Motor FLA Calculator

About the Motor FLA Calculator

This Motor Full Load Amps (FLA) Calculator looks up NEC Table 430.248 (single-phase) and Table 430.250 (three-phase) values for standard motor HP and voltage combinations. Use these conservative values for sizing motor branch circuits, breakers, and overload protection per NEC 430 requirements — this is the code-required reference for motor circuit design.

NEC FLA values are intentionally higher than typical nameplate FLA to provide safety margin across all motor designs. For code compliance, always use the larger of the table FLA or nameplate FLA when sizing.

How NEC FLA tables work

Branch circuit ampacity = NEC FLA × 1.25 (NEC 430.22)

NEC tables list FLA by HP and voltage. Multiply by 1.25 to get the minimum continuous-load conductor and breaker ampacity. Use the larger of the calculated value or the connected motor’s actual nameplate FLA for code-compliant sizing.

Worked example

A 25 HP, 460V three-phase motor: NEC Table 430.250 FLA = 34 A. Branch circuit minimum: 34 × 1.25 = 42.5 A. Specify a 45 A breaker and #8 AWG copper THHN (50 A ampacity at 75°C). Overload relay set at nameplate FLA × 1.15 (typical).

When to use this calculator

• Sizing motor branch circuits to code (NEC 430.22)
• Selecting motor circuit breakers and disconnects
• Specifying overload relay heater elements
• Designing motor control centers (MCCs)
• Verifying existing installations meet current code
• Preparing electrical drawings for permits

Code-compliant motor circuit sizing

Per NEC 430, a motor branch circuit must include:

• Conductors: ampacity ≥ FLA × 1.25
• Disconnect: ampacity ≥ FLA × 1.15
• Branch circuit overcurrent (breaker/fuse): typically FLA × 2.5 to 4.0 depending on type (allows for starting current)
• Overload relay (running protection): nameplate FLA × 1.15–1.25 depending on service factor

The breaker is sized for STARTING current (which is 6–10× FLA momentarily). The overload relay protects against RUNNING overcurrent.

Frequently Asked Questions

What is FLA?

Full Load Amps — the current a motor draws while delivering its nameplate horsepower. NEC tables list standardized FLA values by HP and voltage, conservatively higher than typical motor nameplate values to provide design margin.

Should I use NEC table FLA or motor nameplate FLA?

For sizing branch circuits, use the LARGER of table FLA or nameplate FLA. For sizing overload relays (running protection), use nameplate FLA. NEC 430.6 requires the table value for circuit sizing because it accounts for variation across motor manufacturers.

Why is the NEC table value higher than my motor nameplate?

NEC tables are conservative across all motor designs. Modern Premium-efficiency motors typically draw 5–15% less than the table value. The conservative approach ensures circuit safety even if a future replacement motor draws more current.

What is the 1.25 multiplier in NEC 430.22?

It accounts for “continuous load” operation — defined by NEC as 3+ hours of continuous current. The 25% margin keeps conductors and breakers from operating at their thermal limits. It applies only to branch circuit conductor and breaker sizing, not overload relays.

How do I size a breaker for motor starting?

Per NEC 430.52, an inverse-time circuit breaker can be sized at 250% of FLA (or 400% for Design B energy-efficient motors). Example: 34 A FLA × 250% = 85 A — round up to a standard 100 A breaker. The overload relay handles continuous protection.

Do I need to derate FLA for elevation or ambient temperature?

NEC FLA values assume standard conditions. For motors operating above 1,000 m elevation or in ambient > 40°C, derate the motor’s continuous capacity per nameplate or NEC 430.32(C). Branch circuit sizing typically isn’t affected.

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