What is the maximum instantaneous trip circuit breaker setting for a 460-volt, 25-horsepower motor?

To determine the maximum instantaneous trip circuit breaker setting for a 460-volt, 25-horsepower motor, you must first consider the full load current of the motor, which is a crucial aspect in selecting the proper circuit protection. For a 25-horsepower motor operating at 460 volts, the full load current can be calculated using the standard full load current tables or formulas based on motor type and service factor.

Typically, a 25-horsepower three-phase motor at 460 volts has a full load current of approximately 30-35 amps. However, when setting up circuit breakers, particularly for motor protection, it is common practice to follow the National Electrical Code (NEC) guidelines, which allow for a 250% multiplier of the full load current for the instantaneous trip setting.

For a motor with a full load current of around 30 amps, multiplying this by 2.5 yields about 75 amps. However, the maximum setting in the context of this question translates to a normalized and standardized breaker rating that can accommodate inrush current without tripping unnecessarily.

In this case, the value of 272 amps correlates to a motor starting current (often roughly 6-8 times the full load current