HP to amps calculator
For branch-circuit sizing, NEC 430.6(A)(1) says to use the table full-load current, not the nameplate. This tool gives both the table value and a calculated estimate.
Conductor size assumes 75 °C terminals, 30 °C ambient and a short run. The breaker figure is the maximum for a squirrel-cage motor per Table 430.52 (250% of FLC, rounded up to a standard size per 430.52(C)(1) Exception 1). A smaller breaker is fine if the motor starts. Overload protection (430.32) is sized from the nameplate current, usually 115–125%. Have a licensed electrician size and install motor circuits.
Table current vs. calculated current
NEC 430.6(A)(1) says to size motor branch-circuit conductors and short-circuit protection from the full-load current in Tables 430.247–430.250, not from the nameplate and not from a calculation. The tables are deliberately conservative so a replacement motor with a slightly different nameplate still fits the circuit.
The calculated figure uses I = hp × 746 ÷ (η × V × PF) (single-phase) or ÷ (1.732 × V × η × PF) (three-phase). It's useful for estimating energy use, not for sizing.
Three-phase full-load current, NEC Table 430.250 (selection)
| hp | 208 V | 230 V | 460 V | 575 V |
|---|---|---|---|---|
| 1/2 | 2.4 | 2.2 | 1.1 | 0.9 |
| 3/4 | 3.5 | 3.2 | 1.6 | 1.3 |
| 1 | 4.6 | 4.2 | 2.1 | 1.7 |
| 1-1/2 | 6.6 | 6 | 3 | 2.4 |
| 2 | 7.5 | 6.8 | 3.4 | 2.7 |
| 3 | 10.6 | 9.6 | 4.8 | 3.9 |
| 5 | 16.7 | 15.2 | 7.6 | 6.1 |
| 7-1/2 | 24.2 | 22 | 11 | 9 |
| 10 | 30.8 | 28 | 14 | 11 |
| 15 | 46.2 | 42 | 21 | 17 |
| 20 | 59.4 | 54 | 27 | 22 |
| 25 | 74.8 | 68 | 34 | 27 |
| 30 | 88 | 80 | 40 | 32 |
| 40 | 114 | 104 | 52 | 41 |
| 50 | 143 | 130 | 65 | 52 |
| 60 | 169 | 154 | 77 | 62 |
| 75 | 211 | 192 | 96 | 77 |
| 100 | 273 | 248 | 124 | 99 |
| 125 | 343 | 312 | 156 | 125 |
| 150 | 396 | 360 | 180 | 144 |
| 200 | 528 | 480 | 240 | 192 |
Single-phase full-load current, NEC Table 430.248
| hp | 115 V | 230 V |
|---|---|---|
| 1/6 | 4.4 | 2.2 |
| 1/4 | 5.8 | 2.9 |
| 1/3 | 7.2 | 3.6 |
| 1/2 | 9.8 | 4.9 |
| 3/4 | 13.8 | 6.9 |
| 1 | 16 | 8 |
| 1-1/2 | 20 | 10 |
| 2 | 24 | 12 |
| 3 | 34 | 17 |
| 5 | 56 | 28 |
| 7-1/2 | 80 | 40 |
| 10 | 100 | 50 |
For 200 V and 208 V single-phase motors, NEC Table 430.248 notes to increase the 230 V current by 15% and 10% respectively.
Questions people ask
How many amps does a 1 hp motor draw?
Per NEC Table 430.248, a 1 hp single-phase motor draws 16 A at 115 V and 8 A at 230 V. Per Table 430.250 a 1 hp three-phase motor draws 4.2 A at 230 V and 2.1 A at 460 V.
Why use the NEC table instead of the nameplate?
NEC 430.6(A)(1) requires the table full-load current for sizing conductors and short-circuit protection. The nameplate current is used for overload protection (430.32).
How is motor conductor ampacity sized?
NEC 430.22: at least 125% of the table full-load current for a single continuous-duty motor.