How Many Amps Does a 1 HP three-phase Motor Draw at 120V?

Q: What is 1 HP in watts?

1 HP equals 746 watts of mechanical output (1 HP = 746 W). The electrical input at the terminals is higher because no motor is 100% efficient: at 85% efficiency the input is about 877.65 W.

At 120V, 1 horsepower equals roughly 4.97 amps per line of running current on a three-phase circuit. One HP is 746 watts of mechanical output, but motors are not 100% efficient, so the electrical draw is higher. Applying √3 × V_L-L × Eff × PF: 746W ÷ (√3 × 120 × 0.85 × 0.85) = 746 ÷ 150.17 = 4.97 A.

Where you'll find 1 HP motors: garage door openers, small pool pumps, benchtop tools.

1 HP three-phase motor at 120V

4.97 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)877.65 W

Try: 1HP at 120V (3Φ) 3/4HP at 120V (3Φ) 1/2HP at 120V (3Φ) 1.5HP at 120V (3Φ)

Volts

Motor Type

Running Amps (per line)

4.97

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 × 746) ÷ (√3 × 120 × 0.85 × 0.85) = 746 ÷ 150.17 = 4.97 A per line

Convert HP to watts: 1 × 746 = 746W
Denominator: √3 × 120 × 0.85 × 0.85 = 1.73 × 120 × 0.85 × 0.85 = 150.17
Result: 746 ÷ 150.17 = 4.97 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 120V is not a listed three-phase voltage in NEC Table 430.250. The table lists three-phase motors at 200V, 208V, 230V, 460V, and 575V, three-phase power is not typically distributed at 120V, 240V single-leg, 277V, or 400V in the United States. 1 HP is a listed horsepower, but not at this voltage.

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 4.97 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:

Use one of the voltages NEC Table 430.250 actually lists for 1 HP three-phase: 1 HP at 208V 3Φ, 1 HP at 230V 3Φ, 1 HP at 480V 3Φ, 1 HP at 575V 3Φ.
If this motor is actually single-phase, 1 HP single-phase at 120V is in NEC Table 430.248 with an FLC of 16 A.
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 746 W (1 HP × 746). Electrical input at the terminals is higher because no motor is 100% efficient: 746 ÷ 0.85 = 877.65 W. At $0.17/kWh, running cost is $0.15/hour or $35.81/month at 8 hours/day. Full breakdown at 877.65 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 120V per line and PF 0.85:

Efficiency	Amps at 120V (per line)	Watts Consumed	Waste Heat
75%	5.63 A	994.67 W	248.67 W
80%	5.28 A	932.5 W	186.5 W
85%	4.97 A	877.65 W	131.65 W
90%	4.69 A	828.89 W	82.89 W
95%	4.44 A	785.26 W	39.26 W

Other HP Values at 120V (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	0.621 A	off-table	n/a
1/6 HP	0.8281 A	off-table	n/a
1/4 HP	1.24 A	off-table	n/a
1/3 HP	1.66 A	off-table	n/a
1/2 HP	2.48 A	off-table	n/a
3/4 HP	3.73 A	off-table	n/a
1 HP	4.97 A	off-table	n/a
1.5 HP	7.45 A	off-table	n/a
2 HP	9.94 A	off-table	n/a
3 HP	14.9 A	off-table	n/a
5 HP	24.84 A	off-table	n/a
7.5 HP	37.26 A	off-table	n/a
10 HP	49.68 A	off-table	n/a
15 HP	74.52 A	off-table	n/a
20 HP	99.35 A	off-table	n/a
25 HP	124.19 A	off-table	n/a
30 HP	149.03 A	off-table	n/a
40 HP	198.71 A	off-table	n/a
50 HP	248.39 A	off-table	n/a
75 HP	372.58 A	off-table	n/a

Same HP, Other Voltages (three-phase)

speed 1 HP at 208V = 2.87A per line speed 1 HP at 220V = 2.71A per line speed 1 HP at 230V = 2.59A per line speed 1 HP at 240V = 2.48A per line speed 1 HP at 400V = 1.49A per line speed 1 HP at 480V = 1.24A per line

Related Calculations

bolt 878W electrical input to amps at 120V payments 878W running cost

Frequently Asked Questions

How many amps does a 1 HP three-phase motor draw at 120V?expand_more

At the terminals, a 1 HP three-phase motor at 120V draws about 4.97 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.

What branch-circuit context does a 1 HP three-phase motor at 120V typically sit in?expand_more

Three-phase motor branches are not served from residential receptacles in the US. Three-phase power is distributed to commercial and industrial services, and a 1 HP three-phase motor at 120V needs a dedicated three-phase branch circuit sized by an electrician per NEC 430.22 (conductors) and 430.52(C)(1) (short-circuit / ground-fault protection), against the motor nameplate and install conditions.

What does NEC 430.52(C)(1) say about OCP for a 1 HP three-phase motor?expand_more

NEC Table 430.52(C)(1) percentages apply to the table full-load current, and this combination is not listed in NEC Table 430.250. The input for the 430.52(C)(1) math here is the motor nameplate FLC, applied by a licensed electrician with the device-type percentage that matches the install (175% dual-element fuse, 250% inverse-time breaker, 300% non-time-delay fuse, 800% instantaneous-trip breaker).

What is 1 HP in watts?expand_more

1 HP equals 746 watts of mechanical output (1 HP = 746 W). The electrical input at the terminals is higher because no motor is 100% efficient: at 85% efficiency the input is about 877.65 W.

What is locked rotor amps for a 1 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.

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.