NEC Article 430 — Motors: What Every Electrician Needs to Know

Motor circuit problems are on virtually every electrician exam — and they're notorious for tripping up candidates who try to apply the same rules they use for lighting and receptacle circuits. Motors play by different rules, and Article 430 is complex enough that questions on it often separate passing candidates from those who fall short.

The key insight: motor circuits have four separate protection requirements, each sized differently. Once you understand what each one protects and how it's sized, Article 430 becomes manageable.

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The Four Motor Circuit Components

Every motor circuit has four elements that the NEC treats separately:

1. Branch circuit conductors — sized at 125% of FLC (430.22)
2. Short-circuit and ground-fault protection — sized larger than the conductors (430.52)
3. Overload protection — sized to protect the motor (430.32)
4. Disconnecting means — must be in sight and of adequate rating (430.102, 430.109)

Understanding why each is sized differently is as important as knowing the numbers.

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Full-Load Current (FLC) Tables: The Starting Point

Before sizing anything, you need the motor's full-load current. The NEC does not use the nameplate current for sizing branch circuit conductors and short-circuit protection — it uses the Table values.

NEC 430.6 states that for the purpose of sizing conductors and protection devices, the FLC values from the following tables shall be used (not the nameplate ampere rating):

• Table 430.247 — DC motors
• Table 430.248 — Single-phase AC motors
• Table 430.249 — Two-phase (induction) motors
• Table 430.250 — Three-phase AC motors

Exam tip: This is one of the most commonly missed Article 430 rules. You use the NEC table current, not the nameplate current, for sizing conductors and branch-circuit protection. The nameplate current is used for overload protection sizing.

Commonly Tested Table 430.248 Values (Single-Phase, 230V)

Commonly Tested Table 430.250 Values (Three-Phase, 230V/460V)

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Step 1: Branch Circuit Conductors — 430.22

NEC 430.22: Branch circuit conductors serving a single motor must have an ampacity of not less than 125% of the motor full-load current from the applicable Table.

Formula: Conductor ampacity ≥ FLC × 1.25

Example: 5 HP, 230V, single-phase motor:

• FLC from Table 430.248 = 28A
• Required conductor ampacity = 28 × 1.25 = 35A
• From Table 310.16 (75°C copper): 8 AWG = 50A ✓ (10 AWG = 35A, exactly meets minimum)

Several Motors on One Feeder: 430.24

Where a feeder supplies two or more motors, the conductor must be sized at 125% of the largest motor's FLC plus the FLC of all other motors.

Formula: Feeder ampacity ≥ (1.25 × Largest Motor FLC) + (Sum of all other motor FLCs)

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Step 2: Short-Circuit and Ground-Fault Protection — 430.52

This is where motor circuits diverge most dramatically from standard branch circuit rules.

NEC 430.52 permits the short-circuit and ground-fault protection device to be rated significantly larger than the conductor ampacity — because the motor needs a brief high-current surge to start.

Table 430.52 — Maximum Rating or Setting of Motor Branch-Circuit Short-Circuit and Ground-Fault Protective Devices:

Example: 10 HP, 230V, single-phase motor (FLC = 50A), inverse-time breaker:

• Maximum breaker size = 50A × 250% = 125A
• But a 125A standard breaker doesn't exist — use the next standard size down: 110A (or 100A, the next standard size)

Wait — the NEC also says if the calculated value doesn't correspond to a standard device size, you can go to the next higher standard size.

So 125A would round up to the next standard size: 125A (which is a standard size — check NEC 240.6(A)).

Exam tip: The most tested motor protection device is the inverse-time circuit breaker at 250%. Memorize this one.

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Step 3: Overload Protection — 430.32

Overload protection protects the motor against prolonged overload currents that cause overheating — it is completely separate from the branch circuit overcurrent protection.

NEC 430.32(A)(1) — Continuous-Duty Motors Over 1 HP:

Overload protection must not exceed:

• 115% of nameplate FLA for motors with a service factor (SF) of 1.15 or more, OR temperature rise of 40°C or less
• 125% of nameplate FLA for all other motors

Example: Motor nameplate shows FLA = 24A, SF = 1.15:

• Maximum overload setting = 24 × 1.15 = 27.6A

What If the Motor Won't Start?

If the calculated overload protection value is too small and the motor trips on starting:

• NEC 430.32(C) permits increasing overload protection up to 140% (for motors with SF ≥ 1.15 or 40°C temperature rise) or 170% for all others.

This is the "next size up" escalation for overloads that are tripping on legitimate motor starting.

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Step 4: Disconnecting Means — 430.102, 430.109

Location: 430.102

A disconnecting means must be provided in sight of and within 50 feet of the motor and the driven machinery, AND within sight of the motor controller.

"Within sight" means visible AND within 50 feet.

Exception: If the disconnect can be locked in the open position, it does not need to be in sight of the motor — but the lock must remain in place during servicing.

Type of Disconnect: 430.109

Permitted disconnecting means include:

• Motor-circuit switch rated in HP (most common for motors)
• Molded case circuit breaker
• Molded case switch
• Instantaneous-trip circuit breaker (with conditions)
• Self-protected combination controller (with conditions)

HP Rating: 430.110

The disconnecting means must be rated for at least 115% of the motor full-load current in amperes, and the HP rating must be at least equal to the motor HP.

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Motor Controller Requirements: 430.83

Every motor must have a controller. The controller must have a HP rating not lower than the motor HP (with some exceptions for small motors).

Controllers include starters, contactors, and manual switches — but not disconnecting means alone.

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Summary: The Four Numbers for Every Motor Circuit

For a 10 HP, 230V, single-phase motor (FLC = 50A from Table 430.248):

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Common Exam Mistakes on Article 430

1. Using nameplate current instead of table FLC for conductor and SCGF sizing
2. Applying 125% to the breaker — that's for conductors, not the breaker (the breaker can be up to 250%)
3. Confusing overload protection with short-circuit protection — they're separate devices sized differently
4. Forgetting the disconnect must be within 50 feet and within sight unless lockable
5. Missing the feeder formula (1.25 × largest + sum of others) when multiple motors are on one feeder

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Ready to Practice Article 430 Problems?

GetLicenseReady's practice questions include motor circuit calculations covering conductor sizing, protection device selection, overload protection, and disconnecting means requirements.

Related reading: NEC Table 310.16 — Wire Sizing and Ampacity | NEC Article 220 — Load Calculations | How to Pass the Electrician Exam on Your First Try