Calculate motor current (amps) from kW or HP, voltage, power factor & efficiency. Supports DC, single-phase & 3-phase AC motors. Free online tool for engineers & electricians. How to Use This Calculator Enter your motor’s power (kW or HP), voltage (V), power factor (PF), and efficiency (η). The tool automatically computes the current (amps) for: Direct Current (DC) motors Single-phase AC motors Three-phase AC motors (most common in industrial applications) Common Applications This calculator helps professionals with real-world tasks such as: Sizing circuit breakers and fuses – Ensure protection devices match motor current draw. Selecting wire gauge – Prevent overheating by choosing correct cable size. Verifying nameplate data – Cross-check manufacturer specs during maintenance. Designing motor control panels – Accurately specify contactors, overload relays, and starters. Energy audits – Estimate operating current for efficiency analysis. Key Formulas The calculator uses industry-standard formulas based on IEC and NEC guidelines: DC Motor: I = P ÷ (V × η) Single-Phase AC: I = P ÷ (V × PF × η) Three-Phase AC: I = P ÷ (√3 × V × PF × η) Note: Power (P) must be in watts (W). If using horsepower (HP), it is automatically converted to watts (1 HP = 746 W). Frequently Asked Questions (FAQ) How many amps does a 10 HP motor draw? It depends on voltage and phase. For example, a 10 HP (7.46 kW), 480V three-phase motor with PF=0.85 and η=0.9 draws about 11.8 amps. What is full load current (FLC)? Full load current is the maximum current a motor draws when operating at rated power and voltage. It’s used to size protective devices per NEC Table 430.250. Why do I need power factor and efficiency? Because motors don’t convert 100% of electrical input into mechanical output. Ignoring PF and η leads to underestimating current—potentially causing tripped breakers or fire hazards. Can I use this for generator sizing? Yes! Calculate motor starting and running current to ensure your generator can handle the load without voltage drop. Does this work for variable frequency drives (VFDs)? This calculator gives fundamental frequency current. VFDs introduce harmonics, so actual current may differ. Use for initial estimates only.

Estimate motor output power in kW or HP from amps, voltage, PF, and efficiency—no nameplate needed. Works for single & three-phase motors. Why Use This Tool? Identify unknown motor size when the nameplate is missing, damaged, or painted over Verify if a motor matches its documented specifications during commissioning Estimate actual mechanical load during energy audits or preventive maintenance How It Works The calculator first determines electrical input power, then applies motor efficiency to estimate mechanical output power: Direct current: Pout = Pout = V × I × η Single-phase: Pout = V × I × PF × η Two-phase: Pout = V × I × PF × η Three-phase: Pout = √3 × V × I × PF × η Results are displayed in both kW and horsepower (HP), where 1 HP ≈ 0.746 kW. Example Calculations Direct current: Pout = √3 × 400 × 10 × 0.85 × 0.90 ≈ 5,450 W = **5.45 kW** HP = 5.45 ÷ 0.746 ≈ **7.3 HP** Three-phase motor: 400 V, 10 A, PF = 0.85, η = 90% → Output ≈ 5.45 kW (7.3 HP) Two-phase: Pout = 230 × 5 × 0.80 × 0.80 = 736 W = **0.74 kW** HP = 0.74 ÷ 0.746 ≈ **1.0 HP** Single-phase motor: 230 V, 5 A, PF = 0.80, η = 80% → Output ≈ 0.74 kW (1.0 HP) Important Notes Use typical estimates if exact values are unknown: PF ≈ 0.8–0.9, Efficiency ≈ 85–95% (for motors under load) Measure current at full or known load—idle or light-load readings will underestimate true power This tool estimates mechanical output power, not electrical input from the grid Typical Applications Industrial maintenance teams identifying legacy motors Energy auditors assessing motor system efficiency Facility engineers verifying replacement motor compatibility Contractors troubleshooting HVAC or pump systems on-site Technical educators demonstrating real-world motor performance Who Should Use This Tool? Maintenance Technicians – Quickly assess motor health and sizing in the field Plant Engineers – Validate motor performance during system upgrades Energy Consultants – Support