In a 120/208-volt, 3Ø, 4-wire panel, the maximum size circuit breaker permitted to protect three motors is what amperage?

In a 120/208-volt, 3-phase, 4-wire panel, the selection of the maximum size circuit breaker to protect multiple motors must comply with the National Electrical Code (NEC) guidelines. Specifically, when dealing with three motors, you need to consider not only the individual motor ratings but also the total demand.

According to NEC Article 430, the sum of the full-load currents for the three motors should be calculated. Once you have this total, a fraction of this value is used to determine the size of the circuit breaker. As per NEC guidelines, the circuit breaker's rating must accommodate the starting and operating conditions of the motors, ensuring they are adequately protected without nuisance tripping.

The limit on the circuit breaker size for three motors in this configuration tends to be set at 350 amps in line with NEC allowable calculations for motor circuits. This rating provides sufficient headroom for the starting currents of the motors while ensuring the overall protection of the circuit.

This is why the correct answer is 350 amps—this amperage allows for proper circuit protection in the described system dedicated to motor operation without exceeding the limitations set forth by the NEC.