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The motor's rated output horsepower.
Nameplate horsepower is the motor's mechanical output rating, not its electrical input draw.
The three-phase line-to-line supply voltage.
The motor's NAMEPLATE voltage, not the system's. Motors are rated a step below the distribution they run on, so a machine on a nominal system is usually stamped several per cent lower, and using the system figure understates the full-load current by the same margin. If the nameplate lists two voltages for a dual-wound motor, use the one matching how it is actually connected.
The motor's rated efficiency at full load.
Converts mechanical output power to electrical input power.
The motor's rated power factor at full load.
From the nameplate, at FULL load, which is the only condition that rating describes. A motor's power factor falls away sharply as it is unloaded, so a machine running at a fraction of its rating draws more current than its rating and the load ratio together suggest — which is why an oversized motor costs more to run than a right-sized one doing the same work. A single assumed figure applied to every motor on a site will be wrong in both directions.
Estimated full-load amperage
11.7 A
This is a calculated estimate — for actual motor circuit conductor and overcurrent protection sizing, NEC 430.250 REQUIRES using the tabulated FLA values from NEC Table 430.250, not the motor nameplate current or a calculated value, per code.
They open the calculator with your figures already in it
Three-Phase Motor Full-Load Amperage Calculator: 11.73 A — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Standard three-phase motor FLA formula: FLA = (HP × 746) ÷ (√3 × voltage × efficiency × power factor), derived from the electrical power relationship P = √3 × V × I × PF applied to motor output power converted to input electrical power via efficiency
Inputs used
- Motor Horsepower (HP)
- 10
- Voltage (V, Line-to-Line)
- 480
- Motor Efficiency (%)
- 90
- Power Factor
- 0.85
Confidence note: This is a calculated estimate — for actual motor circuit conductor and overcurrent protection sizing, NEC 430.250 REQUIRES using the tabulated FLA values from NEC Table 430.250, not the motor nameplate current or a calculated value, per code.
What this calculation does not cover
- This is RUNNING current, not starting current. A motor started across the line draws locked-rotor current of roughly five to eight times FLA for the first seconds, fixed by the NEMA code letter on the nameplate, and that inrush is what sets the starter size, the breaker's instantaneous trip point, and how far the voltage dips on everything else in the panel when the motor kicks in. A generator, a soft start or a trip curve chosen from the number on this page will trip on every start.
- Efficiency and power factor are FULL-LOAD figures, and current does not fall in proportion to load. A motor running at half its rated horsepower still carries most of its magnetizing current, so its power factor collapses - 0.85 at full load can be 0.6 or worse at part load - and the measured amps sit well above half of what is computed here. An oversized motor is the usual reason a clamp reading and a calculated figure refuse to agree.
- Assumes rated voltage actually arrives at the motor terminals. On a long feeder the voltage at the motor is lower than the voltage at the panel, and a motor asked for the same torque at lower voltage answers by drawing MORE current, which heats the windings and shortens insulation life. Long runs have to be checked for voltage drop separately; this formula takes whatever voltage you type as arriving intact.
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This result is a specification — 11.7 A — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Standard three-phase motor FLA formula: FLA = (HP × 746) ÷ (√3 × voltage × efficiency × power factor), derived from the electrical power relationship P = √3 × V × I × PF applied to motor output power converted to input electrical power via efficiency
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