energy-saving recommendations with real data Electricians – Confirm motor specs before rewiring or protection setup Facility Managers – Plan capital budgets for motor replacements Technical Basis & Best Practices This calculator implements standard IEEE and IEC methodologies for estimating motor output power from operational parameters. For best accuracy: Use a calibrated clamp meter to measure current Measure line-to-line voltage under load If PF is unknown, assume 0.85 for three-phase induction motors If efficiency is unknown, use 90% for motors >5 HP under full load Avoid using this tool for variable frequency drive (VFD)-fed motors unless harmonics are accounted for Frequently Asked Questions How do you calculate motor horsepower from amps? You need four values: voltage, current (amps), power factor, and efficiency. For a three-phase motor, mechanical power (HP) = (√3 × V × I × PF × η) / 746. Our tool does this instantly. Can you determine motor size without a nameplate? Yes. As long as you can measure voltage and current under load—and estimate reasonable PF and efficiency—you can reliably estimate the motor’s output power in kW or HP. What’s the difference between input and output power of a motor? Input power is what the motor draws electrically (kW). Output power is what it delivers mechanically at the shaft (kW or HP). Due to losses (heat, friction), output is always less than input. This tool estimates output power. Why do I need power factor and efficiency? Without power factor, you’d assume all current contributes to useful work—which isn’t true in AC systems. Without efficiency, you’d ignore internal losses. Both are essential for accurate mechanical power estimation.

Calculate your motor’s actual operating voltage from current, power, and PF. Validate against nameplate rating with tolerance checks. Supports single, two, and three-phase AC systems. Input motor parameters to automatically calculate: Operating voltage (V) Supports single-, two-, and three-phase AC systems Real-time calculation from measured current, power, and power factor Voltage validation against typical nameplate ratings (e.g., 230V, 400V, 460V) Key Formulas System Type Formula Direct current U = P / (I × η) Alternating single-phase U₀ = P / (I × cosφ × η) Alternating two-phase U = P / (√2 × I × cosφ × η) Alternating three-phase U = P / (√3 × I × cosφ × η) Parameter Definitions: P: Output mechanical power (shaft power) in kilowatts (kW) I: Line current in amperes (A) cosφ: Power factor (PF), dimensionless, between 0.0 and 1.0 η: Motor efficiency as a decimal (e.g., 90% → 0.90) Example Calculations Example 1: Three-phase motor, I = 10 A, P = 5.5 kW, PF = 0.85 → V = 5.5 / (√3 × 10 × 0.85) ≈ 373.6 V → This is 6.6% below a standard 400V nameplate. May indicate undervoltage or supply issues. Example 2: Single-phase motor, I = 5 A, P = 0.92 kW, PF = 0.8 → V = 0.92 / (5 × 0.8) = 230 V → Matches common 230V residential rating. Operating within normal range. Frequently Asked Questions Q: Why is my calculated voltage different from the motor’s nameplate? A: The nameplate shows the rated (design) voltage. Actual operating voltage depends on your supply, cable length, and load. Differences within ±5% are generally acceptable per NEMA standards. Q: Can I use this tool to check if a 240V motor will run on 120V? A: No. This calculator determines the actual voltage your motor is seeing based on real measurements. It does not simulate compatibility. Running a 240V motor on 120V typically causes overheating and failure. Q: What if I don’t know the power factor? A: For estimation: – Three-phase induction motors: assume PF ≈ 0.85 at full load – Small single-phase motors: PF ≈ 0.7–0.8 For accuracy, measure with a power analyzer or clamp meter that supports PF. Q: Does this work for DC motors? A: No. DC motors do not use power factor, and this tool is designed for AC systems only. Best Practices for Accurate Results Measure under steady-state load (not startup or idle) Use calibrated instruments that report true RMS power and PF Verify phase balance in three-phase systems Always compare results to the motor’s nameplate voltage Who Should Use This