How Many Amps Does a 1.5 HP three-phase Motor Draw at 240V?

Q: What is 1.5 HP in watts?

1.5 HP equals 1,119 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 1,316.47 W.

A 1.5 HP three-phase motor at 240V draws approximately 3.73 amps per line during normal operation (85% efficiency, PF 0.85). Startup current can be 5-7 times the NEC Table 430.250 FLC (30-42 A) for a few seconds, which affects breaker and wire sizing.

Common applications for 1.5 HP motors: air compressors, well pumps, woodworking tools, small shop equipment.

1.5 HP three-phase motor at 240V

3.73 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 FLC (code sizing base)6 A

Conductor min ampacity (NEC 430.22, 125% of FLC)7.5 A

Electrical input (HP × 746 ÷ efficiency)1,316.47 W

Try: 1HP at 240V (3Φ) 2HP at 240V (3Φ) 3/4HP at 240V (3Φ) 1/2HP at 240V (3Φ)

Volts

Motor Type

Running Amps (per line)

3.73

NEC Table 430.250 FLC (code sizing)

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)

(1.5 × 746) ÷ (√3 × 240 × 0.85 × 0.85) = 1,119 ÷ 300.34 = 3.73 A per line

Convert HP to watts: 1.5 × 746 = 1,119W
Denominator: √3 × 240 × 0.85 × 0.85 = 1.73 × 240 × 0.85 × 0.85 = 300.34
Result: 1,119 ÷ 300.34 = 3.73 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.

NEC Sizing Base: NEC Table 430.250 FLC

Per NEC 430.6(A)(1), motor branch-circuit conductors, switches, and overcurrent protection are sized from the values in Table 430.248 (single-phase) or Table 430.250 (three-phase), not from the motor nameplate and not from a calculated full-load amps. For a 1.5 HP three-phase motor at 240V, the table value is 6 A (the 230V column covers 220-240V under 430.6(A)(1)).

The 3.73 A shown in the hero is the calculated running current at 85% efficiency and PF 0.85, per line on a balanced three-phase circuit. This is a conversion from the nameplate horsepower under those assumptions, not a measured value; a real meter reading depends on the motor's actual efficiency, loading, temperature, and design. Use this figure for energy and metering estimates, and use 6 A as the reference FLC when an electrician walks through NEC 430 against the nameplate.

NEC 430.22 Conductor Rule (reference formula)

NEC 430.22 requires motor branch-circuit conductor ampacity of at least 125% of the Code sizing FLC. As a reference calculation against the NEC Table 430.250 value: 6 × 1.25 = 7.5 A. The selected conductor is taken from NEC Table 310.16 at the applicable termination temperature column, with ambient, bundling, and cable-type adjustments applied by the installer. Motor branch-circuit conductors are exempt from the 240.4(D) small-conductor rule via 240.4(G).

NEC 430.52 Overcurrent Protection (code caps)

NEC Table 430.52(C)(1) gives the maximum rating for motor short-circuit and ground-fault protection as a percentage of the Code sizing FLC. The percentage depends on the device type:

Device Type	Maximum % of Table FLC (430.52(C)(1))
Non-time-delay fuse	300%
Dual-element (time-delay) fuse	175%
Inverse-time circuit breaker	250%
Instantaneous-trip circuit breaker	800%

These percentages are maximum caps, not install picks. A real circuit applies the percentage against the Code sizing FLC for the specific device type, rounds up to a standard size per 430.52(C)(1)(a), and is verified against the motor nameplate and the install conditions by the installer. The elevated percentages exist so short-circuit protection does not nuisance-trip on locked-rotor startup inrush.

Locked Rotor (Startup) Current

During the first 2-5 seconds of startup, a squirrel-cage induction motor typically draws 5 to 7 times the NEC Table 430.250 FLC of 6 A (roughly 30 to 42 A). This is why the 430.52(C)(1) percentages above are so much higher than running current: the short-circuit/ground-fault protective device has to ride through locked-rotor inrush without tripping. Actual LRA is set by the motor's NEMA code letter on the nameplate and should be checked there for a real install.

