In a control circuit for a three-phase motor starter, where is one side of the NC overload relay contacts connected?

• A. Line 1
• B. Line 2
• C. Line 3
• D. Ground

Answer: (B)

In a control circuit for a three-phase motor starter, one side of the normally closed (NC) overload relay contacts is typically connected to one of the line inputs, in this case, Line 2. This configuration is essential for ensuring proper functionality and safety in the motor control circuit.

When the motor operates normally, the NC contacts allow current to flow through the control circuit, enabling the motor to run smoothly. If there is an overload condition, the overload relay will open the NC contacts, interrupting the control circuit and shutting down the motor to prevent damage.

Connecting the NC contacts to one of the line inputs (like Line 2) serves to integrate the overload protection directly into the power supply of the motor. This ensures that if an overload occurs, the protection is effective and quickly responds to safeguard the motor from potential damage.

While the other line options or ground connection could technically present different scenarios in a control circuit, the established practice is to wire the NC contacts to one of the line inputs to facilitate immediate interruption in the event of an overload situation. Thus, Line 2 is a logical choice in line with standard circuit design principles.