Motor FLC Calculator
Look up motor full-load current from NEC Table 430.248/430.250, then get the 125% branch-circuit conductor ampacity, the 430.52 maximum protection by device type, and the disconnect rating. Free, no sign-up.
What to calculate next
Tools commonly used alongside this calculation
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Voltage Drop Calculator
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Conduit Fill Calculator
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Explanation
Sizing a motor circuit starts with the full-load current (FLC). Under NEC 430.6(A)(1), the FLC you use for the conductors and the branch-circuit protective device comes from Table 430.248 (single-phase) or Table 430.250 (three-phase) — not the motor nameplate. From that one number you get the minimum conductor ampacity, the maximum short-circuit and ground-fault protection, and the disconnect rating. This calculator looks up the FLC for the horsepower and voltage you choose and works out each of those values per NEC Article 430.
How motor circuit sizing works
Once the FLC is fixed by the table, three multipliers do most of the work. The branch-circuit conductor must carry at least 125% of the FLC (430.22), the disconnecting means must be rated for at least 115% (430.110), and the branch-circuit short-circuit and ground-fault device has a ceiling set by 430.52 that depends on the device type.
| Term | Meaning |
|---|---|
| FLC | Full-load current from NEC Table 430.248 / 430.250 |
| 430.22 | Branch-circuit conductor at 125% of FLC |
| 430.52 | Maximum short-circuit / ground-fault protective device |
| 430.110 | Disconnecting means at 115% of FLC |
The 125% conductor figure is a minimum ampacity, not a wire size — you still pick the gauge whose ampacity (after any ambient and conductor-count derating) meets it. Carry the result into the wire size & ampacity calculator to choose the conductor, and the conduit fill calculator when those conductors share a raceway.
Branch-circuit protection by device type (430.52)
NEC Table 430.52 caps the branch-circuit short-circuit and ground-fault protective device at a percentage of the FLC, and the percentage is far higher than for a normal load because the device only has to ride through the motor’s inrush, not protect against overload. Overload is handled separately by 430.32.
| Protective device | Max % of FLC |
|---|---|
| Non-time-delay fuse | 300% |
| Dual-element (time-delay) fuse | 175% |
| Instantaneous-trip breaker | 800% |
| Inverse-time breaker | 250% |
These are maximums. When the calculated value does not match a standard breaker or fuse size, 430.52(C)(1) Exception 1 permits rounding up to the next standard size. The values apply to the common AC squirrel-cage and synchronous motors; Design B energy-efficient motors and certain other types use higher percentages noted under Table 430.52.
Full-load current tables (430.248 / 430.250)
The full-load currents below are the same across the 2017, 2020, and 2023 NEC editions. The calculator includes every voltage column — 115 through 2300 V — while the tables here show the most common ratings.
Notes and limitations
Use the table FLC for conductors and protection, but use the motor nameplate FLA for the overload device under 430.32 — typically 125% of the nameplate amps for a motor with a service factor of 1.15 or higher or a temperature rise of 40 °C or less, and 115% otherwise. Enter the nameplate FLA above to see that overload figure.
This tool sizes a single continuous-duty motor branch circuit. It does not size a feeder for several motors (430.24/430.62), apply the special percentages for Design B energy-efficient motors, or check that the protective device actually lets the motor start — bump up within the 430.52 ceiling if it trips on inrush. On long runs also check the voltage drop on the branch circuit. Always confirm the final design against the current NEC and the authority having jurisdiction.