Motor Current Guide: FLC Tables & NEC 430 Requirements
Motor Nameplate vs FLC
Two current values matter for motors:
- Nameplate current: Actual current at rated load. Use for overload protection.
- Full Load Current (FLC): NEC table value for the motor's HP and voltage. Use for wire sizing and breaker selection. Always ≥ nameplate.
Why the difference? NEC tables use worst-case values for each HP rating. Your specific motor may be more efficient and draw less current. Always use NEC FLC tables for sizing — they provide a safety margin.
NEC Table 430.248 — Single-Phase FLC
| HP | 115V | 200V | 230V |
|---|---|---|---|
| 1/6 | 4.4 | 2.5 | 2.2 |
| 1/4 | 5.8 | 3.3 | 2.9 |
| 1/3 | 7.2 | 4.1 | 3.6 |
| 1/2 | 9.8 | 5.6 | 4.9 |
| 3/4 | 13.8 | 7.9 | 6.9 |
| 1 | 16 | 9.2 | 8.0 |
| 1-1/2 | 20 | 11.5 | 10 |
| 2 | 24 | 13.8 | 12 |
| 3 | 34 | 19.6 | 17 |
| 5 | 56 | 32.2 | 28 |
| 7-1/2 | 80 | 46 | 40 |
| 10 | 100 | 57.5 | 50 |
NEC Table 430.250 — Three-Phase FLC
| HP | 200V | 230V | 460V | 575V |
|---|---|---|---|---|
| 1/2 | 2.5 | 2.2 | 1.1 | 0.9 |
| 1 | 4.2 | 3.6 | 1.8 | 1.4 |
| 2 | 7.8 | 6.8 | 3.4 | 2.7 |
| 3 | 11 | 9.6 | 4.8 | 3.8 |
| 5 | 17.5 | 15.2 | 7.6 | 6.1 |
| 7-1/2 | 25.3 | 22 | 11 | 9 |
| 10 | 32.2 | 28 | 14 | 11 |
| 15 | 48.3 | 42 | 21 | 17 |
| 20 | 62.1 | 54 | 27 | 22 |
| 25 | 78.2 | 68 | 34 | 27 |
| 30 | 92 | 80 | 40 | 32 |
| 40 | 120 | 104 | 52 | 41 |
| 50 | 150 | 130 | 65 | 52 |
NEC 430 Motor Circuit Sizing Rules
| Component | Sizing Rule | NEC Reference |
|---|---|---|
| Wire (conductor) | 125% of motor FLC | 430.22 |
| Overload protection | 115% of nameplate current (service factor 1.15: 125%) | 430.32 |
| Branch circuit breaker (inverse-time) | 150% of FLC (250% for NEMA Design B motors) | 430.52 |
| Branch circuit fuse (non-time-delay) | 300% of FLC | 430.52 |
| Disconnect | 115% of motor FLC | 430.110 |
| Ground wire | Per NEC Table 250.122 | 250.122 |
Worked Example
Motor: 10 HP, 230V, 3-phase, Design B.
FLC (Table 430.250): 28A
Wire: 28 × 1.25 = 35A → 8 AWG copper (50A at 75°C, but 40A at 60°C)
Breaker: 28 × 2.50 = 70A → 70A inverse-time breaker
Overload: 28 × 1.25 = 35A → set thermal overload relay to 35A
Disconnect: 28 × 1.15 = 32.2A → 40A disconnect
Ground wire: Table 250.122 for 70A breaker → 10 AWG copper
Common Motor Current Mistakes
- Using nameplate instead of FLC: Wire and breaker must use NEC FLC (Table 430.248/250), not nameplate. Nameplate is only for overload protection.
- Using standard breaker rules: Motor breakers use NEC 430.52 (150–250% of FLC), NOT NEC 240.4(D) standard wire/breaker matching.
- Ignoring voltage drop on motor circuits: Motors are sensitive to voltage drop. Keep under 3% — low voltage causes high current and overheating.
Standards Reference
- NEC Article 430 — Motors
- NEC Table 430.248 — Single-Phase Motor FLC
- NEC Table 430.250 — Three-Phase Motor FLC
- NEMA MG-1 — Motors and Generators
Frequently Asked Questions
How do I find motor full load current?
Use NEC Table 430.248 (single-phase) or 430.250 (three-phase) based on the motor's HP and voltage. Always use the table value, not the nameplate, for wire sizing and breaker selection. Nameplate current is for overload protection only.
What size wire for a 5 HP motor at 230V 3-phase?
NEC Table 430.250: FLC = 15.2A. Wire = 15.2 × 1.25 = 19A (NEC 430.22). Use 12 AWG copper (25A at 75°C). Breaker = 15.2 × 1.5 = 22.8A → 25A inverse-time breaker (NEC 430.52).
Why is motor breaker larger than wire ampacity?
Motor breakers (NEC 430.52) allow 150–250% of FLC to handle starting inrush current (6–8× FLC for 1–2 seconds). The overload relay protects the wire from sustained overcurrent. This is a specific exception to the standard NEC 240.4 wire-breaker matching rules.
Can I use a standard breaker for a motor?
Not recommended. Standard breakers (NEC 240.4) would trip on motor starting current. Motor circuit breakers (inverse-time) have a delay characteristic that allows the brief starting surge. Use motor-rated circuit breakers or time-delay fuses per NEC 430.52.
What happens if motor voltage is too low?
Low voltage causes the motor to draw higher current to maintain torque, leading to overheating and premature failure. At 10% below rated voltage, current increases ~10% and temperature rises ~15%. Keep voltage drop under 3% for motor circuits.