A motor rated at 208 V, 3-phase, 15 HP, and 42 Amps requires new overloads due to insufficient initial ratings. What should be the new overload rating?

To determine the appropriate overload rating for a motor, you typically need to consider the full-load current it draws and apply the correct factors based on the motor's type and application. For a 3-phase motor, the formula to calculate the full-load current (FLA) is:

[

FLA = \frac{HP \times 746}{\sqrt{3} \times V \times \text{Efficiency} \times \text{Power Factor}}

]

Assuming general efficiency and power factor values (usually around 0.9 for efficiency and 0.8 for power factor when not specified), we can calculate the FLA for this 15 HP motor.

First, calculate the power in watts:

[

15 , HP \times 746 , W/HP = 11190 , W

]

Now we take into account the voltage and a rough estimation for efficiency and power factor. For a 208 V, 3-phase system, we need to find the FLA:

[

FLA = \frac{11190}{\sqrt{3} \times 208} \approx 31.3 , Amps

]

The next step involves determining the overload protection rating.