Motor Full-Load Amps (FLA) Calculator

Find a motor’s full-load current straight from NEC Tables 430.248 and 430.250, pick horsepower, voltage, and phase and get the FLC that sizes your conductors and overcurrent protection, plus the 125% conductor ampacity and breaker/fuse maximums. Free, no signup.

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Motor FLA Calculator

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These only affect the theoretical calculated current below. The NEC table value still governs all sizing.

NEC full-load current (FLC)14 A

NEC Table 430.250 · 10 HP at 460 V

Min conductor ampacity
17.5 A125% of FLC, NEC 430.22
Max inverse-time breaker
35 A250% of FLC (35 A), next size up, NEC 430.52
Max dual-element fuse
25 A175% of FLC (24.5 A), next size up
Calculated current
12.2 A(HP × 746) ÷ (√3 × V × eff × PF), informational, table governs

Per NEC 430.6(A)(1), conductor and overcurrent sizing use the full-load current from Tables 430.248 (single-phase) and 430.250 (three-phase), not the nameplate or calculated value. Branch-circuit conductors must carry at least 125% of that FLC (430.22). Branch short-circuit / ground-fault protection may go up to 250% for an inverse-time breaker or 175% for a dual-element fuse, rounded up to the next standard rating (430.52).

The calculated current shown is the theoretical draw at your efficiency and power factor, useful for a sanity check, but it is normally lower than the conservative table value that the Code requires for sizing.

  • Choose phase, HP, and voltage

    Pick single- or three-phase, the motor horsepower, and the system voltage. The tool reads the full-load current directly from NEC Table 430.248 or 430.250.

  • Get the code sizing values

    See the minimum branch-circuit conductor ampacity (125% of FLC per 430.22) and the maximum inverse-time breaker and dual-element fuse (per 430.52), rounded to the next standard size.

  • Compare to the calculated current

    Enter efficiency and power factor to see the theoretical calculated current, a handy sanity check that is normally lower than the table value the Code requires for sizing.

How it works

  1. 1

    Choose phase, HP, and voltage

    Pick single- or three-phase, the motor horsepower, and the system voltage. The tool reads the full-load current directly from NEC Table 430.248 or 430.250.

  2. 2

    Get the code sizing values

    See the minimum branch-circuit conductor ampacity (125% of FLC per 430.22) and the maximum inverse-time breaker and dual-element fuse (per 430.52), rounded to the next standard size.

  3. 3

    Compare to the calculated current

    Enter efficiency and power factor to see the theoretical calculated current, a handy sanity check that is normally lower than the table value the Code requires for sizing.

Why the NEC table value, not the nameplate

A motor’s full-load current drives everything downstream: conductor size, disconnect rating, and overcurrent protection. NEC 430.6(A)(1) is explicit that these are sized from the full-load current values in Tables 430.247 through 430.250, not the motor nameplate and not a calculated figure. Modern high-efficiency motors often have a lower nameplate FLA than the table, but the Code still uses the conservative, standardized table value so an installation works with any replacement motor of the same rating. The nameplate FLA is used only for overload (running) protection under 430.32.

This calculator reads the full-load current directly from NEC Table 430.248 for single-phase motors (115-230 V) and Table 430.250 for three-phase induction motors (200-575 V). From that value it derives the branch-circuit conductor minimum (125% of FLC, NEC 430.22) and the maximum short-circuit and ground-fault protection, 250% for an inverse-time breaker and 175% for a dual-element time-delay fuse, rounded up to the next standard rating per 430.52. It also shows the theoretical calculated current, I = (HP × 746) ÷ (√3 × V × efficiency × power factor) for three-phase, so you can see how it compares to the table. Pair it with the wire size calculator to turn the required ampacity into a conductor gauge.

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Motor FLA Calculator FAQs

Full-load amps, called full-load current (FLC) in the Code, is the current a motor draws at its rated horsepower and voltage. For NEC sizing you use the value from Table 430.248 (single-phase) or 430.250 (three-phase). For example, a 10 HP, 460 V three-phase motor is 14 amps, and a 5 HP, 230 V single-phase motor is 28 amps.
Use the NEC table value for sizing conductors, disconnects, and branch-circuit protection, NEC 430.6(A)(1) requires it. The nameplate FLA is used only for sizing the motor’s overload protection (430.32). High-efficiency motors often have a lower nameplate value, but you must still size the circuit to the table.
Branch-circuit conductors for a single continuous-duty motor must have an ampacity of at least 125% of the full-load current from the NEC table (NEC 430.22). A 10 HP, 460 V motor at 14 A needs conductors rated at least 17.5 A; a 40 HP motor at 52 A needs at least 65 A.
Branch-circuit short-circuit and ground-fault protection can be sized up to 250% of the full-load current for an inverse-time breaker or 175% for a dual-element time-delay fuse, then rounded up to the next standard size (NEC 430.52). A 50 HP, 460 V motor at 65 A allows up to a 175 A breaker or a 125 A dual-element fuse.
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