Tool? Maintenance engineers troubleshooting motor overheating or tripping Electricians verifying installation quality after wiring Facility managers auditing power quality across plants Technical students learning real-world motor behavior Important Notes Input data must reflect steady-state (running) conditions — not startup surge Voltage cannot be negative; verify measurement polarity and sensor calibration Use high-precision instruments — many basic clamp meters misread power factor Operating voltage varies with load; measure under typical operating conditions Always compare results to the motor’s nameplate before making operational decisions

Calculate actual motor power factor (cosφ) from output power (kW), voltage (V), current (A), and efficiency. For engineers assessing NEMA-compliant motors under real load conditions. Supports single-phase, two-phase, and three-phase AC systems. Key Formulas Since: Pout = Pin × η Pin = U × I × cosφ (for three-phase: √3 × U × I × cosφ) Therefore: System Type Formula Alternating single-phase cosφ = P / (I × U × η) Alternating two-phase cosφ = P / (I × U × η) Alternating three-phase cosφ = P / (√3 × I × U × η) Note: All formulas assume balanced systems. P is output mechanical power in watts (W), η is efficiency as decimal (e.g., 85% → 0.85). Parameter Definitions P (Power): Output mechanical power (shaft power) in watts (W). Enter this value in the “Power” input field. U (Voltage): Line-to-line voltage in volts (V). Enter this value in the “Voltage” input field. I (Current): Line current in amperes (A). Enter this value in the “Current” input field. η (Efficiency): Motor efficiency as a decimal (e.g., 85% → 0.85). Enter this value as a percentage in the “Efficiency” input field; the calculator automatically converts it to decimal form. Real-World Examples Example 1: Three-phase industrial pump motor Nameplate rating: 7.5 kW, PF = 0.85 Field measurement: U = 400 V, I = 12 A, P = 5.8 kW, η = 90% → 0.9 → cosφ = 5800 / (√3 × 12 × 400 × 0.9) ≈ 0.70 → Actual PF ≈ 0.70 vs rated 0.85 → drop of 18% → Insight: At partial load, PF decreases — may increase demand charges and losses. Example 2: Single-phase HVAC compressor Nameplate rating: 1.1 kW, PF = 0.90 Field measurement: U = 230 V, I = 6 A, P = 850 W, η = 80% → 0.8 → cosφ = 850 / (230 × 6 × 0.8) ≈ 0.62 → Actual PF ≈ 0.62 vs rated 0.90 → significant drop → Insight: Low PF may trigger utility penalties in commercial buildings. Frequently Asked Questions Q: Why is my actual power factor lower than the nameplate value? A: Nameplate PF is specified at full load and ideal conditions. In practice, motors often run at partial load, where PF drops significantly—sometimes below 0.7. Q: Does low power factor damage the motor? A: Not directly, but it increases current draw for the same output, leading to higher winding temperatures, reduced lifespan, and larger cable/transformer requirements. Q: Can I estimate PF without measuring active power? A: No. Voltage and current alone give apparent power (kVA), but you need real power (kW) — measured with a wattmeter or power analyzer — to calculate true PF. Q: What’s a “good” power factor for motors? A: ≥0.95: Excellent (modern high-efficiency motors) 0.85–0.95: Good (typical at full load) 0.70–0.85: Acceptable (partial load) <0.70: Poor — consider power factor correction Who Should Use This Tool? Maintenance engineers monitoring motor health Energy auditors assessing power quality Facility managers reducing demand charges Electrical technicians troubleshooting low PF issues Important Notes Measure under stable, representative operating conditions Use a true RMS power analyzer — standard multimeters cannot measure real power accurately Power factor cannot exceed 1.0; values above indicate measurement error PF varies with load: always compare against expected performance at that load level Industrial facilities with PF < 0.9 may face utility surcharges

