What size inverse time breaker would be used for a 3-phase 480V 100HP induction motor with a FLC of 124 amps?

In selecting the appropriate size of inverse time breaker for a 3-phase induction motor, it is essential to consider the full load current (FLC) of the motor, which in this case is 124 amps for a 100 HP motor operating at 480V.

The inverse time breaker is typically sized at 125% of the motor's FLC to allow for motor start-up currents, which can be significantly higher than the normal operating current. By applying the 125% rule:

1. Calculate 125% of the FLC:

124 amps x 1.25 = 155 amps.

This value suggests that a breaker rated higher than 155 amps should be selected to accommodate the starting inrush without tripping unnecessarily.

Among the choices provided, a breaker with a rating of 200 amps is the most suitable. It exceeds the calculated 155 amps and provides a buffer for any temporary surges in current that can occur during motor startup.

This selection ensures that the motor operates reliably without nuisance tripping while still providing adequate protection. The other options are either too low or do not provide the necessary safety and performance margin. Therefore, the selection of a 200A inverse time breaker is confirmed as the best