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Practice question · NEC 430.22
What Is the Branch-Circuit Ampacity for a 3 HP Motor?
The branch-circuit ampacity for a 3 HP motor starts in a table, not on the motor nameplate. The stem gives you the table value, 17A, and 430.22 tells you what to do with it: multiply by 1.25 and size the conductors to the result.
Exam-style question (Sparky QOTD)
A 3 HP, 230V, single-phase motor shows 17A in Table 430.248. The minimum branch-circuit conductor ampacity is ___.
A. 21.25A
B. 17A
C. 25A
D. 20A
Answer: A) 21.25A. 430.22 requires 125% of the Table 430.248 full-load current, and 17 × 1.25 = 21.25A.
Where to Find It
Open your Code book to 430.22 and read it with Table 430.248. Table 430.248 is where the stem found 17A for this 3 HP, 230V, single-phase motor. Section 430.22 then sets the minimum branch-circuit conductor ampacity at 125% of that value. The math is 17 × 1.25 = 21.25A. Two stops, one multiplication, done.
Why 21.25 Amps
The bank note for this question is the key habit: single-phase full-load current lives in Table 430.248, not in the other motor table. The stem names Table 430.248 for a reason. It tells you which value to start with, 17A, so you do not waste time hunting for the current somewhere else.
Next, 430.22 applies the 1.25 factor. Seventeen times 1.25 is 21.25, option A. Option B, 17A, is the table value with no factor applied, so it cannot be the minimum conductor ampacity the section requires. You have to take both steps: get the current from the table the stem names, then apply 430.22.
Tab Table 430.248 in your book and label it for single-phase motors. On test day, matching the motor type to the right table first is what keeps the rest of the question simple.
The Trap
Option B, 17A, traps anyone who finds the table value and stops. Options C and D, 25A and 20A, are round numbers that look like conductor answers but do not match the required math. The question asks for the minimum ampacity, and the Code gives you the exact figure: 17 × 1.25 = 21.25A. Do not round that result into a different answer choice.
Exam Tip
Motor conductor questions follow a pattern: table current first, percentage second. Write both numbers down before you look at the choices. If your two numbers are 17A and 21.25A, the choices sort themselves out. For more motor reps like this, see the 22A motor breaker question.
Keep Drilling
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