What is the maximum size of the 3-pole circuit breaker allowed in a 120/240-volt panelboard for a motor feeder?

In the context of motor feeder applications, the National Electrical Code (NEC) provides specific guidelines regarding circuit breakers. For a 120/240-volt panelboard serving a motor feeder, the maximum size of a 3-pole circuit breaker is contingent upon the motor's full-load current and the allowable ampacity outlined in the NEC.

The largest permissible size for a 3-pole circuit breaker in this specific setup is generally limited to 350 amps. This is a result of both safety considerations and the ability to accommodate typical applications without exceeding the panelboard’s design limitations.

When evaluating the values represented in the choices, 350 amps aligns with the standards for protecting the feeder circuit while ensuring compliance with code regulations. Therefore, this value is recognized as the maximum size permissible for the breaker in the intended application, making it the most appropriate choice among the options provided.