⚡ Motor Nameplate Data
85.0%

Check motor nameplate. Typical: 80–92%

0.85

Single-phase motors: 0.75–0.92 typical

⚙️ Additional Settings

Service factor from motor nameplate

🔁 Include Starting Current (LRA)
🛡️ Apply NEC 430 125% Rule
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FLA estimate (updates live)
Select motor details above

Calculating motor full load amps…

⚡ Motor FLA Results
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Full Load Amps (FLA)
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Single-phase · 115V
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A
FLA
🚀
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A
LRA (Start)
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A
MCA (NEC 125%)
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—
A
Breaker Size
🛡️ NEC Article 430 — Motor Protection Sizing
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Amps
Min Circuit Ampacity
FLA × 125% (NEC 430.22)
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Amps
Max Breaker (OCPD)
FLA × 250% max (NEC 430.52)
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Amps
Overload Relay Trip
FLA × 115–125% (NEC 430.32)
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AWG
Min Wire Gauge
Based on MCA at 75°C

📊 FLA at Different Voltages

Voltage
FLA
MCA
Breaker

📋 Full Calculation Summary

Parameter
Value
Note
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⚠️

Always Verify Against Motor Nameplate

This calculator estimates FLA using the standard electrical formula. The most accurate FLA is always the number printed on your motor’s nameplate. Local electrical codes may have additional requirements. Always have a licensed electrician verify the final circuit sizing.

🛠️ Application Notes

Motor FLA — What It Is and Why It Matters

FLA stands for Full Load Amps. It’s the most important number for sizing motor circuits. Here’s what it means and how to use it correctly.

⚡

What Is FLA?

FLA (Full Load Amps) is the amount of current a motor draws when running at full rated load. It’s the baseline number for all motor circuit calculations. Everything else — breaker size, wire gauge, overload protection — is calculated from FLA.

🔗

FLA vs. LRA vs. RLA

FLA is the running current at full load. LRA (Locked Rotor Amps) is the surge current when the motor first starts — typically 5–7 times the FLA. RLA (Rated Load Amps) is used specifically for compressors and accounts for the expected continuous running current.

📖

NEC Article 430

The National Electrical Code dedicates all of Article 430 to motors. It sets minimum circuit ampacity at 125% of FLA, maximum breaker sizes, and overload protection requirements. Following NEC 430 protects the motor and ensures your installation passes inspection.

📐

Why 125%?

Motors run continuously and generate heat in the wire over time. The 125% factor on FLA gives the circuit thermal headroom. Without it, a wire sized at exactly FLA would overheat during extended full-load operation. This is why NEC 430.22 requires MCA = FLA × 1.25.

🔌

Single Phase vs. Three Phase

A three-phase motor of the same horsepower draws about 58% of the amps of a single-phase motor, because power is shared across three conductors instead of one. This is why large motors always use three-phase — smaller wire, lower current, and more efficient power delivery.

🏷️

Nameplate is Always Right

Every motor has a data nameplate with the exact FLA for that specific unit. Our calculator gives accurate estimates, but the nameplate FLA is the authoritative value. Always use the nameplate number when sizing an actual installation.

📐 The Formulas We Use

FLA (Single Phase) = (HP × 746) ÷ (Volts × Efficiency × Power Factor) FLA (Three Phase) = (HP × 746) ÷ (Volts × 1.732 × Efficiency × Power Factor) MCA = FLA × 1.25  (NEC 430.22) Max OCPD = FLA × 2.50, rounded up to standard breaker (NEC 430.52)

746 watts = 1 HP (conversion constant). √3 ≈ 1.732 for three-phase power. Efficiency and power factor from the motor nameplate or typical values by motor class.

Motor FLA Reference Chart

NEC Table 430.248 values for single-phase motors.

Motor HP115V FLA230V FLAMCA (230V)Max Breaker (230V)
1/6 HP4.4A2.2A2.8A15A
1/4 HP5.8A2.9A3.6A15A
1/3 HP7.2A3.6A4.5A15A
1/2 HP9.8A4.9A6.1A15A
3/4 HP13.8A6.9A8.6A15A
1 HP16A8.0A10.0A20A
2 HP24A12A15.0A30A
3 HP34A17A21.3A45A
5 HP56A28A35.0A70A

Frequently Asked Questions

FLA stands for Full Load Amps. It’s the current your motor draws when running at its full rated horsepower. You’ll find it printed on the motor’s nameplate — the metal data plate attached to the motor housing. Look for “FLA”, “F.L.A.”, or “Amps” followed by a number. If the nameplate is damaged, use the NEC table values or this calculator as a close estimate.
FLA is the actual running current of the motor. MCA (Minimum Circuit Ampacity) is the minimum wire size and conductor rating required by the NEC — it equals FLA × 1.25. This 25% safety margin accounts for continuous duty heat buildup in the wire. You size the wire to the MCA, not directly to FLA. The breaker is sized separately and is usually larger than both.
No. Breakers for motors are sized much larger than FLA to handle the high inrush current during startup (LRA), which can be 5–7 times the FLA. NEC 430.52 allows breakers up to 250% of FLA for inverse-time breakers. A breaker sized at just FLA would trip every time the motor starts. Use the OCPD (Max Breaker) value this calculator provides.
The service factor (SF) tells you how much over the rated horsepower a motor can operate continuously without overheating. A motor with SF 1.15 can handle 115% of its rated load. When sizing overload protection, the NEC allows you to set it to FLA × SF × 1.15 for motors with a service factor ≥ 1.15 and ≥ 40°C rating. This tool accounts for service factor in the overload relay sizing calculation.
The same horsepower requires the same total wattage. In three-phase power, that wattage is spread across three conductors equally, so each conductor carries less current. The formula includes the √3 (1.732) factor to account for this distribution. For example, a 5 HP motor at 460V three-phase draws about 7.6A, while the same HP at 230V single-phase draws about 28A. This is why larger motors almost always use three-phase.
Per NEC 430.24, when multiple motors share a circuit: take the largest motor’s FLA × 1.25, then add the full FLA of every other motor at 100%. The result is the minimum circuit ampacity for the combined load. Use the Multi-Motor tab in this calculator to do this automatically for up to several motors on a single panel or feeder.
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