Use this tool to see how efficiently your motor is running. Enter voltage, current, power factor, and output to check if it’s wasting energy or needs replacement. Motor nameplates list rated efficiency under ideal full-load conditions—but in the field, voltage imbalance, partial load, or aging can significantly reduce real-world performance. This tool uses your actual voltage (V), current (I), power factor (PF), and shaft output power to estimate true motor efficiency and flag anomalies. Enter measured parameters to automatically calculate: Electrical Input Power (kW) – total power drawn from the supply Motor Efficiency (%) – ratio of mechanical output to electrical input Validity Check – alerts if efficiency >100% (indicating measurement error) Supports single-phase, two-phase, and three-phase AC systems with real-time bidirectional calculation (you can also solve for unknown output power). Key Formulas Electrical Input Power (P in): • Single-phase: P in = V × I × PF • Two-phase: P in = V × I × PF • Three-phase: P in = √3 × V × I × PF Efficiency (η): η = (P out / P in) × 100% Real-World Examples & Diagnostics Example 1: Healthy three-phase pump motor Measured: 400 V, 10 A, PF = 0.85, Shaft Output = 5.5 kW → P in = √3 × 400 × 10 × 0.85 ≈ 5.95 kW → Efficiency = (5.5 / 5.95) × 100% ≈ 92.4% Insight: Matches typical IE3 performance at ~75% load. Example 2: Invalid measurement (common pitfall) Measured: 230 V, 5 A, PF = 0.8, Shaft Output = 1.1 kW → P in = 230 × 5 × 0.8 = 0.92 kW → Efficiency = (1.1 / 0.92) × 100% ≈ 119.6% ❌ Diagnosis: Efficiency >100% is physically impossible. Likely causes: – Output power overestimated (e.g., using HP without derating) – Current or PF measured incorrectly – Motor not at steady state Frequently Asked Questions Q: Why is my calculated efficiency higher than 100%? A: This always indicates a measurement error. Common issues include using mechanical horsepower without converting correctly (1 HP = 0.746 kW), misreading current on a clamp meter, or measuring during startup transients. Q: How does load affect motor efficiency? A: Motors are most efficient near full load (75–100%). At 50% load, efficiency can drop by 5–15%. Running a large motor at low load often wastes more energy than using a smaller, properly sized unit. Q: What’s the difference between IE2 and IE3 efficiency? A: IE3 (Premium Efficiency) motors typically operate 2–5% more efficiently than IE2 (High Efficiency) models. For a 10 kW motor running 4,000 hours/year, that gap can save 800–2,000 kWh annually. Q: Can I calculate efficiency without knowing shaft output power? A: Not accurately. While some tools estimate output from nameplate data, true efficiency requires measured mechanical output (via torque sensor or calibrated load test). This calculator assumes you have that value. Important Notes Efficiency cannot exceed 100% — values above indicate input error Use true RMS power analyzers for accurate V, I, and PF readings Always measure under stable, steady-state operating conditions Compare your result to IE-class benchmarks: IE1: ~70–85% IE2: ~85–90% IE3: ~90–96% Low efficiency may signal bearing wear, voltage imbalance, or undersized loading

This free online tool helps you calculate the correct run and start capacitor values needed to operate a three-phase induction motor on single-phase power. It’s ideal for small motors (under 1.5 kW), though note that output power will be reduced to approximately 60–70% of the motor’s original rating. Enter your motor’s rated power, single-phase voltage, and supply frequency to instantly get: Running capacitor value (μF) Starting capacitor value (μF) Supports both kW and horsepower (hp) input Real-time, bidirectional calculation Key Formulas Running Capacitor: C run = (2800 × P) / (V² × f) Starting Capacitor: C start = 2.5 × C run Where: P = Motor power (kW) V = Single-phase voltage (V) f = Frequency (Hz) Example Calculations Example 1: 1.1 kW motor, 230 V, 50 Hz → C run = (2800 × 1.1) / (230² × 50) ≈ 11.65 μF C start = 2.5 × 11.65 ≈ 29.1 μF Example 2: 0.75 kW motor, 110 V, 60 Hz → C run = (2800 × 0.75) / (110² × 60) ≈ 2.9 μF C start = 2.5 × 2.9 ≈ 7.25 μF Frequently Asked Questions (FAQ) Can a 3-phase motor run on single-phase power? Yes—but only small motors (typically under 1.5 kW). You’ll need a run capacitor and a start capacitor, and the motor must be wired in “Y” configuration. Output power drops to about 60–70%. How