How Many Amps Does a 1/3 HP three-phase Motor Draw at 575V?

1/3 HP three-phase motor at 575V draws 0.3455 amps per line. Three-phase power is the standard for commercial and industrial motors because it delivers more mechanical output per amp of wire. The amp draw depends on voltage, motor efficiency, and power factor.

Typical 1/3 HP motor applications: small pool pumps, light-commercial fans, booster pumps.

1/3 HP three-phase motor at 575V

0.3455 Amps per line running

Calculated running current at the motor terminals at the assumed 85% efficiency and PF 0.85, per line on a balanced three-phase circuit. This is a conversion from the nameplate horsepower using those assumptions, not a measured value; a real meter reading depends on the motor's actual nameplate efficiency, loading, temperature, and motor design.

NEC Table 430.250 FLCoff-table (see nameplate)

Electrical input (HP × 746 ÷ efficiency)292.52 W

Try: 1/4HP at 575V (3Φ) 1/6HP at 575V (3Φ) 1/2HP at 575V (3Φ) 1/8HP at 575V (3Φ)

Volts

Motor Type

Running Amps (per line)

0.3455

NEC Table 430.250 FLC (code sizing)

off-table

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 × V_L-L × Eff × PF)

(1/3 × 746) ÷ (√3 × 575 × 0.85 × 0.85) = 248.64 ÷ 719.56 = 0.3455 A per line

Convert HP to watts: 1/3 × 746 = 248.64W
Denominator: √3 × 575 × 0.85 × 0.85 = 1.73 × 575 × 0.85 × 0.85 = 719.56
Result: 248.64 ÷ 719.56 = 0.3455 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 1/3 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 1/3 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 1/3 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 0.3455 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 1/3 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 248.64 W (1/3 HP × 746). Electrical input at the terminals is higher because no motor is 100% efficient: 248.64 ÷ 0.85 = 292.52 W. At $0.17/kWh, running cost is $0.05/hour or $11.93/month at 8 hours/day. Full breakdown at 292.52 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%	0.3916 A	331.52 W	82.88 W
80%	0.3671 A	310.8 W	62.16 W
85%	0.3455 A	292.52 W	43.88 W
90%	0.3264 A	276.27 W	27.63 W
95%	0.3092 A	261.73 W	13.09 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

Same HP, Other Voltages (three-phase)

speed 1/3 HP at 120V = 1.66A per line speed 1/3 HP at 208V = 0.9552A per line speed 1/3 HP at 220V = 0.9031A per line speed 1/3 HP at 230V = 0.8639A per line speed 1/3 HP at 240V = 0.8279A per line speed 1/3 HP at 400V = 0.4967A per line speed 1/3 HP at 480V = 0.4139A per line

Related Calculations

bolt 293W electrical input to amps at 575V payments 293W running cost

Frequently Asked Questions

How many amps does a 1/3 HP three-phase motor draw at 575V?expand_more

At the terminals, a 1/3 HP three-phase motor at 575V draws about 0.3455 amps per line at 85% efficiency and 0.85 power factor. This specific HP and voltage combination is outside NEC Table 430.250, so NEC branch-circuit sizing must come from the motor nameplate and a licensed electrician, not from the calculated value above.

Does motor efficiency affect amp draw?expand_more

Yes. A 1/3 HP three-phase motor at 90% efficiency draws 0.3264 A at the terminals versus 0.3916 A at 75% efficiency. Higher efficiency means lower running amps and lower electrical input wattage for the same mechanical output.

How does NEC 430.22 size conductors for a 1/3 HP three-phase motor?expand_more

NEC 430.22 sizes branch-circuit conductors at 125% of the table full-load current, but this HP/voltage combination is not listed in NEC Table 430.250. The correct input for the 430.22 formula here is the motor nameplate FLC, applied by a licensed electrician.

What is locked rotor amps for a 1/3 HP three-phase motor?expand_more

Locked-rotor startup current is typically 5-7 times the NEC table full-load current. Because this HP/voltage combination is not listed in NEC Table 430.250, there is no code-authoritative starting number for the multiplier; refer to the motor nameplate NEMA code letter for the actual LRA value.

What is power factor for motors?expand_more

Motors typically run at PF 0.80-0.85 at full load. At no load, PF drops to 0.30-0.40. Low PF means the wire and breaker carry extra reactive current that does no useful mechanical work, which is why NEC motor sizing uses table FLC (which already accounts for typical PF) rather than a simple watts/volts calculation.

This calculator provides estimates for reference purposes only. Always consult a licensed electrician and verify compliance with the National Electrical Code (NEC) and local electrical codes before performing any electrical work.