Motor Full-Load Current (FLC) Calculator
NEC Article 430 Part XIV full-load current lookup by horsepower and voltage: Table 430.248 (single-phase), 430.249 (two-phase) and 430.250 (three-phase, including synchronous motors at unity, 90% and 80% power factor), with the 125% branch-circuit conductor sizing rule applied.
How this is calculated
NEC 430.6(A)(1) requires motor branch-circuit and feeder conductor sizing, overload protection, and short-circuit protection to be based on the table full-load current value for the motor's horsepower and voltage — not the motor's actual nameplate current, even if they differ. Tables 430.248, 430.249 and 430.250 give those standardized values for single-phase, two-phase and three-phase motors.
Min. conductor ampacity = FLC × 1.25 (NEC 430.22, single continuous-duty motor)
This 125% factor covers the single most common case: one continuous-duty motor on its own branch circuit. Multi-motor circuits, intermittent-duty motors, and overload/short-circuit protection device sizing (NEC 430.32, 430.52) follow different, motor-type-dependent rules not covered by this calculator.
Table 430.250 — Three-Phase (reference)
| HP | 115V | 200V | 208V | 230V | 460V | 575V | 2300V |
|---|---|---|---|---|---|---|---|
| 1/2 | 4.4 | 2.5 | 2.4 | 2.2 | 1.1 | 0.9 | — |
| 3/4 | 6.4 | 3.7 | 3.5 | 3.2 | 1.6 | 1.3 | — |
| 1 | 8.4 | 4.8 | 4.6 | 4.2 | 2.1 | 1.7 | — |
| 1-1/2 | 12 | 6.9 | 6.6 | 6 | 3 | 2.4 | — |
| 2 | 13.6 | 7.8 | 7.5 | 6.8 | 3.4 | 2.7 | — |
| 3 | — | 11 | 10.6 | 9.6 | 4.8 | 3.9 | — |
| 5 | — | 17.5 | 16.7 | 15.2 | 7.6 | 6.1 | — |
| 7-1/2 | — | 25.3 | 24.2 | 22 | 11 | 9 | — |
| 10 | — | 32.2 | 30.8 | 28 | 14 | 11 | — |
| 15 | — | 48.3 | 46.2 | 42 | 21 | 17 | — |
| 20 | — | 62.1 | 59.4 | 54 | 27 | 22 | — |
| 25 | — | 78.2 | 74.8 | 68 | 34 | 27 | — |
| 30 | — | 92 | 88 | 80 | 40 | 32 | — |
| 40 | — | 120 | 114 | 104 | 52 | 41 | — |
| 50 | — | 150 | 143 | 130 | 65 | 52 | — |
| 60 | — | 177 | 169 | 154 | 77 | 62 | 16 |
| 75 | — | 221 | 211 | 192 | 96 | 77 | 20 |
| 100 | — | 285 | 273 | 248 | 124 | 99 | 26 |
| 125 | — | 359 | 343 | 312 | 156 | 125 | 31 |
| 150 | — | 414 | 396 | 360 | 180 | 144 | 37 |
| 200 | — | 552 | 528 | 480 | 240 | 192 | 49 |
| 250 | — | — | — | — | 302 | 242 | 60 |
| 300 | — | — | — | — | 361 | 289 | 72 |
| 350 | — | — | — | — | 414 | 336 | 83 |
| 400 | — | — | — | — | 477 | 382 | 95 |
| 450 | — | — | — | — | 515 | 412 | 103 |
| 500 | — | — | — | — | 590 | 472 | 118 |
In-depth guide: Sizing a motor branch circuit under NEC Article 430
How this calculator works
NEC Table 430.248 (single-phase), Table 430.249 (two-phase, 4-wire) and Table 430.250 (three-phase, including the synchronous-type unity power factor columns and the 1.1 / 1.25 footnote multipliers for 90% / 80% power factor) full-load current; 125% conductor sizing per NEC 430.22. European mode: I = P / (√3 × U × η × cos φ) with the IE3 minimum efficiencies of Commission Regulation (EU) 2019/1781, Annex I.
Worked example
A 10 hp three-phase motor at 460 V.
Table 430.250 gives a full-load current of 14 A. Branch-circuit conductors for a single continuous-duty motor must be at least 125% of that: 14 × 1.25 = 17.5 A minimum conductor ampacity.
The same 10 hp motor at 208 V draws 30.8 A from the table — about 2.2 times the current at 460 V, which is why larger motors are usually run at the higher voltage.
Frequently asked questions
Should I use the nameplate current or the table value?
For conductor sizing, short-circuit and ground-fault protection, NEC 430.6(A)(1) requires the table full-load current, not the nameplate. The nameplate current is used for sizing overload protection.
Why 125%?
NEC 430.22 requires branch-circuit conductors for a single continuous-duty motor to have an ampacity of at least 125% of the motor's full-load current, to cover starting and running heat.
What about 230 V motors on a 208 V system?
Use the column for the actual system voltage. A motor nameplated 208-230 V running on 208 V draws more current, so the 208 V column (or 200 V for some tables) gives the right value.
Does this size the breaker too?
No. Branch-circuit short-circuit and ground-fault protection follows NEC 430.52 and depends on the device type and motor design — it is often well above 125%.
What is the full-load current of a 25 hp, 575 V synchronous motor at unity power factor?
Using Part XIV of Article 430, Table 430.250 lists synchronous-type motors at unity power factor in separate columns: a 25 hp, 575 V synchronous motor has a full-load current of 21 A (26 A at 460 V, 53 A at 230 V). Its branch-circuit conductors need at least 21 × 1.25 = 26.25 A.
How do I find the full-load current of a synchronous motor at 90% or 80% power factor?
Take the unity-power-factor value from Table 430.250 and multiply it by 1.1 for 90% or 1.25 for 80%, as the table footnote requires. A 75 hp, 230 V synchronous motor is 155 A at unity, 170.5 A at 90% and 193.75 A at 80%.
Which table covers two-phase motors?
Table 430.249 (two-phase, 4-wire). A 7-1/2 hp, 460 V two-phase motor has a full-load current of 9.0 A. In a 2-phase, 3-wire system the common conductor carries 1.41 times the table value.
Common mistakes
- Sizing wire or breaker from the nameplate. NEC 430.6(A)(1) requires the table full-load current for conductors and short-circuit protection. The nameplate current is for overloads.
- Using the 230 V column on a 208 V system. Use the column for the actual system voltage. A 10 hp three-phase motor is 28 A in the 230 V column but 30.8 A in the 208 V column.
- Forgetting the synchronous power-factor multiplier. The synchronous columns of Table 430.250 are for unity power factor. Multiply by 1.1 at 90% and by 1.25 at 80% power factor.
- Sizing the breaker at 125%. The 125% rule is for conductors. Branch short-circuit protection follows Table 430.52 (up to 250% of FLC for an inverse-time breaker).
What it does not cover
Overload and short-circuit protection sizing, multi-motor circuits.
Sources
- NFPA 70, National Electrical Code (free read-only access)
- Commission Regulation (EU) 2019/1781, ecodesign requirements for electric motors (EUR-Lex)
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