do I know what size capacitor to use? Use the formula: Crun = (2800 × P) / (V² × f). Our calculator does this automatically based on your inputs. What’s the difference between a start and run capacitor? The start capacitor provides extra torque during startup and must be disconnected once the motor reaches ~75% speed. The run capacitor stays connected during operation to maintain phase shift. What voltage rating should the capacitor have? Always use AC capacitors rated at 400V or higher, even on 110V or 230V systems, to handle voltage spikes during motor operation. Why does motor power decrease on single-phase? Single-phase lacks the rotating magnetic field of three-phase power. Capacitors simulate a second phase, but efficiency and torque are reduced, limiting usable power. Important Safety & Usage Notes Only suitable for small motors (< 1.5 kW) Expected output power: 60–70% of original rating Use capacitors rated for 400V AC or higher The starting capacitor must be automatically disconnected after startup (e.g., via centrifugal switch or relay) Motor must be connected in "Y" (star) configuration—not Delta

Calculate AC induction motor slip (%) and slip in RPM from synchronous speed and rotor speed. Understand slip's role in torque production. For engineers, technicians, and students. How It Works This tool uses the standard slip formula: Slip (%) = (N s – N r) / N s × 100% Slip (RPM) = N s – N r Note: You must provide both Ns and Nr. The calculator does not compute synchronous speed from frequency or poles, nor does it reverse-calculate rotor speed from slip. Example Calculation Input: Synchronous speed = 3000 RPM, Rotor speed = 2850 RPM Output: Slip = (3000 – 2850) / 3000 × 100% = 5% (or 150 RPM) Tip: Synchronous speed can be estimated using Ns = (120 × f) / P, where f = supply frequency (Hz) and P = number of poles. This pre-calculation is required before using this tool. Typical Slip Ranges Motor Type Full-Load Slip Range Fractional HP Motors 5% – 8% Standard Industrial Motors (1–100 HP) 2% – 5% High-Efficiency Motors 1% – 3% High-Slip Motors (e.g., crushers, conveyors) 8% – 15% Important Notes Slip increases with mechanical load. At no-load, it may be as low as 0.5%; at full load, it reaches its rated value. Rotor speed (Nr) is always lower than synchronous speed (Ns) in an induction motor. Prolonged operation with slip >8% may indicate overload, low voltage, bearing wear, or mechanical binding—and can lead to overheating. This tool estimates slip only. It does not model dynamic behavior, harmonics, or VFD effects. Use Cases Verifying expected slip during motor performance checks Supporting troubleshooting when abnormal motor speeds are observed Teaching fundamental induction motor principles in labs or classrooms Providing input data for efficiency or thermal analysis workflows Who Should Use This Tool? Maintenance technicians measuring motor speed in the field Electrical engineers validating motor operating points Students and educators learning about slip and torque production Facility staff documenting motor performance during audits Frequently Asked Questions What is slip in an induction motor? Slip is the difference between the synchronous speed of the stator’s rotating magnetic field and the actual rotor speed. It enables current induction in the rotor, which produces torque. Without slip, the motor cannot generate torque. Is high slip always a problem? Not always. High-slip motors (e.g., for conveyors or crushers) are designed to operate at 8–15% slip. However, if a standard motor shows slip >8% under normal load, it may indicate a problem such as overload or voltage drop. Can I use this tool with VFD-driven motors? Use with caution. VFDs alter frequency and waveform, which affects slip interpretation. This calculator assumes a sinusoidal supply at fixed frequency. For VFD applications, additional harmonic and control considerations apply. How do I find synchronous speed? Synchronous speed (in RPM) is calculated as Ns = (120 × f) / P, where f is the supply frequency (e.g., 50 Hz or 60 Hz) and P is the number of magnetic poles. Example: 4-pole motor at 50 Hz → Ns = (120 × 50) / 4 = 1500 RPM.

