Where is the direct bonding in the terminal box

The direct bonding in a terminal box is located at the protective earth (PE) terminal inside the box, where the motor winding leads connect to the external supply.

Location of Direct Bonding

In a motor terminal box, the direct bonding point is the earth terminal inside the enclosure, which is connected to the motor frame and the protective earthing system . This terminal ensures that any fault current from the motor windings flows safely back to the source, enabling automatic disconnection of supply in case of insulation failure . The PE conductor from the supply cable is connected to this terminal, providing a secure and continuous path for fault currents.

Function of the Terminal Box

The terminal box serves as the interface between the motor's internal windings and the external electrical system. It contains the terminal block, connection links, and the earth terminal . The bonding at the PE terminal inside the box is considered sufficient for fault protection according to IEC standards, as long as the conductor is properly sized and continuous . Some motors may also have a second PE terminal directly on the frame, but this is optional and primarily for convenience or creating a second fault loop; it is not required by IEC 60364-4-41 or IEC 60204-1 .

Summary

• Direct bonding point: PE terminal inside the terminal box.
• Purpose: Connects motor frame to protective earth for fault protection.
• Optional external bonding: Additional frame terminal may exist but is not mandatory.
• Standards compliance: Internal PE connection meets IEC requirements if properly installed . This setup ensures both safety and accessibility for maintenance while maintaining the integrity of the motor's protective earthing system.