Final answer:
The minimum ampacity for the feeder serving multiple motors can be calculated by adding up the full load currents of the motors and multiplying it by a factor of 1.25.
Step-by-step explanation:
The minimum ampacity for a feeder serving two motors at 15hp, one motor at 25hp, and one motor at 40hp can be calculated by adding up the full load currents of the motors and multiplying it by a factor of 1.25 to compensate for motor starting currents.
First, we need to find the full load current (FLC) for each motor, using the formula:
FLC = Horsepower / (Efficiency * Voltage)
Assuming an efficiency of 90% and a voltage of 220V, the FLC for each motor would be:
Motor 1 (15hp): FLC = 15 / (0.9 * 220)
Motor 2 (25hp): FLC = 25 / (0.9 * 220)
Motor 3 (40hp): FLC = 40 / (0.9 * 220)
Adding up the FLCs of all the motors:
Total FLC = FLC of Motor 1 + FLC of Motor 2 + FLC of Motor 3
To calculate the minimum ampacity for the feeder, we multiply the Total FLC by 1.25:
Minimum Ampacity = Total FLC * 1.25