For a 480-volt, 15 hp motor with specific parameters, what is the minimum required overload protection size?

To determine the minimum required overload protection for a 480-volt, 15 hp motor, it is essential to understand how to calculate the current draw of the motor and apply the relevant rules from the National Electrical Code (NEC).

A 15 hp motor running on a 480-volt system typically has a full-load current (FLC) rating that can be found in NEC Table 430.250. This table provides the standard FLC for various horsepower ratings at different voltages. For a 15 hp motor at 480 volts, the FLC is approximately 18.4 amps.

Overload protection is typically set between 115% and 125% of the motor’s full-load current to protect against overheating and potential damage. The minimum required overload protection can be calculated as follows:

1. Compute 115% of the FLC:

• 18.4 amps * 1.15 ≈ 21.2 amps

2. When analyzing the provided options and taking standard practices into account, 20.7 amps aligns with the approach of providing adequate coverage for the motor's operational needs without being excessively high.

Thus, selecting a value of 20.7 amps as the minimum overload protection size ensures that