NEC Article 430 — Motors, Motor Circuits, and Controllers
Article 430 governs the installation and protection of motors, motor branch circuits, motor feeders, motor controllers, and disconnecting means. This page covers the most common field questions: conductor sizing, overload protection, and short-circuit / ground-fault protection (SCPD) sizing.
Use Table FLC, Not Nameplate FLA
For conductor and SCPD sizing, NEC 430.6(A) requires using the full-load current values from Tables 430.248, 430.249, or 430.250 — not the actual nameplate FLA. Use nameplate FLA only when sizing overload protection (Section 430.32).
Branch-Circuit Conductor Sizing
| Application | Rule |
|---|---|
| Single motor, continuous duty | 125% of full-load current (FLC) — NEC 430.22(A) |
| Motor used in short-time, intermittent, or varying duty | Percentage of FLC per Table 430.22(E) depending on duty cycle |
| Several motors on same circuit | 125% of largest motor FLC + 100% of remaining motors — NEC 430.24 |
| Motor feeder conductors | 125% of largest motor + sum of other motor FLCs — NEC 430.24 |
Overload Protection (430.32)
| Device / Motor Type | Rule |
|---|---|
| Separate overload device (Class 10–20) | ≤ 125% of motor FLA for motors with marked service factor ≥ 1.15 or temp rise ≤ 40°C; ≤ 115% otherwise — NEC 430.32(A)(1) |
| Integral thermal protector | Listed and marked as provided; manufacturer rating applies |
| SCPD when no separate overload | Allowable for hermetically sealed motors with specific marking — see 430.32(A)(2) |
SCPD Sizing — Maximum Percentages (Table 430.52)
Maximum rating of the short-circuit and ground-fault protection device (SCPD) as a percentage of motor FLC (from Tables 430.248–430.250). These are maximums — you can always go smaller.
| Motor Type | Inverse Time Breaker | Dual-Element Fuse |
|---|---|---|
| Single-phase, all types | 250% | 175% |
| AC polyphase (squirrel cage, other than Design B) | 250% | 175% |
| Design B energy-efficient (> 30 HP) | 250% | 175% |
| Wound rotor | 150% | 150% |
| Direct current | 150% | 150% |
| Reluctance synchronous (high reactance) | 200% | 150% |
Disconnecting Means (430.102)
- • Required for each motor and controller.
- • Must be within sight of the motor location and within sight of the controller — or the controller shall be capable of being locked in the open position.
- • Must be rated in horsepower or amperes equal to or greater than the motor.
- • Must open all ungrounded supply conductors.
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