How Many Amps Does a 1/4 HP three-phase Motor Draw at 575V?
A 1/4 HP three-phase motor at 575V draws approximately 0.2592 amps per line during normal operation (85% efficiency, PF 0.85). This HP and voltage combination is outside NEC Table 430.250, so there is no code-authoritative LRA multiplier for branch-circuit sizing; refer to the motor nameplate for both running current and startup characteristics.
Common applications for 1/4 HP motors: small pool pumps, light-commercial fans, booster pumps.
Use this citation when referencing this page.
Use the running amps for metering and energy calculations. For branch-circuit sizing, AC motors use the NEC Table 430.248 / 430.250 full-load current under NEC 430.6(A)(1); DC motors use the motor nameplate full-load current under NEC 430.6(A)(3), with Table 430.247 as the reference. Three-phase current is shown per line on a balanced circuit.
Formula (three-phase)
I(A) = (HP × 746) ÷ (√3 × VL-L × Eff × PF)
- Convert HP to watts: 1/4 × 746 = 186.5W
- Denominator: √3 × 575 × 0.85 × 0.85 = 1.73 × 575 × 0.85 × 0.85 = 719.56
- Result: 186.5 ÷ 719.56 = 0.2592 amps per line
Three-phase current is per line on a balanced circuit. Voltage is line-to-line; the √3 factor comes from the three-phase vector geometry, not a round-trip doubling.
NEC Reference Values
This section lists the Code reference numbers a motor branch circuit is sized from. Final conductor, breaker, disconnect, and overload selection is an install decision a licensed electrician makes against the motor nameplate, the actual install conditions, and the applicable NEC articles, not a decision a conversion page can make for you.
Off-Table: No Code-Anchored Sizing
This combination is off-table because 1/4 HP is not a listed horsepower rating in NEC Table 430.250. The table lists discrete HP values (for three-phase: 1/2, 3/4, 1, 1½, 2, 3, 5, 7½, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, and on up), and 1/4 HP falls between listed values. 575V itself is a standard three-phase voltage in the table.
Per NEC 430.6(A)(1) Exception, when a motor rating falls between listed HP values, the next higher listed HP is used for sizing. For 1/4 HP, that means looking at 0.5 HP in the table.
Because there is no table FLC to anchor the NEC 430.22 conductor and 430.52(C)(1) OCP math, this page deliberately does not show branch-circuit sizing values for this variant. Multiplying the 0.2592 A calculated running current by 125% or 250% would produce numbers that look authoritative but are not what the code requires.
What to do instead:
- Apply NEC 430.6(A)(1) Exception and size from the next higher listed HP: 0.5 HP three-phase at 575V. The table FLC shown on that page is the Code-authoritative number for your 1/4 HP branch circuit.
- Pull the motor nameplate FLC and have a licensed electrician apply the 430.22 (conductor) and 430.52(C)(1) (OCP) rules against that number. NEC 430.6(A)(1) Exception permits using the next-higher listed HP where the motor rating is between table values; your inspector may also accept nameplate-based sizing for unusual HP ratings.
Operating Cost
Motor mechanical output is 186.5 W (1/4 HP × 746). Electrical input at the terminals is higher because no motor is 100% efficient: 186.5 ÷ 0.85 = 219.41 W. At $0.17/kWh, running cost is $0.04/hour or $8.95/month at 8 hours/day. Full breakdown at 219.41 W.
Amps by Motor Efficiency (three-phase)
Motor efficiency directly affects amp draw. A more efficient motor draws less current for the same HP output. Values below are the calculated three-phase running current at 575V per line and PF 0.85:
| Efficiency | Amps at 575V (per line) | Watts Consumed | Waste Heat |
|---|---|---|---|
| 75% | 0.2937 A | 248.67 W | 62.17 W |
| 80% | 0.2754 A | 233.13 W | 46.63 W |
| 85% | 0.2592 A | 219.41 W | 32.91 W |
| 90% | 0.2448 A | 207.22 W | 20.72 W |
| 95% | 0.2319 A | 196.32 W | 9.82 W |
Other HP Values at 575V (three-phase)
Running current is the calculated three-phase draw per line at 85% efficiency and 0.85 PF (a conversion from HP under those assumptions, not a measured value). NEC Table FLC is the value from NEC Table 430.250 used for branch-circuit conductor and OCP sizing under NEC 430.6(A)(1). LRA is estimated at 5-7× the NEC table FLC; rows outside the table show n/a because there is no code-authoritative LRA basis for that HP/voltage/phase combination. Row links open each result page in three-phase mode.
| HP | Running Amps (calculated) | NEC Table 430.250 FLC | LRA Estimate (5-7× FLC) |
|---|---|---|---|
| 1/8 HP | 0.1296 A | off-table | n/a |
| 1/6 HP | 0.1728 A | off-table | n/a |
| 1/4 HP | 0.2592 A | off-table | n/a |
| 1/3 HP | 0.3455 A | off-table | n/a |
| 1/2 HP | 0.5184 A | 0.9 A | 4.5-6.3 A |
| 3/4 HP | 0.7776 A | 1.3 A | 6.5-9.1 A |
| 1 HP | 1.04 A | 1.7 A | 8.5-11.9 A |
| 1.5 HP | 1.56 A | 2.4 A | 12-16.8 A |
| 2 HP | 2.07 A | 2.7 A | 13.5-18.9 A |
| 3 HP | 3.11 A | 3.9 A | 19.5-27.3 A |
| 5 HP | 5.18 A | 6.1 A | 30.5-42.7 A |
| 7.5 HP | 7.78 A | 9 A | 45-63 A |
| 10 HP | 10.37 A | 11 A | 55-77 A |
| 15 HP | 15.55 A | 17 A | 85-119 A |
| 20 HP | 20.73 A | 22 A | 110-154 A |
| 25 HP | 25.92 A | 27 A | 135-189 A |
| 30 HP | 31.1 A | 32 A | 160-224 A |
| 40 HP | 41.47 A | 41 A | 205-287 A |
| 50 HP | 51.84 A | 52 A | 260-364 A |
| 75 HP | 77.76 A | 77 A | 385-539 A |