How Many Amps Does a 10 HP three-phase Motor Draw at 230V?

Formula (three-phase)

I_(A) = (HP × 746) ÷ (√3 × V_L-L × Eff × PF)

1. Convert HP to watts: 10 × 746 = 7,460W
2. Denominator: √3 × 230 × 0.85 × 0.85 = 1.73 × 230 × 0.85 × 0.85 = 287.82
3. Result: 7,460 ÷ 287.82 = 25.92 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 10 HP three-phase motor at 230V, the table value is 28 A (the 230V column covers 220-240V under 430.6(A)(1)).

The 25.92 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 28 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: 28 × 1.25 = 35 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:

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 28 A (roughly 140 to 196 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.

Operating Cost

Motor mechanical output is 7,460 W (10 HP × 746). Electrical input at the terminals is higher because no motor is 100% efficient: 7,460 ÷ 0.85 = 8,776.47 W. At $0.17/kWh, running cost is $1.49/hour or $358.08/month at 8 hours/day. Full breakdown at 8,776.47 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 230V per line and PF 0.85:

Other HP Values at 230V (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.

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