Current	Amps	Duration
Calculated running current (meter)	3.73 A per line	Continuous at full load
NEC Table 430.250 FLC (Code reference)	6 A	Sizing base, not metered
Locked rotor (typical, 5-7×)	30-42 A	2-5 seconds

Operating Cost

Motor mechanical output is 1,119 W (1.5 HP × 746). Electrical input at the terminals is higher because no motor is 100% efficient: 1,119 ÷ 0.85 = 1,316.47 W. At $0.17/kWh, running cost is $0.22/hour or $53.71/month at 8 hours/day. Full breakdown at 1,316.47 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 240V per line and PF 0.85:

Efficiency	Amps at 240V (per line)	Watts Consumed	Waste Heat
75%	4.22 A	1,492 W	373 W
80%	3.96 A	1,398.75 W	279.75 W
85%	3.73 A	1,316.47 W	197.47 W
90%	3.52 A	1,243.33 W	124.33 W
95%	3.33 A	1,177.89 W	58.89 W

Other HP Values at 240V (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	0.3105 A	off-table	n/a
1/6 HP	0.4141 A	off-table	n/a
1/4 HP	0.621 A	off-table	n/a
1/3 HP	0.8279 A	off-table	n/a
1/2 HP	1.24 A	2.2 A	11-15.4 A
3/4 HP	1.86 A	3.2 A	16-22.4 A
1 HP	2.48 A	4.2 A	21-29.4 A
1.5 HP	3.73 A	6 A	30-42 A
2 HP	4.97 A	6.8 A	34-47.6 A
3 HP	7.45 A	9.6 A	48-67.2 A
5 HP	12.42 A	15.2 A	76-106.4 A
7.5 HP	18.63 A	22 A	110-154 A
10 HP	24.84 A	28 A	140-196 A
15 HP	37.26 A	42 A	210-294 A
20 HP	49.68 A	54 A	270-378 A
25 HP	62.1 A	68 A	340-476 A
30 HP	74.52 A	80 A	400-560 A
40 HP	99.35 A	104 A	520-728 A
50 HP	124.19 A	130 A	650-910 A
75 HP	186.29 A	192 A	960-1,344 A

Same HP, Other Voltages (three-phase)

speed 1.5 HP at 120V = 7.45A per line speed 1.5 HP at 208V = 4.3A per line speed 1.5 HP at 220V = 4.06A per line speed 1.5 HP at 230V = 3.89A per line speed 1.5 HP at 400V = 2.24A per line speed 1.5 HP at 480V = 1.86A per line

Related Calculations

bolt 1,316W electrical input to amps at 240V payments 1,316W running cost cable Wire size for 7.5A at 240V (3Φ) (NEC 430.22 minimum: 125% of 6A NEC Table 430.250 FLC)

Frequently Asked Questions

How many amps does a 1.5 HP three-phase motor draw at 240V?expand_more

At the terminals, a 1.5 HP three-phase motor at 240V draws about 3.73 amps per line at 85% efficiency and 0.85 power factor. For NEC branch-circuit sizing use the NEC Table 430.250 full-load current instead: 6 A.

What branch-circuit context does a 1.5 HP three-phase motor at 240V 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 1.5 HP three-phase motor at 240V 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.

How much does a 1.5 HP motor cost to run?expand_more

Operating cost is based on electrical input, not mechanical HP output. At 85% efficiency, a 1.5 HP motor draws about 1,316.47 W at the terminals. At $0.17/kWh (US residential average, last reviewed April 2026), that is $0.22/hour or $53.71/month at 8 hours/day.

What is 1.5 HP in watts?expand_more

1.5 HP equals 1,119 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 1,316.47 W.

Does motor efficiency affect amp draw?expand_more

Yes. A 1.5 HP three-phase motor at 90% efficiency draws 3.52 A at the terminals versus 4.22 A at 75% efficiency. Higher efficiency means lower running amps and lower electrical input wattage for the same mechanical output.

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.