For a motor rated at 480 Volt - 3-phase, 5 HP, and 4 Amps with a 40°C temperature rise, what should be the overload size?

To determine the appropriate overload size for the motor in question, it's essential to consider the general rule for sizing overloads based on the motor's full-load current and horsepower rating.

For a motor with a specified current rating of 4 Amps and a horsepower of 5 HP, the overload protection is typically set at 125% of the full-load current for motors that have a temperature rise of 40°C. This is a common standard in electrical installation practices to ensure that the motor operates safely without tripping under normal load conditions.

Calculating 125% of the full-load current involves multiplying the rated current (4 Amps) by 1.25.

[

4 Amps \times 1.25 = 5 Amps

]

This value indicates that an overload size of 5 Amps would provide adequate protection for the motor under typical operating conditions without being too sensitive to transient conditions or brief overload situations.

Choosing this overload size is in line with industry practices, which ensures the motor functions effectively while also protecting it from excessive current that could lead to overheating or damage. Thus, the option of an overload size of 5 Amps aligns perfectly with these established guidelines for motor protection.