NEC 430.248 & 430.250
Motor Full-Load Current (FLC, Wire & Breaker)
Enter horsepower, voltage and phase and get the circuit: full-load current, the conductor at 125% and the maximum inverse-time breaker at 250%. Use the table value, not the nameplate, to size the branch circuit.
Enter the motor's horsepower, not its nameplate amps. NEC 430.6(A)(1) sizes the branch circuit from the table full-load current; the nameplate current sizes only the running overload device (430.32).
NEC Table 430.25014 A
NEC 430.22, 125% of FLC17.5 A
75C column, NEC Table 310.16#14
NEC 430.52(C)(1) Exc. 1, 250% of FLC35 A
The 35A breaker is deliberately larger than the #14 conductor's ampacity so the motor can draw its starting current without tripping. That is code-correct: NEC 240.4(G) exempts motor branch-circuit conductors from the small-conductor limits of 240.4(D), and the running overload device (430.32), not the branch breaker, is what protects the conductor from overload.
This is the maximum standard breaker permitted for a single motor on this branch circuit. A smaller device is usually permitted and is often required by the actual starting characteristics. Long runs may need a larger conductor for voltage drop, which this calculation does not include. Your AHJ and local amendments govern the install.
What this sizes. Induction-type squirrel-cage and synchronous motors, which is the ordinary case and the row of NEC Table 430.52 this 250% comes from. A wound-rotor or DC motor takes a lower branch-circuit percentage from a different row of that table, so this result does not apply to one. Size those from Table 430.52 directly.
Check voltage drop on the run →Size a motor circuit by horsepower →Show the math
Step 1: the table full-load current10 HP, 460V, three-phase → 14 A (NEC Table 430.250)
Read from the table, never from the nameplate. NEC 430.6(A)(1) is explicit: the table current sizes the conductor, the branch-circuit device and the disconnect.
Step 2: the conductor14 A × 1.25 = 17.5 A (NEC 430.22)
Smallest copper conductor carrying 17.5 A in the 75°C column of Table 310.16: #14.
Step 3: the maximum branch-circuit device14 A × 2.50 = 35 A (Table 430.52, inverse-time breaker)
That is already a standard rating in NEC 240.6(A), so the maximum is 35 A.
The percentages above are the ones Table 430.52 gives an inverse-time breaker on a squirrel-cage motor. A wound-rotor or DC motor takes a different percentage, so this working does not carry across to them.
Where this number comes fromIntry Verified
- Calculated from
- NEC Table 430.250, NEC 430.6(A)(1), 430.22, 430.52(C)(1), Table 310.16, 240.6(A). Full-load current read from NEC 2023 Table 430.250 (three-phase) or Table 430.248 (single-phase) per 430.6(A)(1); conductor computed at 125 percent of that current against the 75C column of Table 310.16 per 430.22; maximum inverse-time breaker computed at 250 percent against the standard ratings in 240.6(A) per 430.52(C)(1) and its Exception 1. See the full receipt ↓
- Run with
- PhaseThree-phase
- Voltage460 V
- Horsepower10 HP
- Table FLC14 A
- Conductor materialCopper
- Terminals75°C
- Checked
- Every figure an Intry calculator computes comes from a locked source module, not hand-typed. 21026 automated checks re-derive and source-check the numbers against the cited NEC Table 430.250 and 430.248 full-load currents and the Article 430 branch-circuit rules before each deploy. This is our own deterministic gate, not a third-party audit.
- Final say
- Your AHJ has final say. The table current sizes the branch circuit; your motor's nameplate sizes the running overload device (430.32), which this tool does not size. Wound-rotor and DC motors take a different percentage from Table 430.52 and are out of scope.
