What is the maximum size for a 2-pole circuit breaker that can be installed in a 120/240-volt, 3Ø panelboard for a specific motor?

The correct answer indicates that a 100-amp 2-pole circuit breaker can be installed in a 120/240-volt, 3-phase (3Ø) panelboard for a specific motor. This is related to the National Electrical Code (NEC) requirements and the sizing of circuit breakers based on the load they are designed to protect.

In a 3-phase system, particularly for motors, the sizing of circuit breakers can be based on the full load current of the motor and its starting characteristics. A 100-amp breaker allows for adequate protection and operational capacity for many applications, aligning with the typical ampacity values found in NEC tables and manufacturers' specifications.

Selecting the maximum size ensures that the circuit can handle the motor's inrush current without tripping, while also providing necessary overload protection. This capacity helps in minimizing nuisance trips during the start-up phase of the motor while ensuring proper protection under normal operating conditions.

Other sizes, while possibly allowable, may not provide the balance of safety and operation needed for certain motors within the 120/240-volt, 3-phase systems. Thus, for most practical applications, a 100-amp rating is seen as an optimal choice in this context.