Motor FLA Calculator

Enter motor HP or kW, voltage, phase, efficiency (%), and power factor (%) to get theoretical full-load amps (FLA). Default: 10 HP · 480 V · 3φ · 90% eff · 85% PF → ~11.7 A (NEC Table 430.250 lists 14 A for code sizing).

Quick calculator

Use line-to-line voltage for three-phase. Results update instantly.

Motor power

Phase

Voltage (V)

Advanced calculator

Refine theoretical FLA with nameplate efficiency and power factor. Results still update instantly.

Efficiency (%)

Power factor

About this calculator

See all protection calculators on the hub. This tool returns theoretical FLA from power, voltage, efficiency, and PF—not the NEC table value. Example: 10 HP @ 480 V 3φ, 90% eff, 0.85 PF → 11.7 A; use NEC Table 430.250 (14 A @ 460 V) for branch conductors and OCPD. Next: size cable with the Motor Cable Size Calculator or screen OCPD with the Breaker Size Calculator. Deep dive: motor starting current & protection.

Full-load amps (FLA)

Result explanation

Theoretical FLA: 11.7 A

NEC Table 430.250 (10 HP @ 460 V 3φ) lists 14 A for conductor/OCPD sizing—use the table value for code compliance, not this theoretical result.

Assumptions: Theoretical FLA = (HP × 746) ÷ (√3 × V × Eff × PF). Defaults: 10 HP, 480 V, 3φ, 90% eff, 0.85 PF → 11.7 A. Verify nameplate FLA for overload relays (NEC 430.32).

Continue Your Calculation

After FLA, size the branch circuit conductor at 125% and screen overcurrent protection.

Motor cable size →

NEC 430.250 — Full-load current, 3-phase AC motors

Use these values for branch circuit, short-circuit, and ground-fault protection sizing per NEC 430.6(A)(1). Do not use nameplate FLA for these calculations.

HP	200V	208V	230V	460V	575V
5	17.5	16.7	15.2	7.6	6.1
7.5	25.3	24.2	22	11	8.8
10	32.2	30.8	28	14	11.2
15	48.3	46.2	42	21	16.8
25	80.5	77	70	35	28
50	160	154	140	70	56
100	318	305	280	140	112

Source: NEC Table 430.250 (2023 edition). Values for alternating-current motors, squirrel cage, wound rotor, and synchronous (unity PF). For single-phase motors, see NEC Table 430.248.

Motor FLA formula

Three-phase: FLA = (HP × 746) ÷ (√3 × V × Eff × PF) or FLA = (kW × 1000) ÷ (√3 × V × Eff × PF).

Single-phase: FLA = (HP × 746) ÷ (V × Eff × PF) or FLA = (kW × 1000) ÷ (V × Eff × PF).

Where: 746 = watts per horsepower, √3 ≈ 1.732, Eff = motor efficiency (decimal), PF = power factor (decimal).

Example: 10 HP, 480 V, 3φ, 90% eff, 0.85 PF: (10 × 746) ÷ (1.732 × 480 × 0.90 × 0.85) = 7,460 ÷ 635.4 = 11.7 A. Note: NEC Table 430.250 lists 14 A for 10 HP @ 460V — use the NEC value for code compliance.

Workflow: motor FLA → conductor size → OCPD size → starting current & protection.

Worked motor FLA examples

Example 1 — 10 HP pump motor (480V, 3φ)

Given: 10 HP · 480V · 3φ · 90% eff · 0.85 PF

Calculation: (10 × 746) ÷ (1.732 × 480 × 0.90 × 0.85) = 7,460 ÷ 635.4 = 11.7 A

NEC 430.250: 14 A @ 460V (use for branch circuit sizing). Conductor: 14 × 1.25 = 17.5 A → 14 AWG copper (75°C column = 20 A). OCPD: inverse-time breaker ≤ 250% = 35 A → standard 30 A frame.

Example 2 — 5 HP air compressor (240V, 1φ)

Given: 5 HP · 240V · 1φ · 85% eff · 0.80 PF

Calculation: (5 × 746) ÷ (240 × 0.85 × 0.80) = 3,730 ÷ 163.2 = 22.9 A

NEC 430.248: 28 A @ 230V. Conductor: 28 × 1.25 = 35 A → 10 AWG copper (75°C = 35 A). OCPD: inverse-time ≤ 250% = 70 A → standard 60 A frame. Note: single-phase motors draw higher starting current (LRA ~ 5–7× FLA).

Example 3 — 25 HP conveyor (400V, 3φ, IEC)

Given: 18.5 kW (≈25 HP) · 400V · 3φ · 92% eff · 0.85 PF

Calculation: (18.5 × 1000) ÷ (1.732 × 400 × 0.92 × 0.85) = 18,500 ÷ 541.7 = 34.2 A

IEC standard: Use motor nameplate FLA for protection (IEC 60947-4-1). Conductor: 34.2 × 1.25 = 42.7 A → 10 mm² copper. OCPD: gG fuse ≤ 100 A or MPCB 40–50 A. Starting: DOL starter acceptable for 25 HP at 400V; consider star-delta or soft starter for high-inertia loads.

Frequently asked questions

What is motor FLA?

Full-Load Amps (FLA) is the current a motor draws at rated horsepower, voltage, and frequency under full load. It appears on the motor nameplate and differs from Locked Rotor Amps (LRA/starting current) and Service Factor Amps (SFA).

How do I calculate 3-phase motor FLA?

FLA = (HP × 746) ÷ (√3 × V × Eff × PF). For kW input: FLA = (kW × 1000) ÷ (√3 × V × Eff × PF). Use line-to-line voltage for three-phase.

Should I use nameplate FLA or NEC Table 430.250?

For branch circuit conductor sizing and overcurrent protection, NEC 430.6(A)(1) requires using Table 430.250 (3φ) or 430.248 (1φ) values, not the nameplate FLA. Use nameplate FLA for overload relay sizing per NEC 430.32.

What is the difference between FLA and LRA?

FLA = running current at full load. LRA (Locked Rotor Amps) = current at startup when rotor is stationary, typically 5–7× FLA for NEMA design B motors. LRA determines inrush and voltage drop during starting.

How does efficiency affect FLA?

Lower efficiency means more input power is needed for the same output, increasing FLA. A 95% efficient motor draws ~5% less current than an 85% efficient motor at the same HP and voltage. Premium efficiency (IE3/IE4) motors reduce operating cost and may allow smaller conductors.