What is the minimum conductor size for a branch circuit supplying a motor with the following nameplate information: 115/230V 1Ø 5 hp; The supply is a 2-pole breaker in a 120/240-V 1-ph, 3W panel?

What is the minimum conductor size for a branch circuit supplying a motor with the following nameplate information: 115/230V 1Ø 5 hp; The supply is a 2-pole breaker in a 120/240-V 1-ph, 3W panel?

• A. 3 AWG
• B. 6 AWG
• C. 8 AWG
• D. 10 AWG

Answer: (D)

The concept being tested is sizing motor branch-circuit conductors based on the motor’s full-load current (FLC). For a single-phase motor, the NEC requires the conductors to have an ampacity not less than 125% of the motor’s FLC. You look up the motor’s FLC from its nameplate (or NEC Table 430.248 for the exact rating), multiply by 1.25, and then pick the smallest conductor size that has an ampacity at least that value. A 5 hp motor rated for 230 V single phase has a full-load current of about 16–17 A. 125% of that is roughly 20–21 A. Among the given conductor sizes, 10 AWG copper has an ampacity around 30 A (using typical 75°C ratings), which comfortably covers the 20–21 A requirement. The smaller options would not meet the necessary ampacity within the choices, so the minimum size that fits is 10 AWG.

The concept being tested is sizing motor branch-circuit conductors based on the motor’s full-load current (FLC). For a single-phase motor, the NEC requires the conductors to have an ampacity not less than 125% of the motor’s FLC. You look up the motor’s FLC from its nameplate (or NEC Table 430.248 for the exact rating), multiply by 1.25, and then pick the smallest conductor size that has an ampacity at least that value.

A 5 hp motor rated for 230 V single phase has a full-load current of about 16–17 A. 125% of that is roughly 20–21 A. Among the given conductor sizes, 10 AWG copper has an ampacity around 30 A (using typical 75°C ratings), which comfortably covers the 20–21 A requirement. The smaller options would not meet the necessary ampacity within the choices, so the minimum size that fits is 10 AWG.