How Many Amps Does a 3 HP three-phase Motor Draw at 120V?

Formula (three-phase)

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

1. Convert HP to watts: 3 × 746 = 2,238W
2. Denominator: √3 × 120 × 0.85 × 0.85 = 1.73 × 120 × 0.85 × 0.85 = 150.17
3. Result: 2,238 ÷ 150.17 = 14.9 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. 3 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 14.9 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 3 HP three-phase: 3 HP at 208V 3Φ, 3 HP at 230V 3Φ, 3 HP at 480V 3Φ, 3 HP at 575V 3Φ.
• If this motor is actually single-phase, 3 HP single-phase at 120V is in NEC Table 430.248 with an FLC of 34 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 2,238 W (3 HP × 746). Electrical input at the terminals is higher because no motor is 100% efficient: 2,238 ÷ 0.85 = 2,632.94 W. At $0.17/kWh, running cost is $0.45/hour or $107.42/month at 8 hours/day. Full breakdown at 2,632.94 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:

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.

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