Intry Verified · NEC 2023 · Build AE2FC52 · 2026-08-21
How to Size a Motor Branch Circuit
A motor circuit is sized differently from an ordinary load, and it turns on one rule that trips people up: you size the circuit from the NEC table full-load current, not the motor nameplate. NEC 430.6(A)(1) says the values in Tables 430.247 through 430.250 determine the conductor ampacity, the disconnect, and the branch-circuit short-circuit and ground-fault protective device. The nameplate full-load amps (FLA) is used only to size the running-overload device (430.6(A)(2) and 430.32).
From the table FLC, the branch circuit has two independent parts. The conductor is sized so its ampacity is at least 125% of the FLC (NEC 430.22). The short-circuit/ground-fault breaker may be sized up to 250% of the FLC for a standard inverse-time breaker (NEC 430.52 and Table 430.52), rounded up to the next standard size if needed to let the motor start (430.52(C)(1) Exception 1). That is why a motor circuit legally shows a small conductor under a large breaker: the conductor is protected from sustained overload by the separate overload device (430.32), and motor conductors are exempt from the 240.4(D) small-conductor limit via 240.4(G). The tables below apply these rules to the table FLC.
Motor Branch-Circuit Sizing (Conductor & Breaker)
| HP | FLC (A) | Min. conductor (75°C Cu) | Max. inverse-time breaker |
|---|---|---|---|
| 1/6 | 2.2 | #14 | 15A |
| 1/4 | 2.9 | #14 | 15A |
| 1/3 | 3.6 | #14 | 15A |
| 1/2 | 4.9 | #14 | 15A |
| 3/4 | 6.9 | #14 | 20A |
| 1 | 8 | #14 | 20A |
| 1-1/2 | 10 | #14 | 25A |
| 2 | 12 | #14 | 30A |
| 3 | 17 | #12 | 45A |
| 5 | 28 | #10 | 70A |
| 7-1/2 | 40 | #8 | 100A |
| 10 | 50 | #6 | 125A |
| HP | FLC (A) | Min. conductor (75°C Cu) | Max. inverse-time breaker |
|---|---|---|---|
| 1/2 | 1.1 | #14 | 15A |
| 3/4 | 1.6 | #14 | 15A |
| 1 | 2.1 | #14 | 15A |
| 1-1/2 | 3 | #14 | 15A |
| 2 | 3.4 | #14 | 15A |
| 3 | 4.8 | #14 | 15A |
| 5 | 7.6 | #14 | 20A |
| 7-1/2 | 11 | #14 | 30A |
| 10 | 14 | #14 | 35A |
| 15 | 21 | #10 | 60A |
| 20 | 27 | #10 | 70A |
| 25 | 34 | #8 | 90A |
| 30 | 40 | #8 | 100A |
| 40 | 52 | #6 | 150A |
| 50 | 65 | #4 | 175A |
| 60 | 77 | #3 | 200A |
| 75 | 96 | #1 | 250A |
| 100 | 124 | #2/0 | 350A |
| 125 | 156 | #3/0 | 400A |
| 150 | 180 | #4/0 | 450A |
| 200 | 240 | 350 kcmil | 600A |
Conductor is the smallest 75°C copper wire whose Table 310.16 ampacity meets 125% of the FLC (valid for THHN/THWN-2 on 75°C terminals); NM-B cable is limited to the 60°C column. The breaker shown is the maximum permitted short-circuit/ground-fault device; a smaller standard size is used when the motor will start on it. Overload protection is separate and sized from the nameplate (430.32).
Worked Example
10 HP, 460V, three-phase motor
Table 430.250 FLC = 14A. Conductor = 14 × 1.25 = 17.5A. Breaker = 14 × 2.5 = 35A.
The conductor needs 17.5A of ampacity, so #14 copper (20A at 75°C) works. The maximum inverse-time breaker is 35A, which is a standard size. So the branch circuit is #14 copper on a 35A breaker, with the overload device set from the nameplate (about 125% of nameplate FLA). If you had (wrongly) sized from a nameplate reading of, say, 13A, you would get a different, non-code result. The table value governs.
Frequently Asked Questions
What is the full-load current of a 1 HP motor?