Use this free single-phase motor capacitor calculator to quickly find the right starting capacitor value (in μF) for reliable motor startup. Enter your motor’s power, efficiency, voltage, and frequency to get an accurate recommendation—ideal for DIY repairs, maintenance, or motor retrofitting. This tool helps you avoid common mistakes like using oversized capacitors (which cause overheating) or wrong types (which fail prematurely). Only CBB-type AC capacitors rated ≥400V should be used. What This Calculator Provides Starting capacitor value (μF) based on motor specs Supports both 50Hz and 60Hz systems Real-time calculation with unit validation Clear guidance on capacitor type and disconnection Key Formula Starting Capacitor: C = (100,000 × P × η) / (U 0 2 × f) Where: • C = Starting capacitor (μF) • P = Motor rated output power (in watts) • η = Efficiency as a decimal (e.g., 50% → enter 0.5) • U 0 = Single-phase voltage (phase-to-neutral, in volts) • f = Supply frequency (Hz) Example Calculations Example 1: P = 100 W, η = 0.8, U 0 = 22 V, f = 50 Hz → C = (100,000 × 100 × 0.8) / (22 2 × 50) ≈ 330.6 μF Example 2: P = 6000 W, η = 0.5, U 0 = 220 V, f = 50 Hz → C = (100,000 × 6000 × 0.5) / (220 2 × 50) ≈ 124.0 μF Important Notes The starting capacitor is only used during startup and must be disconnected once the motor reaches ~75% speed (via centrifugal switch or relay). Never use electrolytic or DC capacitors—only non-polarized CBB (polypropylene) AC capacitors rated for ≥400V AC. Using a capacitor that’s too large can cause excessive inrush current, winding damage, or switch failure. This calculator applies to capacitor-start single-phase induction motors (not PSC or shaded-pole types). Ensure voltage and frequency match your local supply (e.g., 230V/50Hz or 120V/60Hz). Who Uses This Calculator? Electricians & HVAC Technicians – Quickly size replacement start capacitors during on-site repairs of air conditioners, compressors, or pumps. Maintenance Engineers – Validate capacitor specifications for industrial fans, blowers, or conveyor systems running on single-phase power. DIY Enthusiasts & Hobbyists – Safely restore vintage workshop tools (e.g., lathes, table saws) without guessing capacitor values. Engineering Students – Learn how motor parameters directly influence required capacitance in real-world applications. Common Applications Residential and light-commercial HVAC systems Water pumps and irrigation motors Workshop machinery (drills, grinders, band saws) Farm equipment and small agricultural motors Frequently Asked Questions How do you calculate the start capacitor for a single-phase motor? Use the formula: C (μF) = (100,000 × P × η) / (U₀² × f), where P is the motor’s rated output power in watts, η is efficiency as a decimal (e.g., 0.75 for 75%), U₀ is the single-phase voltage in volts, and f is the supply frequency in Hz. Our calculator automates this—just enter your motor specs to get the correct μF value instantly. What size capacitor do I need for a single-phase motor? The required capacitor size depends on motor power, voltage, and frequency. For example, a 0.75 kW motor at 230V/50Hz needs about 127 μF. Always use the calculated value—never guess or reuse old capacitors without verification. Do all single-phase motors need a start capacitor? No. Only capacitor-start motors require a start capacitor. Permanent Split Capacitor (PSC) and shaded-pole motors use only a run capacitor or no capacitor at all. Check your motor nameplate or wiring diagram to confirm type. How can I tell if my motor start capacitor is bad? Common signs include: motor won’t start (but runs if spun manually), loud humming noise, bulging or leaking capacitor case, or overheating. You can test it with a multimeter in capacitance mode—if the measured value is more than 10% below rated, replace it. Can I use a larger capacitor than recommended? No. An oversized capacitor causes excessive starting current, which can overheat windings, damage the centrifugal switch, or shorten motor life. Always use the calculated “right μF” value for safe and efficient operation. What type of capacitor should I use for a single-phase motor? Only use non-polarized CBB-type (polypropylene) AC capacitors rated for at least 400V AC. Never use electrolytic, DC, or oil-filled capacitors—they are unsafe and will fail quickly under AC motor conditions.

