What is the minimum ampacity required for branch-circuit conductors for a 115-volt, 3 HP motor with a nameplate current rating of 36.5 amperes?

To determine the minimum ampacity required for the branch-circuit conductors for a 115-volt, 3 HP motor with a nameplate current rating of 36.5 amperes, it is essential to consider both the motor's full-load current and the specific requirements set by the National Electrical Code (NEC).

The nameplate current rating of 36.5 amperes indicates the maximum current the motor will draw under normal operating conditions. However, when selecting conductor sizes for motors, additional factors must be taken into account, including the NEC's requirement to account for potential inrush currents and protection against overheating.

According to NEC guidelines, particularly when dealing with continuous-duty motors, it is common practice to apply an additional 125% rule to the nameplate current rating for branch-circuit conductors. This rule helps ensure that the conductors can safely handle the increased loads and any potential surges.

To apply this, you would calculate 125% of the motor’s full-load current:

1. Calculate 125% of 36.5 amps:

• 36.5 A x 1.25 = 45.625 A.

When selecting conductor sizes, you would typically round up to the next standard ampacity rating