Per NEC Table 430.248, a single-phase 1 HP motor is 16A at 115V and 8A at 230V. Per NEC Table 430.250, a three-phase 1 HP motor is 4.2A at 230V, 2.1A at 460V, and 1.7A at 575V. Use these table values, not the nameplate amps, to size the branch-circuit conductors and the short-circuit/ground-fault breaker (NEC 430.6(A)(1)).
Do I use the nameplate amps or the NEC table to size a motor circuit?
Use the NEC table. NEC 430.6(A)(1) requires the values in Tables 430.247 through 430.250 to size the branch-circuit conductors, the ampacity, the disconnect, and the short-circuit/ground-fault protective device. The motor nameplate full-load amps (FLA) is used only to size the running-overload device, per 430.6(A)(2) and 430.32. This is the single most common motor-circuit mistake.
What size wire and breaker for a 10 HP three-phase motor at 460V?
A 10 HP, 460V, three-phase motor has a table full-load current of 14A (NEC Table 430.250). The branch-circuit conductor is sized at 125% of FLC = 17.5A, which is #14 copper at the 75°C column. The maximum inverse-time breaker is 250% of FLC = 35A (NEC 430.52, Table 430.52). So #14 copper on a 35A breaker, with the overload device set from the nameplate. The small #14 conductor under a 35A breaker is code-correct because motor conductors are exempt from the 240.4(D) small-conductor rule (240.4(G)); the overload device protects the wire, not the breaker.
Why is the motor breaker so much bigger than the wire ampacity?
A motor draws several times its running current for a moment at startup (locked-rotor / inrush). NEC 430.52 lets the branch-circuit short-circuit/ground-fault breaker be sized up to 250% of the full-load current (inverse-time type) so it does not trip on that inrush. The conductor is only sized to 125% of FLC (430.22) and is protected against sustained overload by the separate overload device (430.32), not by the branch breaker. That is why you see a small conductor under a large breaker on a motor circuit, and why motor conductors are exempt from the 240.4(D) small-conductor limit via 240.4(G).
What is the full-load current of a 5 HP single-phase motor at 230V?
Per NEC Table 430.248, a 5 HP single-phase motor at 230V has a full-load current of 28A (56A at 115V). Sized to 125%, the conductor ampacity is 35A, which is #10 copper at 75°C, and the maximum inverse-time breaker is 70A per NEC 430.52.
Are the NEC motor FLC tables the same in the 2017, 2020, and 2023 editions?
Yes. The full-load current values in NEC Tables 430.248 (single-phase) and 430.250 (three-phase) have not changed across the 2017, 2020, and 2023 editions of NFPA 70. The section numbers for the sizing rules (430.6, 430.22, 430.32, 430.52) are also unchanged.
How do I size motor overload protection?
Overload protection is sized from the motor nameplate full-load amps (FLA), not the NEC table. Per NEC 430.32(A)(1), a continuous-duty motor over 1 HP uses 125% of nameplate FLA when the motor has a marked service factor of 1.15 or higher, or a marked temperature rise of 40°C or less; otherwise 115%. This overload device, separate from the branch-circuit breaker, is what protects the motor and conductor from a sustained overload.
Related Calculators & Charts
Three-Phase Motor Calculator
Know the motor? Enter horsepower and voltage and get that circuit: the conductor at 125% and the maximum inverse-time breaker at 250%, off these same tables.
Wire Ampacity Chart (310.16)
Check what a conductor already in place carries, once the motor conductor is sized, at 60, 75, and 90°C.
Wire Size for a Well Pump
The most common single-phase motor branch circuit, worked all the way through with the same rules.
Standard Breaker Sizes (240.6)
The standard OCPD ratings the motor breaker is rounded up to under 430.52 Exception 1.
Have the FLC. Now size the whole circuit.
The wire size calculator sizes any conductor for a load and picks the protecting breaker, and the well-pump and air-compressor pages walk a real motor branch circuit end to end.
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