Calculate synchronous and actual motor speed (RPM) per IEC 60034 standards for asynchronous AC motors. Input number of poles, supply frequency (50/60 Hz), and slip to instantly determine shaft speed—essential for design, maintenance, and compliance in industrial and residential applications. Who It’s For Electricians & HVAC Technicians – Verify motor speed during compressor or fan replacement. Maintenance Engineers – Diagnose performance issues in pumps, conveyors, and industrial drives. DIY Enthusiasts – Restore workshop tools (lathes, grinders) with confidence. Engineering Students – Visualize how poles and frequency affect motor behavior. Common Applications Air conditioners and refrigeration compressors Water pumps and irrigation systems Industrial blowers, fans, and conveyor belts Vintage machinery restoration (e.g., table saws, drill presses) Frequently Asked Questions (FAQ) How do you calculate motor RPM? Use the formula: Synchronous Speed = (120 × Frequency) / Poles. Actual speed accounts for slip: Actual RPM = Synchronous Speed × (1 – Slip). What is the RPM of a 4-pole motor at 60Hz? Synchronous speed = (120 × 60) / 4 = 1800 RPM. With typical 5% slip, actual speed ≈ 1710 RPM. Does this work for both 50Hz and 60Hz systems? Yes! Simply select your supply frequency—results auto-adjust for global standards (e.g., 230V/50Hz in Europe, 120V/60Hz in North America). Why does actual speed differ from synchronous speed? Due to slip—the slight lag between rotor and magnetic field rotation in induction motors. Typical slip ranges from 2% to 6% under load. Key Formulas Synchronous Speed (ns) = (120 × f) / P Actual Speed (nr) = ns × (1 – s) Parameter Definitions: ns: Synchronous speed in RPM (revolutions per minute) nr: Actual rotor/shaft speed in RPM f: Supply frequency in hertz (Hz) — e.g., 50 Hz (Europe), 60 Hz (North America) P: Number of magnetic poles (always an even integer: 2, 4, 6, 8, etc.) s: Slip as a decimal (not percentage). For example: • 3% slip → s = 0.03 • 5% slip → s = 0.05 Example Calculation 4-pole motor, 50Hz, 5% slip → ns = (120 × 50) / 4 = 1500 RPM nr = 1500 × (1 – 0.05) = 1425 RPM Typical Motor Speeds Poles 50Hz Sync (RPM) 60Hz Sync (RPM) Actual Speed (≈5% slip) 2 3000 3600 ~2850 / ~3420 4 1500 1800 ~1425 / ~1710 6 1000 1200 ~950 / ~1140 8 750 900 ~712.5 / ~855

This NEC 2023-compliant FLC calculator instantly retrieves Full-Load Current values from official Tables 430.247–430.250—no manual lookup needed. Use it to accurately size circuit breakers, fuses, and conductors for single-, two-, or three-phase motors in accordance with the National Electrical Code. Input your motor parameters to instantly get NEC-compliant FLC values: Supports single-phase, two-phase, and three-phase systems Accepts input in horsepower (HP) or kilowatts (kW) Real-time lookup of FLC in amps (A) Fully compliant with NEC 2023 requirements Common Applications This calculator is used by electricians, engineers, and inspectors for: Sizing overcurrent protection devices (breakers & fuses) per NEC Article 430 Selecting conductor ampacity for branch circuits (wires must be rated ≥125% of FLC) Specifying motor starters and overload relays Preparing electrical plans for code compliance and AHJ review Estimating total load in panel schedules and service calculations How FLC Is Determined Important: NEC Full-Load Current is not calculated by a formula. It is a standardized lookup value from official NEC tables: • Table 430.247: Single-Phase AC Motors • Table 430.248: Single-Phase DC Motors • Table 430.249: Two-Phase AC Motors • Table 430.250: Three-Phase AC Motors Example values from NEC 2023: – Single-phase, 240V, 1 HP → FLC = 4.0 A – Three-phase, 480V, 1 HP → FLC = 2.7 A Frequently Asked Questions Q: Why is NEC FLC higher than my motor’s nameplate current? A: Nameplate current reflects actual test data; NEC FLC uses conservative, standardized values to ensure safety across all motor designs. Code requires using NEC tables — not nameplate ratings — for protection device sizing. Q: Can I use this for VFD-driven motors? A: No. NEC FLC tables apply only to line-powered (across-the-line) motors. Variable frequency drive (VFD) applications require different methods per NEC 430.6(A)(1) Exception. Q: How is kW converted to HP? A: The tool uses the standard conversion: 1 HP = 0.746 kW, as referenced in NEC guidance. Q: Do I need to apply a 125% factor? A: Yes — for continuous-duty motors, conductors must be sized at 125% of FLC (NEC 430.22), but the FLC value itself comes directly from the tables. Important Notes NEC FLC values are typically higher than actual nameplate current Required by code for sizing protective devices and conductors Not applicable to motors powered by VFDs, soft starters, or non-sinusoidal supplies Voltage must be a standard value listed in NEC tables (e.g., 120V, 208V, 230V, 240V, 460V, 480V, 600V) Intended for standard induction motors (typically NEMA Design B)