation transformer with a grounded star point may be required to maintain safety and prevent overvoltage .
• TN or TT mains systems are preferred for industrial 380V connections .

Summary

A 380V distribution box safely distributes three-phase power to various loads by using a five-wire system, proper grounding, and protective devices. Correct wiring ensures that both 380V three-phase and 220V single-phase loads operate safely, while CTs and breakers provide monitoring and protection. Always follow local electrical codes and standards when installing or modifying a distribution box.